IIIHH H “HI I I 1 HIM! l ‘l fr‘ gtfa: u paw-:15 fizzy; , «'1' g; aragngp' 2".” Why: £33. Csm\( .iaa‘ M‘D gaff 12% h. ramp} ‘ 5,: 1r- . 333's! y” ego-Mgr; . 3-1; V? 3‘ 5‘ wake‘iv Nahum 5.34%: g&gW!1{O"?L‘KE $44!": ‘ W 22.8" LfiRE SHGRT-TQME RASTLLEZER T3355: 5m $325 Regrets cf M. S. “i-fififisbé STziTE COLLEGE wsefiaxa jam «2-, i1: Mlfifihfi We; 3 , ‘ Izmmmm:mumnwmunmmmm1 3 1293 00850 3645 ‘ I .5,— - ‘1 This is to certify that the ---c— - thesis cit-titled - Design, Operation and Efficiency 01 . 8 Producer Size Electro-pure Pasteurlzer. presented by Mr. Theodore J. liucha has been accepted towards fulfillment of the requirements for Mdegree in Dairy /”' Major professor Date May 264 19h8 A-.. _~'¢-—?—.-._ -- H-O—‘O ‘, fl-~—.-__—r -.-v._~. i.- U r - —~ “a Wk.- .fi. _ -V PLACE IN RETURN BOX to remove this checkout from your mood. TO AVOID FINES return on or beta. dds duo. [,1 DATE DUE DATE-DUE DATE DUE MSU Is An Affirmative Action/Equal Opportunity Institution cAdemS-pd MW, OPERATION AND UTICIRICY OF A PROHJGER SIZE W- PURE mammmm SEEP-Tm 2mm DEIGN, OPERATION AND HHCIINCY OF A PROWCm SIZE RECTRO" PURE EIGH'TDIPMTURE 3mm PASTEJPIZEI by Theodore Joseph Much: nun-u. ATEESIS Submitted to the Graduate School of mongol! State College of Agriculture and Applied Science in partial fulfilment of the ruminants tor the degree of IASI‘ER or same: Dairy Depamont 194B ’ TABLE OF CONTENTS mmmon COOOOIOOOOOOOOOOOOO0......COO...0..OOOOOOOOOOOOOOOOOOOOOOOO a. soap. or Investigation 00.000.00.00.000000000000000000000 REVIEW or ”W .......... ...... .eeeoooeeeeeeeeeeecon-000%~r-eeeooo 1. 2. .3. 4. 5. 6. 'I. 8. 9. 10. 11. 12. 13. 14. Early develoyment of electric pacteurizerc .................... Present types of high-taperature short-time pasteurizers ..... Checking equipment ............................................ Cleaning of equipment ......................................... Sterilization of equipment .................................... Effect on acidity ............................................. Effect on cream line .......................................... Effect on flavor .............................................. Effect on chemical composition ................................ Effect cn.phcsphatase .....................................,... Effect on total bacterial content ............................. Effect on thermcdnricc ........................................ Bfect on themephilce ........................................ meat on califom omamma .0...OOOOOOOOOOOOOOOOOO0.00.0.0... mm mom CCOOOOOOOOOOO0.0000000000000000000000'.0.0.00.0... LPWMON W1. OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOC 1. \ Description ................., .. ............................. near. 1 0...0...0.0.0.0000...000.000.0000.00000000000000... ‘0 Sure. tank OOOOOOOOOOOO0.0000000000000000000.0.0.00.0... be Piping eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee c. Valves ................................................. d. Pups 0.0.0.000...OOOOOOOOOOOOOOOO0.00000000000000000000 .0 Mtator 0......00.00.0000...OOOOOIOOOOOOOOOOOO00.0.0... :0 meter section OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO. 8. memmetors OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO h. &1°n°1d my. 00.000.000.000...OOOOOOOIOOOOOOOOOOOOOOOO 2033151 Page 10 13 15 16 1 7 18 Page i. Diversion.valve ..................................... 35 1. Cooling section ..................................... 35 k. mtches 0.0...OOOOOOOOOOOOOOOOOOOOOOOO0..0.0.0.0.... 35 1e Electrical contmls eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee 35 (1) Paddles OOOOOOOOOO0.0.0.00.00.00.00.00.0.0.0... 35 (2)8].1d1n8b01 OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO 36 (3) Resistance stabilizer ......................... 36 n, Holding section ..................................... 36 2. Checking equiment eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee 36 a. Revolutions per'minute .............................. 36 b. Checking accuracy of thermometers ................... 37 Ce 33151113 time deteminations eeeeeeeeeeeeeeeeeeeeeeeee 37 6. Determination of gallons per hour processed ......... 39 9. Power input deteminationfl eeeeeeeeeeeeeeeeeeeeeeeeee 39 f. Checking of the cut-in and cut-out temperature of the solenoid 8 B. mom OF PASTEIRIZATION .0900....00....OOOOOOOOOOOOOOOOOOOO 1. mu supply OOOOOOOOOOOODOCO0.0.0....OOOOOOOOOIOOOOOOOOOO a. @1188. creme” OOOOOOOOOOOOOOOO0.000000000000000000 b. 10038.1 creme” OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO... 2. washing 0.00.00.00.000.0..COO...OOOOOOOOOOOOOOOOOOOOOO... 3. Smtiung 00......0.00.00...0.00.00.00.00...0.0.0.0000... 5 t 5&88 B 4. ”.mtion 00.00.000.00...OOOOOOOOOOOOOOOOOOOOCOOOOOOOOOOO i 6’ mam OFWTES'PING eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee l .p. (a 1. Chmcal 0.0.00.0...O....0.000000000000000IOOOOOOO00.... 8. Ania-1t, OOOOOOOOOOOOO0.00.00...OOOOOOOOOOOOOOOOOOOOO b. Phosphate-8. OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO 2. Pmsical O00......OO0......OOOOOOOOOOOOOOOOOO0.0.00.0... a. cram ling .OOOOOOOOOOOOOOC0.0.0....OOOOOOOOOOOOO... b. flavor 0.00.00.00.00.0.0.0.0000....OOOOOOOOOOOOOOOOO 3e Bact9n01081°al eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee a. Tatal count eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee be TthOdmc eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee 0e ThemOPhilic eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee d. 0011me OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO..00... 3 Etttt $38 5&3 RmTS .OOOOOOOOOOOO0.0.00000000000000000000000000000000000000000000 A. ‘PASTEURIZATION'OF SALINE SOLUTION USING ORIGINAL EQUIPMENT ..., IF 0 0...... .I‘ —_-—————.——.,_._——_«'——‘ 1. 2. 3. 4. 5. 6. 7. 8. Time required to heat water to pasteurization tmporam.. .C..............C....0..................... Effect of an increased voltage on time required to heat saline solution to pasteurization temperatures ......... Influence of change in rate of flow on holding time ... Influence of changes in pump head on changes in holding tm. OOOOOOOOOOOOOOOOOO000......OOOOOOOOOOOOOOOOOOOOOOOO Ocnparieon of holding times as detemined with a can- nercial eoldnébridge with the holding times found with a mmad. m1‘u‘bflds. eeeeeeeeeeeeeeeeeeeeeeeeeeeeeee Revolutions per minute of single speed centrifugal pump. Revolutions per'minnte of single speed agitator ........ Influence of directions of flow on the capacity of the pastmrizer 0......0.0.0.0....OOOOOOOOOOOOOOOOO...0.0... he“. 2 0....00.0.0.0...OOOOOOOOOOOOOOOOOOOO0.0.0.0.... B. PASI'IDRIZATION 0F MILK USING ORIGINAL EQUIPMENT ................ 1. 2. 3. 4. 5. 6. Operation .............................................. Oreaming ability ....................................... Flavor ................................................. Acidity of milk ........................................ Phosphatase ............................................ mot.nologi°al t.8ta 0.0.0.0...OOOOOOOOOOOOOOOOOOOOOOOO c. PASTEURIZATION 0}! MILK SUBSTITUTING A VARIABLE SPEED PUMP IN E OMGINAL mm .000.0.9.000000.000.000.000....0000..0000 l. 2. 3.' 4. 5. 6. Operation 00......OOOOOOOOOOOOOOOOOO0.0.000...O...0.0... cram-ins ability OOOOOOOOOOOOOOOOOO0.0....0.00.00.00.00. new]? COCOOOOOOOOOOOOOOOOOOO0.00.00.00.00.000000000000. Acidity eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee Phoaphntase eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee BactQflOIOgCal tests 0.00....OOOOOOOOOOOOOOOO.9.0.0.... page 4'? 49 51 52 53 53 53 83888 M 05 ..... ...... ...... ...... ..... IIIIII ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... OOOOOOOOO ......... ......... IIIIIIIII ......... ......... IIIIIIIII ......... ......... OOOOOOOOO ......... 000000000 ......... OOOOOOOOO IIIIIIII ...... eeeeee eeeeee eeeeeee eeeeee eeeeee eeeeeee eeeeeee eeeeeee eeeeeee eeeeeee eeeeeee eeeeeee eeeeeee eeeeeee eeeeeee eeeeeee eeeeeee eeeeeee eeeeeee eeeeeee eeeeeee eeeeeee eeeeeee eeeeeee eeeeeee eeeeeee eeeeeee eeeeeee eeeeeee eeeeeee eeeeeee eeeeeee ....... eeeeeee eeeeeee eeeeeee eeeeeee eeeeeee IIIIIII D. F. G. DISCUSSION PASTEURILATION’OB'MILK'USING A.MAUKESHAJPOSITIVE.PUMP AND AN mm mm Pm“ 00....OOOOOOOOOOOOOCOOICOOOOOOOOOOOOOO l. substituting new equipment in original pasteurizer ..... 2. Balding time 0.0.0.0000...-6......OOOOOOOOOOOOOOOOOOOOO. rim. 3 0.0.0....OOOOOOOOOOOOOO0.0.0.0....OOOOOOOOOO... 3e Pound! per hour pmcessad eeeeeeeeeeeeeeeeeeeeeeeeeeeeee PASTEURIZATION'OF'HILK USING REDESIGNED EQUIPMENT WITH THE PW AS m mm me COOCOOOOOOOCOCOOOOOOO00.0.00... 1. Operation .............................................. Figure 4 ............................................... 2. Creaming ability ....................................... 3. Ilavor ................................................. 4. Acidity of:milk ........................................ 5. Phosphatase ............................................ 6. Bacteriological tests .................................. a. Total count ...................................... be ThOmOdmc and themophilic organlms eeeeeeeeeee 00 0°11me organiflnfi eeeeeeeeeeeeeeeeeeeeeeeeeeeeeee PAS‘I‘HJRIZATION or MILK $013an A ELIDING BOX FOR m Pm“ m WON. mNTmL 0..00.0.00.0000000000000000000.0000 1e Operation eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee ammo»: or MILK USING THE PADILE m: oomaox. AND A mm“ srABmm 00.00.0000.000000.00000000000000000000000. 1. Opomtion OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOCQOOOO “gar. 5 0.0.0.000...OOOOOOOOOOOOO0.00.0.0000...00...... ”8‘1” 6 0.0.0.0.0...0.0.00000000000000000COOO0.00...... 0.00.00...OOOOOOIOOOO'OO0.0.0000000COOOOOOOOOOOOOO0..0...... l. IPasteurization ofhmilk using original equipment ........ 2. IPasteurization of milk substituting a variable speed pump for the original tri-clever centrifugal pump ...... 8. Pasteurization of’milk using a Wankesha positive pump and an Cleatrioal Contml paddl. eeeeeeeeeeeeeeeeeeeeeee P889 56 57 58 59 59 59 61 62 62 62 63 63 63 63 64 64 65 65 65 67 IIIIII ...... OOOOOO ...... ...... ........ ........ IIIIIIII .......... OOOOOOOOO ......... ......... 0000000000 ......... .......... OOOOOOOOO OOOOOOOOOO .......... .......... OOOOOOOOOO ......... ......... OOOOOOOOO .......... .......... OOOOOOOOOO ......... ......... ...... oooooo ...... ........................ OOOOOOOOOOOOOOOOOOOOOOOO OOOOOOOOOOOOOOOOOOOOOOOO ....................... OOOOOOOOOOOOOOOOOOOOOOOO P389 4. Pasteurization of milk using redesigned equipment with the paddle as the electrical control ..................... 73 5. Pasteurization of milk substituting a sliding box for the paddle in electrical control ......................... 74 6. Pasteurization of milk using the paddle type control and a ”519581109 Stabilizer OOOOOOOOOOOOOOOOOOOOOO00....0.00.. 75 8 7. “at W paatmz. 0.0.0.0....0..OOOOOOOOOOOOOOOOOOOOOOCOO 8. The efficiency of pasteurization was compared in the ex- perimental high-tnperature short-tine pasteurizer with the holding paStmflur eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee I‘m 9. Conparison of experimental pasteurizer to a large steam Opent.d ”9:01.81 fled-.1 Oeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee 77 m 0..O...OOOOOOOOOOOOOOOCOQOOOOOOOOOOOOOOOOIOOOOOOOOOOOOOOOOOOOOOO % mm. 7 COOOOOOOOOOOOOOOOOOOO0.0.000000000000000000000000 8° Flame OOOOOOOOOOOOOOOOOOOOOO0....OOOOOOOOOOOCOOOOOOOOOO 81 figur.9 .OOOOOOOOOOOOO0.0...0.0...OOOOOOOOOOOOOOOOOOOOOOO 88 mm CITED .00....0OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO0.0.0.... 83 \ MXNO WENTS The author expresses his sincere appreciation to Dr. G. Malcoln.Trout for his kind advice and guidance during the entire period of this study and for his constructive criticisms in the organization of the manuscript. The writer also acknowledges with gratitude the guidance given.by'Professor.A. L. Bartree of the Bacteriology Department. Sincere thanks is expressed to Dr. Earl weaver for making this study possible and for the interest shown during the course of study. The suggestions offered by Professor J. 2!. Jensen are gratefully appreciated. The author also wishes to thank Professor J. R. Brunner for constructing the ”homeamade coldn- bridse' and for his views on the problems encountered in the study. Particularly is the author grateful to Messrs. Bailey, German and Alden, representatives of the Ex-cell-O Corporation, Pure Pak Division, Detroit,IKichigan, for giving their whole heared co- Operation throughout this study. illll [ llll‘llflll I I Ii 1 it Ill-Ill]! I'll. {ll-'11.! Design, Operation and Efficiency of a Producer Size Electro- pure Pasteurizer INTBDIIJGTION Iithim the past few years, the strides made toward acceptance of high-taperature, short-time pasteurization have been greater than at any other time in its history. Inch of the responsibility for the delay in de- velepent and acceptance of this systn of pasteurization, can be attrib- uted to the fact that accurate, sensitive, controlling devices were not perfected until recently. Obviously, accurate controls are necessary if the tmsperature of the mill: products is to be maintained within the desired limits; that is, sufficiently high to destroy all pathogens in the products and yet not so high as to alter appreciably the original characteristics of the milk. I lichigan now has a law which makes high-tesperature, short-time pasteurization legal. This law not only states the time and tmsperature required but also stipulates that ”acceptable equipment must be used.” Likely many types of short-time pasteurizers will find their way to the dairy market. Some of these may not be acceptable under lichigan's k new law. All of the pasteurizers on the market today are designed for large dairy plants since they are made to handle fun a minimum of 1300 pounds per hour to 80,000 pounds per hour. However, these pasteurizers may be either stems or electrically heated. The electrically heated and operated units may be suitable for the no.1]. producer who desires to process milk and milk products on his own dairy fun, but the capacities of the present ones are too great. A nsll producer size, electric pasteurizer has been designed and built by the liectre-pure Division of the lr-Oell-O corperatiern, De- troit, Iiehigsn. This pasteurizer was originally designed to handle 600 peundsgef milk per hour. he to the fact that an inediate need exists for a nail high- t-pereture, short-time pasteurizer on the dairy farm since steam gener- ally is not econmioelly available, it seued desirable that a detailed study be made of the producer size nectre-pure pasteurizer recently de- signed. W The investigation, involving large suple, long-time runs, ex- tending ever s period of 15 months, covered the following general areas: (s) the design of the machine; (b) various tesperature regulating devices; to) methods of operation; (1) capsi'ison ef the pasteurization efficiency of the lustre-pure pasteurizer with that of a mercial ate. operated high-temperature machine; (e) caparisom of the pasteurization efficiency of the some nectro-pure pasteuriser with that of a menial holder in- stallation and, (f) bacteriological, plwsicel and ch-icsl properties of the milk througbut the entire study. e I. i. — I) .l" llllllnlllll II|| iull II II! lllllll il.‘ l i.lll..|lllllu ll 11 .‘Ilellel l l. The chronological developent of the highotnperature short-tine pasteuriser goes back as far as 1886 at which tine the first high-tapere- ture shortotine pasteuriser was invented by Thiel, (anemone 1938). Ieig- mann (1893) described Thiel's apparatus as follows: 'It consisted of (a) an outer cylinder of tinned steel with a wooden Jacket, (b) an inner corru- gated cylinder closed at the bottm and nade of tinned capper, and (c) a hat shaped bod covering both cylinders. Between the outer and inner cyl- iader was a space for steel heating. A spiral agitator was attached at the tap." {his pasteurizer did not rmlain on the narket for any length of tine. Jensen, in 1901, (lacunae 1938) developed a type ef "flash" pasteuriner which lacked sufficient controls and, therefore, was not con- sidered a success. Beattie (1916) worked with a pasteurizer between the years 1913 end 1916, which .ployed electricity as the source of heat. The nature of the electricity was a high frequency eltemating current rangim between 8500 and 0000 volts. The apparatus consisted of a horisontal 'lethel' tube of glass through which still: flowed continuously, passing through copper electrodes, one at the niddle and one at each ad. Maroon and l'inkelstein (1919), studied high-tuperature short- tine electrical pasteurization using a machine which consisted of copper electrodes mounted inside porcelain cups. As the milk passed through a series of these cups the electrical circuit was capleted by the nilk, the resistance ef which was such that heat was generated. The mm of the pasteurization process was 153° 1'. which was reached by flowing milk preheated with ete- te 104° 1. over electrodes in the cape. Again, a high voltage of zone was .ployed. The amperage used on this copper elec- trode heater was 1d and the frequency 85. The high veltages were not only dangerous but also expensive. Bwever, Anderson and Iiakelstein (1919) concluded fre- their superinental work that 'Iodifications in construction met be made before the nachine can be considered a ee-eroial success.“ rhey also pointed out that an improved t-perature control was needed to assure uniform heating and to divert milk which had not been raised to the proper tnpcraturee herding (1921) reported that these porcelain cups, lustre-pare pasteurisere were in commercial operation in a milk plant located in Stan- ford, connecticut and also in Colubus, Ohio as early as 1914. is a result ef the findings ef Anderson and linkelstein (1919), this form of pasteuriner did not rush on the market for any length of tine. Yale (1933) reported that the next fern of llactro-pnl-e pasteur- iser was one in which the milk was heated by a OO-sycle alternating current ef zeo volts instead of by the higher voltage previously used. This pas- teal-deer, using milk preheated by steam to 130° to 145° 1., further heated the milk to no" r. This t-perature omeed a valve to open, the pen- mitting the milk to leave the machine. The pasteuriser was studied by Wilson (1983) and Harding (198)) of which reports will be made later. tale (1933) stated that the Pennsylvania Daparhent of health in- vestigated the Electra-pure process ef pasteurization in the year 1926. They wrked with a pasteuriner which was superior to all others since it contained two important imprevuents, 11¢er (a) constant level tank in- stalled to maintain a uniform head on the circulating pup and (b) an auto. matic nri stol'e teaperatue controller added to control the speed. of the nilk thereby regulating the taperature at which the milk was treated. They detenined the rate of flow of milk through the syst- and found that it tookrreacetealeeeondetorillac-gallenailkoaa. The holding time, or length of time required for the milk to pass fru the heated outlet to the cooler islet, was not determined. However, itlwas calculated to be from 3 to 4 seconds. This was essentially a ”flash" paeteariner. Dahlbcrg (1932) graphed the data of North and Park (1927), lar- unit and Dahlberg (1931) relative to the time and t-perature-necessery to render the milk safe yet preserve the are-ing ability. Il'he e-i- logarithic graph showed that 160° 1'. for 15 seconds provided a safety fac- tor of 5 seconds; while 14‘:. I. for so minutes allowed a safety factor of so minutes. i sinilar form of mantra-pure pasteuriner was studied by Ogden, carpenter and Darren (1924). The low York State Public Health Council ap- pointed representatives to study this machine which vat installed in the Cornell University Dairy Deparhnt. The machine operated as follows: The cold m milk was pimped through the regeneratcr while the hot pasteurized milk, flowing on the other side of the plates, was cooled. The raw milk entering was heated to about 120° 1. while the hot milk was cooled to about 90° 1. tree the regenerater the 120° 1. milk flowed through the filter cloth and flowed on up through the heater which consisted of two carbon electrodes separated by two pieces of glass. A hand operated micrometer valve, placed ahead of the heater was the only piece of equipent which con- trolled the tqerature of the milk. This form of control proved to be in- adequate einee the holding time also changed as the rate of flow changed which resulted in overholding of the milk since the maxim- flow as set by the valve had to be at least 15 seconds. Any position other than maxim opening caused the milk to be overheld. Up to this time inadequate controls did not effectively maintain the exposure time of the milk or mount of heat generated by the passage of electricity into the milk. Therefore, it was rightfully called ”flash“ pas- tearization. Iran the year 1927, high-taperature short-time pasteurization be- en *0 “"109 rapidly. The next fun of Electra-pare pasteuriner was studied cooperative- ly in 1927 by the low York State Departmmit of Health and the new York City Departaent of Health with the United States Public Health 8ervioe as re- ported by Yale (1933). The unit studied was a standard oo-ercial machine which contained an automatic thew-electric device for stopping the milk pup if the taperature of the heated milk dropped below the desired safe t-perature pOint. The l-gth of the milk piping leading frm the heater te the cooler inlet was twice as long as the one studied by the Puneylvania state health Depart-ant (Yale 1933) . Thus the length of the pipe tree the heater to the cooler section was 14 feet. The holding time betwen the heater outlet end the cooler inlet ranged between 11.1 and 19.7 seconds. is a result of extensive research by both the United States Public health Service and Pennsylvania Deparhent of Health the State of Pennsyl- ‘nnia was the first to adopt and accept highét-porature short-time eled- triccl pasteurization. This was in the year 1927, enctly 15 years after the process was introduced into the United States fru England (anonymous 1953) . ‘ Ieinreieh (1945) stated that in England, the linietry of Health stipulates 168.6" I. for 15 seconds as high-taperature short-tine pas- tourination. niece: (1945) pointed out that the 15-second holding tine (with a tuperature of 71.l° 0.) was chosen because it was a convenient holding time, that is, '10ng enough for controls to respond, yet short enough to penit a continuous floI.‘ wednredeh (1945) further stated that canary has the most com- plicated require-eat for short-time processing which consists of: coatined heating tree lee-159.90 r. in eevea seconds, holding at 169.9° r. for one second, cooling to 162.5" I. in five seconds and holding five more uecnda. Scandinavian countries designated 1a.? r. for 15 seconds as m m pasteurization, while 1%" r. to 135° 1. for a few seconds as high- taped-stare processing. Ira these tine-taperature requiruente of foreign countries it is evident that the high-t-perature short-time processing is much more rigorous than that required for the same processing in the United States. Blland and Dahlberg (1940) plotted at various time and tapere- ture combinations, the percentage destruction of LED» destruction of pbsphatase, and entmit of are. line reduction. In. their results they concluded that heating milk to 110° 1. without any holding would give th- all the desirable characteristics of pasteurization standards. The following is a description of the equipmt need with the Electra-pure pasteurizer of a few years ago. This material was obtained firm a private “Compilation of Studies and Tests on the Electra-pure Process” a copy of which was obtained from the Moll-C Corporation, Pure— Pek Division, Detroit, lichigan. The apparatus consisted of a (a) apply or surge tank for holding the raw milk; (b) regenerative cooler; (c) mul- tiple speed motor driven milk m; (d) milk filter; (e) electric heating ch-ber, and (f) electric control switchboard. Besides these were thermostatic controls, miscellaneous equip- ment , and instruents for antuatic operation, nergency shutdown, and for making tnperature recordings of pasteurization. The main units, with the emception of the electric heating chamber, consisted of standard pasteurining equipment. The electrical heater was the main unit for heating the milk to the desired t-perature, and consisted of a rectangular vertical chnber 24 inches high and 3 inches by 4 inches inside cross section. Two sides of the chuber were caposed of carbon electrodes separated by hard rubber in- sulators so arranged as to hold the electrodes 3 inches apart. The rubber insulators fened the other two sides of the chamber. In the operation of this equipent, the milk was drawn by means ofthepupfrathe eapplytenkandthroughtheupperhalfoftheregen- orative cooler. In this regenerate:- the cold raw milk at approximately 40° 1'. (at? 0.) passed upward through the inside of the pipes where it was gradually heated to approximately 185° to 130° 1'. (51.6" to can" 0.) by heat exchange with the treated hot milk which one an the electric heater and flowed don over the outside of the rage-orator tubes. This inter- change of heat units reduced the mount of heating in the electric heater and also the uncut of cooling in the entire process. The static pressure of the raw milk flowing within the regenerator tubes was purposely made to be below a‘hosphsric pressure, which surrounded the outside of the cane tubes, so that in case of an leaks in the tubes there would be an inward flow of treated nilk into the raw nilk, instead of the raw milk flowing in- to the pasteurized milk and contaninating it. Iron the nppenost coil of the regqioratcr where the nilk had attained a taperetme of approzinataly 125° to 130° 1. (51.5“ to 54.4" a.) , the milk was dram by the pulp and forced through the twin filter. The latter was designed to r-ove all foreign natter such as dirt, etc., which suetines fond its way into the milk. A fine neeh filter cloth (60 threads to the inch) effected this motel as the milk passed through. The appara- tus was equipped with two filters, one of which could be taken out of service tuporarily for cleaning, without interferring with continuous operation of the process. Ira the filter the nilk passed over to the treating chnber where in passing usardly, it was subjected to the action of an alternating our- rant (so cycles) at 220 volts between electrodes. lore the taperature ef the lilk was raised to any predetermined value for which the nachine was set to operate. One mdred and sixty degrees rahrenhsit (71.0“ G.) was the usual conercial practice. Leaving the electric heater, the nilk passed over to the tap por- tion of the regaerative cooler. here it spilled down and over the outside of the tubes, giving up its heat to the raw nilk within the tubes until it reached the brine cooled tubes in the lower half of the regenerative cooler. In this lower half of the cooler, the Iilk was finally cooled to approxi- nataly 30° to 88° 1'. (2.2“ - s.a° 0.). 'i'he t-penture of the nilk leaving the electric heetei- was dependent upon the rate of new of the nilk strean -10- passing up between the electrodes. Since the flow of electric current, which passed transversely through the colon of milk betweui electrodes, was dependent largely upon the elctric conductivity of the nilk which with- in the usual operating range was practically constant, it would be apparent that the lower the velocity of milk and the longer the exposure to the electric current flow, the hotter the milk would beccno, and vice versa. i'he rate ef flow was dependmit upon the pup speed. Iith the apparatus set for an predetoninod tcperature, the operation was absolutely autuatic by means of the thenostatic control devices connected with and regulating the speed of the motor drinks m. by operation tending toward too high a t-peratnre was offset by a speeding up of the m notor and any tudenoy towardtoelowatqperaturewasmet with a slowingdcwnof thep-pmotcr. If, for any reason, the t-perature of the treated milk fell be- low the lowest tolerable value for tich the apparatuslwas set, the control devices out off instantly the electric apply circuit to the pup motor, thereby stOpping the pup and the flow of the milk. 8- WWW .‘ here are two types of high-tapereture short-time pasteuriners en the market, one .ploying electricity as the source of heat and control; the other utilizing steu to heat the milk and acupressed air as the con- troller activator. 'l'he pasteurizer with the electric heating unit is made up of a constant level raw nilk tank, a positive pup, plate regeneratcr, carbon electrode heating chub er, holding tubes or sections, diversion value, in- dicating and recording theme-stars. The heating chamber consists of a two foot section nade up of glass on two sides and carbon electrodes on the other two sides. Il‘he in- side of the chanber is three inches wide and four inches long. he elec- trodes in this chamber are three inches apart. it each and are porcelain insulators which prevent the electricity fraa grounding on the natal parts of the machine. Feller (1944) described the nacho-pure equipment, other than the heater, which makes up the large, omercisl high-taperaturo short- tine pasteurizer as follows: - 'l. The ballast tank, which regulates the flow of raw nilk to the unit free the supply tank, insures a constant head on the nilk pump." '2. Attached is another driven positive type nilk pm which sucks the raw nilk through the regenerator and pushes it through the rest of the cyst- at a steady constant flow.” '8. A tubular blding section designed and engineered to accom- plish the required holding period. This is located between the heating chsnber and the diversion valve.“ '4. A diversion valve consists of a long "tooled" stun, with a ground lead at one end and a restriction four inches away from the same and. It is operated by an electrical necrotic coil mounted at the top of the diversion valve. " '6. Located between the diversion valve and the cooler is a set of plates so constructed as to allow cold, raw nilk to be named by the pasteurized hot nilk going to the cooler. This flow diversion valve is controlled by a recording themeter located at the farthest and of the holding tube.“ -12- lilbert (194.5) pointed out that the reason dairynen are anxious to adopt high-t-porature short-tine processing was because 80 percent of the heat was recovered and therefore 80 percent less refrigeration was needed. He stated that: “9° 1‘. raw milk ... regenerator ... so porcuit recovery since raw milk is preheated to 138° r.' an" I. pasteurized ... regenerator ... 80 percent recovery since the pasteurized nilk is cooled to 64° 1. before it enters the cooler.” Palmer (1944) noted that this type of valve was introduced by I. s. rie1der in 1927, but was not used with high-taupemture short-tine equip- nent until 1939 when the contact themeter was discarded. This theme- ter controlled the nilk pup rather than the direction of the flow as the diversion valve does. Olson (1946) gave a ccnplete description of Operation of con- trolling instruents used with the steanitype installations. The operation of these instrumts and the source of heat energy are the only differences between the two types of pasteurizers. Olson (1946) explained the usual controlling instruments as follows: '1. i mercury-irglass indicating thernonotor located in the milk line between the and of the holder tube and the flow diversion valve. This themeter unlike similar instruments used for 30 minutes holding systans hasaverycpenscalewitharangeeflso" “1650!. audio graduate in one-half degree divisions.' '3. A stem pressure controller, for maintaining a constant lup- ply of stea- to the diaphraa valve of the water t-perature control under conditions of forward flow.’ -13- '0. A taperature controller for nainteining the circulating water at the correct value." '1). A safety thenal recorder which serves three functions: (a) Provides record of temperatures of nilk leaving the holder tubes; (b) electro-pnematically actuates flew diversion valve; and (a) records whether flow diver- sion valve is in forward flow or diverted flow posi- tion, depending on whether bulb of safety thermal limit recorder is above or below the desired out-out tapereture.“ Ieinreich (196) reported that since 1937, 75 percent of the nilk processed in hrope was pasteurized in high-taperature short-tine equip-ant. Gillespie (1944) outlined the maintenance and operation of steel pasteurizere. no remanded that a routine neintenance schedule should be followed prior to daily runs to check the accuracy of the pasteurizing equip- nent so that it Iould operate efficimtly throughout the processing of the dairy products. Iain-ion (ruse) painted out that no difference existed between the tee types of pasteurizer as to efficiency of pasteurization, because of the source of heat. Iran his description it appears that the steel high- tqperature short-tile pasteurizer is nuch like the Electra-pure short-tine equipent except for the source of heat used. W The nethod for checking the lag of themeters and the setting of the flow diversion valve is erplicityly described in the 'lilk Ordi- nance and Gode', Bulletin ‘80, United States Public Health Service. -1g- Hall (1945) stated that lewton's Law of Cooling should be applied to figure the lag of a thorns-star when it is in a surrounding of a differ- ent t-perature than itself, the fonula being: a a -— 7‘34) dt t : Tile in seconds i' = ruperature of surroundings R 2 Themet or reading it : Lag constant of thenmter The checking of holding tine is accaeplished by two nethods, nanely, the color nethod and the 'sol-u-bridge' nethod, which is preferred. Rishoi (1946) stated that the nethod of injecting color solutions into the holding section and the l-second interval sampling at the end of the holding tube for presence of the dye was too ”sluggish” for accurate» results. no remanded the use of the 'solvu-bridge" and a stop watch since electrical responses were better than the physical stinuli of the color appearance. mshoi (1946) described a 'hoIe-nade sol-u-bridge' using a gal- meter and a double throw switch. With this he used the second hand of his wrist watch and found that it gave him fairly accurate results. Ieber (1945) eonpered the 'sol-u-bridge' and the gelvanoeeter assnbly and discovered the difference to be measurable. selt (194.3) calculated the volt-e of the holder tube and con- verted this to rate of flow per hour. Oohn (1946) illustrated sole of the problem he encountered in checking high-taperature short-tine equipent. he points out the prob- lus that arose and the subsequent solutions he applied to tha. Ball (1943) stated that the preheating tine should not be over- looked in comparing 145° 1'. for so minutes to no to 161° 1. for is to 16 seconds since as nuch as 50 percent of bacterial reduction is ac- -15- cenplished during this period. The total tine involved in processing canned foods was considered in the sterili nation process and therefore we should consider it in the pasteurization process. mace: and Davis (1943) concluded that the nargin of safety was not yet established accurately for the therature, tine ccnbination of 160 to 161° 1. for 15 seconds, because laboratory equipnent was lacking which could reproduce the rate of heating and the short holding of conercial units. Warring: Galoin, albumin and other constituents of nilk treated by high- tnperature short-tine pasteurization develop a deposit (nilkstone) which is difficult to r-ove. loore (19“) stated that the type of deposit present on short-tine equip-ant one quite different in conpositicn from that encountered on holder pasteurisers. He spoke of a double treatment nilkstone mover which is now universally adopted. Iith these treat-ants brushing is salda necessary since the deposits are rqoved very efficiently by pulping the cleaning so- lutions. The cleaners are composed of wetting agents, cmpounds which have flocculating and peptonizing properties. One of the cleaners is acidic in nature, while the other is basic. Ii‘rout (1946) concluded that it apparently nade no difference which treatnent was first, the alkaline or acid, as some workers used the acid treatlent shile others used the alkaline treatment first, with equal suc- cess. Bell and Sanders (1944) reported that the reaction of nilkstone in a high-t-perature short-tine heater was greatly decreased by preheating nilk, skim milk and whey. -15- WW Prior to introducing an nilk into the pasteurizing equipent it is inerative that the entire apparatus should be sterilized. Cavanaugh (1946) stated that the canon practice of sterilization is carried on by circulating hot water at a taper-stare of 180° or 190° 1‘. for five to fifteen ninntes through the caplete syst. and then to fill the systu with chlorine-water solution, allowing the solution to stand about five ninutes when it is forced out by the first run of nilk. Another nethcd, he advised, was to sterilize by using hot (1” - 190° 1!.) water only and allowing it to circulate about fifteen minutes. He ream-ended the inspecting and checking of equipment be nade while circulating the hot water or sanitizing solution. During this taparature checking, it was advisable to check the sanitary pipe Joints for leaks, especially on the nilk suction side as a leakage would considerably upset pup perfcnaances. relay (1934) stated that after the equipment was sterilized and inspected, the raw nilk was allowed to flow into the cyst- via constant level tank. The cold, raw nilk was ”sucked“ into the systu and during the pasteurization process cooled the cut-going pasteurized nilk. This part of the process is called “regenerationJ' Getchel (1935) working with electric pasteurizers, found that after the nilk was preheated it should be ”pushed“ instead of "sucked” in- to the heater section, if a constant voice and unifon holding is to be naintained. . Mart (1945) stated that plate heat exchangers have been fore- nest in the rapid adoption of high-tauporature short-tine pasteurization in that they allow the notuent of nilk in a thin filn at a rapid velocity and thus have the nilk at the critical heat for a nininu length of tine. -17- Putnan (1945) believed that the reason high-tauperature short-tine processing was so successful was because of the flow diversion valve as well as the regenerative feature. button (1940) realized the progress that was being nade in the de- sign and use of autaatic controls on high—tanperaturo short-tine equipment. He believed that autmatic controls should be installed on holder equiprent. The phaical and chemical changes brought about as a result of high-taperature short-tine pasteurization have been observed and studied by nany workers. W Anderson and Pinkelstein (1919) checked raw and Electro-pure treated nilk for titratable acidity and found that after 84 hours the raw nilk showed a high acidity, while the treated nilk showed a slight decrease in acidity. The raw nilk curdled after 24 hours and had a ”pin-holed" ap- pearance, while the treated nilk mained nomel. After 48 hours, the acidity of the treated nilk increased to the point where the nilk curdled; this curd unlike the raw nilk curd was normal in texture and appearance. High-tauperature short-tine pasteurization is nore efficient in preserving the original vitnin content of nilk. lioness et a1. (194.5) pasteurized acne nilk in a stainless steel vat which they assayed. They reads this study to detemine whether there was any reduction of vitamin con- tent due to short-tine pasteurization. They obtained the following results: Vitnin i Raw In. :1 :fi'auri 2g; Ascorbic acid ; 16.4 ng/L. : 16.6 ad!“ Riboflavin : 1.5 ng/L. E 1.5 Ig/L. main 3 W -18- In another experiment, Hones ettal. (1943) assayed sale nilk, treated by the holder method, for wits-in content and found the following: ’- um than WW Ascorbic acid ; 19.1 wg/L. : 15.9 ng/L. Riboflavin ; 1.5 Ig/L. ; 1.43 lg/L. Thinin : 0.33 leg/L. : 0.50 lgflu Iillenky and Brueckner (1941) found nilk which had been pasteur- ized by the high-terporaturo short-tint method after 5-days storage, had a higher ascorbic acid than that processed by the long hold method. W The cross line on a bottle of standard nilk is an important sell- ing point since the sustaeer believes that the value of cream is a measure of 'riehness' or butter-fat content of the milk. Therefore, the dairynan will be anxious to buy and use only processing equiment which will naintain this creel line until the attitude of the custmer changes. fielton and Sewer (1944) found that there appeared to be no dif- ference in the nanner in which the areas layer fence on raw nilk as ou- pared with pasteurized 111k. ' Bauer (1916) studied the crooning ability of nilk and found the fat packs together more so at roa taperatures than at ice water tapere- tures. He says that the difference in specific gravity on the fat and the serus at the two said tesperaturee accounts for the shallower cream line at roan t-peratures. mm (1898) and others, indicated that for best results of ores- ing, the nilk sample should be placed in ice water during the rising period. -19.. Iilbourue (1922) reported that tanperature of pasteurization effected creasing ability since he observed wide ranges in cream layer foraation. He thought this was due to natural causes or inadequate tas- perature controls. He recon-ended 142° 1‘. for 30 aimtes as the pasteur- ization standard. Dean (1927) found that the anount of cream rising on will: pas- teurized by a continuous flow electrical process (using a standard piece of menial equipent) was ocnpared with that rising on the acne lots of nilk pasteurized by the vet with circulating water as the heating nedia. The average for six trials gave cream values as follows: Pasteurized by electricity .......... 14.5 percent Pasteurized by vat nethod ........... 13.0 percent Rawailk (no treatment) ............. 16.3 percent Price (1922) reported that dreaming was injured at 14.99 r. if held for so ainutes. ae advocated 112° to 145° 1. for so minutes as a standard pasteurization. Anderson and Iinkelstein (1919) concluded that the nectro-pure process in no way interfered with the creae line in milk treated at 70° 0. W Inseam and trout (1940) found that high-tusperature short-tine processing produced nilk which not only had a higher initial score but also kept a higher score than the holder (aerated and nonserated) treated after 6 days storage. They reported as follows: :0 Days Storage :6 Days Storagc ...!‘nsm = m = 4.92:1... Raw : 21.80 : 20.99 Bolder: : : Aerated 3 21.81 : 21.34 Honaerated 3 21.86 3 20.45 High-taperature short- : 22.16 : 21.56 til. M — They also noted that less oxidized flavor was encountered in highrtenpera- tore short-tine pasteurized link. Sharp, Trent and Guthrie (1936) explained that the effect of high temperatures of pasteurization in retarding the development of oxidized flavor and the destruction of ascorbic acid could be explained by scanning the destruction of enzyees, which if present accelerated these changes, and that these enmes survived pasteurization at no“ 1'. Although Quinn and Burgweld (1933) found that the high-taperatnre short-tine pasteurization imparted lass ”cooked" flavor to the milk than did the holder method, it nust not be overlooked that "cooked” flavor is nore apt to develop if controls are only slightly off which.would allow tampere- turee to go a little above pasteurization teaperatures since the safety range is shorter than.in.holder'pasteurizaticn. Gould and.Selaer’(l939) attributed cooked flavor to the formation of sulfides which occur when nilk is subjected to sufficiently high tapere- tures or to other changes occurring sinultaneously with this fanatics. larwrdt and Dahlberg (1934) showed that heated flavor was in- parted to cram acre readily than to nilk. 'rhey separated and churned the cross and found that heated flavor was associated with fat:aore than with the serun. Dahlberg, et a1. (194.1) studied ”quick tine” pasteurization and found that the nilk heated to 169° F. to 177.5" 1'. was of slightly better quality. The exposure tine above 140° 1. was fro-.6 to 24 seconds. 'They concluded also that 110° 1'. with a controlled rate of heating is a good possibility for future pasteurization tines. Pasteurization reduces the bacterial flora in silk and thereby increases the tine prior to putrefaction and off flavor development pro- vided the nilk is stored at low tupcratures. Shenan, et a1. (1933) found that pasteurized nilk showed a 1ower perceuteg. of growth when stored at 99° 1. (0° 0.) than raw nilk. Anderson and Finkeletein (1919) found that high-temperature short- tine pasteurized nilk had good keeping qualities for about 6 days at 6 to 10° 0. (41-600 1'.) which are merciei storage temperatures. Pasteurization is not above the naxinua taperature for treauaent of nilk for cheddar cheese production. Phillips (1928) found that a naxinun flash t-perature of 168° 1'. nay be used in heating the nilk for the nonu- facture of cheddar cheese. mgher taperetures gave a weak body and texture, a scorched flavor and soaetiaes allowed a bitter flavor to develop. W oversea (1945) found that the ash content of nilk was lower be- tween lay and October and that lactose was highest during the smaller. latsuo (1929) studied effect of heating on constituents of nilk and found that (a) casein fraction increased; (b) albuin decreased to a were trace, and that (c) globulin decreased by so percent. Bell (1926) found that ccaparable anounts of calciu and phospho- rus were rancved free solution at 110° 1. is heated raw skin nilk 60 min- utes and obtained suples at 10° intervals between 150° 1'. and 2120 1. leg» and Harvey (1926) suggested that heat changes the calcite salts of silk frua a soluble to a colloidal fen. Ferric hydroxide (Ie(OH)3) was used and the results showed no reaction with the “denatured” calciu. Gould (1946) found that ulfhydryl groups were formed in ailk which was heated to 168° 1'. through 212° 1'. The groups were antioxidants and re- sisted subsequent oxidation. The phosphatase test is used today to detemine proper pasteur- izatioa procedures. Kay and Grahm (1926) develOpcd the phosphatase test. dilcreas and Davis (1926) substituted color standards and expressed anount of phosphatase as ng. of phenol per 0.5 .1. of nilk. The naxiwua enount of phenol considered as pasteurized nilk was 0.037 ag. lslaquist (1932) used a modified Kay and Graham phosphatase test, incubating the couples for 24 hours. Bock (1942) found a thermophilic organi- which survived pasteur- ization and which produced phosphatase in the pasteurized nilk which whn tested for presence of phosphatase was naturally positive. This inplied erroneously that the nilk was not properly pasteurized. Boner (1946) pointed out that the greater presence of ascorbic acid in high-taperature short-tine treated nilk caused the phosphatase to react acre completely and thus a darker blue color resulted. W ll'he ability of a pasteurizer to destroy all pathogenic bacteria and at the ease tine nduce the nonpathogenic population, is acre inportant than physical or clinical changes it inparts to the milk. Therefore, the percentage reduction of bacteria as well as the final count of the treated nilk is of value when evaluating the efficiency of any pasteurizer. Carpenter (1929) found that it did not nake any difference as to the source of heat used in pasteurization since heat produced by an electric current effectively destroyed tubercle bacilli found in raw nilk. o -.- Stone (1909) studied the influence of electricity on micro- organins and found that high voltages were lethal, while low voltages were stimulating to the organi no. Andersen and linkelstein (1919) found that the percentage of bac- terial reduction was at least 98.7 percent. The raw nilk samples of the first series of the test were excellent containing only 150,000 organises per nilliliter. This nilk was pasteurized down to 12,000 organins per nilliliter. lhen the nilk was poor to begin with, (12,000,000) the nilk pasteurized down to 155,000 colonies per nilliliter. There are two schools of thought as to the reason for such effi- ciency in reducing the total bacterial population in nilk. Beattie and Lewis (1925) worked with electrical pasteurization and believed tint the organi-s were killed by the electrical current since the t-perature of the treatnent was lower than the thensl death points of the organi-s. Gelpi (1931) found that there was another factor other than heat which was involved in llactro-pure pasteurization. He found that bacterial spores were nore efficiently destroyed in his electrical pasteurizer than in the holder trials even though the t-perature of either trea‘haent was not lethal. Tracy (1932) desenstrated by passing an alternating current through grape Juice containing yeast cell suspensions that a pronounced killing took place even though the tnperature of the exposure was only 42° c.(107.s° 1.). Anderson and linkelstein (1919) believed otherwise for they said that “The destruction of bacteria in the nests-pure process is apparently due to the heat produced by the electric current rather than to the electric current itself." lendorf (1938) did acne work which agreed with the finding of Anderson and rinkalstein. W Minn (1942) defines tho thenoduric bacteria as those that with- stand either of the pasteurization taperatures, 145° 1. for so ninutes or 160° to 1610 for 15 seconds. Both the “long hold“ and short-tine pasteurization exposures are abnonal t-peratures for the thencdurie erganieu. It sens logical to expect high thencdurie counts in high-tapersture short-tine treated nilk since the square to this abncnaal tuperature is only a few seconds. Ew- ever, humor and front (1928) worked with yellow cocci which they isolated fro. dairy products and found than to withstand taperatures of 30° c. for 30 ninutes. In (192.1) stated that it tho flora is resistant to pasteuriza- tion the possible destruction during pasteurization is nil. Therefore, the probl- of ”pin-point” colonies on plated nilk suplee indicates that pro- Iducers are neglith in proper sanitation and that they should practice better housekeeping otherwise this nilk would not he pasteurized down to legal linits especially if it were processed in high-tesperature short- tine equipent. moan (1940) reviewed tho literature on thencduric bacteria found in pasteurized nilk. labian (194.2) stated that nore thencduries are apt to be found in the high-t-perature short-tine process than in tho holder process. Isle and Kelly (1033) concluded that high-teaporaturs short-tine pasteurization was not as efficient in reducing bacterial counts of nilk as was the holder nethcd. This was due to the fact that the bacterial flora was of a resistant nature. 'rioa-an and Scanner (1940) reported that counts were higher with high-t-peratui'e short-tine oqnipwant than with long holding (vat) ti-oat- nents because of thenoduric cont-instion of the nilk utmsils. Sue have tried to I'piza down” the source of these organins. The source is still greatly undetenined as these organi-s are found every- where. Dctterer (1945) pointed out that the source of the themeduric organi-e in nilk could be traced to the producer. 0'Dsniel (1942) checked the producers with the idea of reducing thenoduric organi-s in the nilk. He was able in this way to increase the pasteurization efficiency by nine percent. Lovowita (19cc) fend, in average herds, that tho neen thernoduric population was three thousand per nilliliter. This was not the case in certified herds, however. Jensen and Berti-es (1946) were nore specific for when they studied the nilking nachine and its inflations with tin idea of determining the nest suitable nethod of washing and sanitizing it, they found that by frequent boiling of tho rubber inflations in a strong man (lye or sedit- wanna) it was possible to reduce the total thenoduric population to a standard which was desirable. Robertson, ot a1. {1923) studied pasteurizing oqnipnont and found that]. man. I. around-Wanda. M00131“)- 1:0- 1ated from dirty eguiput showing nilkstone fornation. xii-an (194.1) reported that certain species of nicrococcus caused high bacteria counts in will: pasteurized by high-taperature short-tine equip- nent. These organi-s were nest often themodurics and could be isolated fre- dirty, neglected lilting equipment, especially nilking nachines. -25- maker (1928) found a prolific umber of nicrocecci in pasteurized mill: samples. He found that nest of the thermoduric organims found in. nilk are the nicrocecci. Curran and Evans (1945) found that heat activated spores of the resistant organism and thus upon standing such nilk would increase in count, especially if the nilk was a 145° F. lyers and Pence (1941) worked up a simplified procedure for the laboratory era-inatien and control of raw nilk supplies. lerris (1943) found that the resazurin test alone was a good neth- od for detemining the amber of themoduric organims. Iainess (1941) stated tint new that high-taperature short-tine pasteurization was being used acre and nore, laboratory controls rust also be brought np-te-date since ordinary laboratory tests used today are not efficient to detect themoduric organise in raw nilk supplies. Be recon- nends the resasurin test for quick, econenical laboratory control. breed (1928) favored the aicrescepe to supplement plate counting when checking producers for themodurics. loll-am, et a1. (1940) proposed a nanmm acceptable nunber of 40,000 themeduric organise, as detected by the nicroscepic technique, in producer's nilk. Breed (was) found that tho causes for high themend and theme- pbilie counts are: (a) repasteurizatien; (b) tuperary ”tie up” of pasteur- ized milk (14301.); and (c) hotwells used in pcwdering nilk processes. Robertson (1927a) concluded that young, rapidly growing or ade- 1escent cells are more susceptible than the older cells to the killing action of high taperatures. As the tenperatures used approached the themel death points of the organins, the degree of killing at any one age -2'I- is greater and extends over a longer period of tine. If the greatest effi- ciency ef pasteurization of nilk or canning of foods is desired thui heat should be applied to the product before the microorganisms have passed the accelerativa growth stage. W Robertson (192'!) cited 44? references on thencphiles and thenc- durics and gave an excellent review on the subject. lodge (1930) made a fine study of the life cycle'of a themepbilic organih. Brannon and Prucba (1927) found that in pasteurized nilk (62.9 0.) high counts were due to nonspore forning organism. This was not conclusive for they felt that further investigation should be made. Tanner (1944) pointed out that themophilic bacteria survived t.- perstures as high as 16° 0. (167° 1.). Robertson (1927a) isolated species of therlepbiles and therleduric organics fun nilk and found that their rate of growth, except for a. m:- m 3573’ relatively slow at taperatures ranging between 20° 0. through 39° 0. Breed and Prickett (1929) reported that sens themophiles isolated from nilk were found to be liquifiers, alkali producers, and others produced acid. They felt that thenopbiles are not connected with insanitary prac- tices. The themephiles are not considered to be pathogenic and therefore are not a health hazard, only a dairy plant nuisance. Fabian (1942) stated that more problus with thencphilas are apt to arise in holder pasteurization than in high-temperature short-tine process- ins. WW Californ organi-s have the ability of fernenting the lactose in nilk. Il'heir presence in raw nilk is' of no significance since pasteuriza- tion kills virtually 100 percent of these organisms, (Pinkelstein 1919). Hears”, at al. (1932) used the ooliforn organius in pasteuriza- tion efficiency studies and found that sole survived pasteurization. Ayers and Johnson (1924) studied W my, and found that at 155° 1'. for 50 ninutes the “majority" were killed while at 150° 1., or above, for 30 ninutes exposure he obtained the "absolute“ death point or 100 percent kill. Beams (1930) emined 100 pasteurized nilk smples and found that 52 percent of th. contained Whig-W organise. He found tho majority theme]. doath point of W m to be 144° 1'. for 50 ninutes. Start and Patterson (1956) reported that of 505 cultures studied they found that less than one percent survived 143° r. for so minutes. They concluded that coliforn organics in pasteurized nilk were due to post-pasteurization cont-inetion, and nay, therefore, be an excellent nethod of checking the efficiency of pasteurization. This was especially true in high-taperature short-tine processing since this nethod virtually destroys all of the organins. Dahlberg (1946) found that if one out of three deaexycholate agar plates or one out of three brilliant green bile tubes, were positive, it did not necessarily loan that the ample was positive for 3. an; be du- plicated results only when two out of the three plates or tubes were pontifle *t‘ ... .-.,5 .. noes-e. -29- Speck (1947) plated some milk sanplea which he inoculated with I. m and which were heated to 140° 1'. for 50 minutes. Other emples were treated at 140° 1'. for 55 minutes. Snell red colonies appeared on the desoxycholate lactose agar, which were less than one nillineter in diameter, on the 50 limits plates, while no colonies were evident on the 55 minute treatnent. l. W was the organist isolated from the 50 ninnte exposure plates, since the n. my. did not survive tho 140° 1. for so nin- utes. Speck concluded that this organic night be aployed as the test organic for proper pasteurization. ligh-tmperature short-tine pasteurization is a safe netbod of processing since the W W is destroyed during processing. sonqnist (1952) found W m was killed at 1eo° r. in 11 seconds. Andersen and Finkelstein (1919) stated that “the flsctro-pure nacbine does not affect appreciably the physical and chemical properties of nilk, reduce the total bacteria count satisfactorily and at the sons tine destroys nearly all lactose fenenting, Inde positive organinns in raw nilk.” Robinson (1923), Dowd, et a1. (1943), and Erwin (1945) studied high-tanperature short-tine pasteuri nation and found favorable results. Devereaux (1929) after working with nectro-fira pasteurization, concluded “that the convenience and simplicity of the machine and the efficient nanner in which it reduces bacterial pepulations and destroys pathogenic organise in nilk without altering the taste or creaning ability of nilk asks the nectro-pure process one worthy of further consideration by the producer, the consmer, and the investigator of dairy products.” MAI. mam A. PWZATION W The high-taperature short-tins pasteurization was con- ducted throughout this study with a new model of an electric pasteurizer which was called ”producer size'l since it was designed for the mall pro- ducer. The parts used, listed in Table l, are designated with correspond- ing letters as shown in Zl'igure 1. Table 1. A list ef parts that couprised the original pasteuri zer at Tri~c1ever centrifugal pup nectar-pure heater Thermal thermometer Hetering valve Holding section Hercury thermometer Recording thermometer cable Solenoid (electric coil) ‘l’low diversion valve Recording thermometer (volt meter upper left) rereward flow pipe Diverting flow pipe Agitator Surface cooler container for pasteurized nilk Raw nilk surge tank valve Raw nilk surge tank DHOIIHH ~HHNOHHUOUP l'igure 1 shows the original installation which consisted of the necessary heating and cooling parts but which lacked efficient controls. Tho list of the parts ccnpri sing the original ”producer size” pasteurizer are described as follows: -31- wjifl‘“ .41‘w . ,, Showing the original Electra-pure, producer size pasteurizer. Figure 1. a. W The surge tank (Q) was 4 feet in diameter and about 3 feet deep. It was made of stainless steel natal and had a capacity of 50 gallons. A 2-inch outlet was located on the side and near the bottom of the tank. b. mug All piping was made of stainless steel metal with tin soldered flanges and ferrals. The pipes were 1 inch in diameter with the exception of the holding tube which was originally 2 inches in cross section. c. m Irhe surge tank valve (P) was made of white metal and was an ordinary two way type. The flow control valve (D) was also made of white natal. A groove was nade in the valve in such a nanner that nilk flowed even when the valve was placed in the eff position. This valve was the only source of taperature control in the original installation. line positions, spaced equally apart, were set on a wooden scale and nounted on the outside of the valve. The gallons per ninute were detemined in the various valve positions, both in diverted and foreward flows. d. m The first pup (A) used was a tri-clover single speed cea- trifugal pm, which is standard in the dairy plants. The revolutions per ninute were detemined. This type of pup operated by a 110 volt single phase actor. The second pup tried was a centrifugal type and was identical except that its speed was adjustable by means of a variable speed drive pulley. The third pup (not shown in figure 1) studied was a leukesha positive pup, driven through a variable speed drive. This pup proved de- sirable and efficient and therefore was retained in the redesigned producer size pasteurizer. e. m This tupcrary agitator (I) was part of the original equipcnt. It was installed to keep the creel portion of the silk well 45 --. c‘ .4. agitated and nixed throughout the nilk so accurate crean line determinations could be nade of the treated emples. f. M The heater (I) was 6 inches long and was made of two flat, carbon electrodes mounted opposite each other with two pieces of glass, 1 inch thick and 4. inches wide, separatiig thc. Il'he inner area of the chs-ber was 12 inches, since the size of the rectangle cross-section was 4 inches by 5 inches. These carbon electrodes and the glass sections were clamped together with flat pieces of netel bolted together. Above and below the heater were sections of porcelain which insulated the electrodes from the rest of the nachine. hall rubber tubing, which can be seen on the floor in back of the panel in fig.- 1, supplied the water needed to cool the elec- tredes. This tubing led into a pipe so arranged that water flowed down the back side of the twe carbcn electrodes. The function of this water was to cool the carbons and to wet the carbon surfaces so that even distribution of the electrical energy resulted. Two leads were located in back of the heater. These entered the heater fit. the back of the panel and were attached to a knife switch lo- cated on the back franc of the panel board. This smaller heater, of the two tried, required 240 volts, 60 cycles and 50 uperes in order that the nilk would be rapidly heated to the desired tuperature. After several runs and sane equipmt nodification a lit-inch heater was installed, which differed only in the length from the 6-inch heater. 'This required the changing of the voltage to 210 volts since the 10-inch heater would use more than 10 kilowatts per hour. Il'his would over load the line, not only in the Dairy Building but also in the rural areas which night adopt this pasteurizer. g. W 111 themmneters used were installed in the original nachine. Theme-later (0) was used to indicate the position at, which the valve was set. The thermal thermometer was kept at 130° 1". until all of the raw nilk was preheated (by diverting milk) to a tauperature which would give an exit t-perature of 130° 1'. or slightly higher. The valve position was then restricted so that the milk would go fairly rapidly into forward flow. This valve was never changed to a posi- tion which would show 165° F. or above on the themal thcmoneter. Ther- noneter (I) was a nercury in glass type which was calibrated from 140° 1'. to 212° 1. in i-degreesintervals with minimum spacings of 1/8 of an inch. This was used to check the operating taperature of the pasteurizer and the diversion valve was set according to this "naster' themcmcter. The ther- meter was nounted on the exit end of the holding section. Thermometer (I) was a Taylor recording thermometer with a tnperature and a diversion flow pal operating on the chart. Actuation took place at 1250 r. A volt- neter was located in the upper left corner. The inside of the recorder had both the pen an adjustnant and the flow diversion cut-in and cut-cut ad- Juehaent. The cable from the recorder extended under the panel section to the top of the holding tube or section where it was nounted near the ner cury thenoneter. h. M The solenoid labeled (I) in figure 1 was nade up of a wound coil with a square core to which was attached a square rod with a swivel end. The swivel end was attached to the end of the diversion valve. The coil had wires leading to the recording thenoneter which were attached to a cut-in switch, which in turn was activated by the setting of the re- cording thencneter. The solenoid and recording themcneters were both op- erated by a llO-volt alternating current. ...- i. W The at- of the diversion valve consisted of a long ”tooled” piece of netal which had a restricting washer nounted in such a way as to cause restriction only in .i'omarit flow position. This allowed the nilk to be heated nore rapidly since it slowed up the flow of the milk leaving the nilk in the heater for a longer period of tine. J. W In 18-inch by 24-inch tin coated copper surface (cooler was installed on a suitable franc which nade it portable. This dealer used tap water as the refrigerant. This refrigerant was capable of cooling the nilk down from 161° 1'. to 54° 1. (71.1“ c. to 12.2" c.). k. m Three switches were required with this equipent. The ene on the left of the electrical conduit (figure 1), was the pump switch; the one en the right operates the recording thermometer and voltneter. The third switch (not shown in Figure l) is the nain switch located on the back of the panel control. This is the heater switch. 1. W (l) W Two paddles, nade of rubber pressed onto a steel shaft, were tried. {niece were placed into the heater section and nounted in such a way as to allow the paddle to be nanually operated in a pivoting nanner, by a handle located on top of the heater and attached to the steel shaft. lash of these paddles were used separately and each was different. One had a solid rubber facing tapered at the sides and at the end and was 1* inches wide and 14 inches long. The second was six inches from the bottcn. These paddles were used since it was found that electrical input could be cautioned easier than the flow of the nilk since the electrical input does not affect the holding tine while the rate of flow does. (2) W A phenolic resinous box was constructed so that it would snugly but loosely fit into the heater. Three holes (5)8 inches in digmeter) were drilled and a shaft mas mounted in the center of the block. The box moved up and down between the electrodes with the movanent of the steel shaft. (3) Begistangg atabilizg: The stabilizer was made of a section of ordinary pipe which was cut from an ordinary pipe, 1 inch in diameter. Around this was a heavy number 8 wire coiled in such a manner as to leave two Open ends. A cut-in and cut-out relay was attached to the open end of the coil and this in turn was out into the heater circuit; the other end of the coil wire was attached to the main line. The stabilizer would cut in and out every ten to fifteen seconds, as was evident on the second volt- meter attached to the resistance section. The extent of cut-in and cut-out was detemined by the thermostat setting. As is indicated on the record- ing thermometer chart, the stabilizer controlled the taperature to within one degree of the 161° setting. The stabilizer was not part of the original equipsent and was installed much later in the experiment when other means failed to control the temperature rise. n. W Two different holding sections were used, one with the centrifugal pmnps and the other with the positive pump. The difference was in the cross-section of the two tubes. Each modification or equipment substitution was made after several trial runs were made to determine the type of change needed. 2. W a. W The revolutions per minute of motors and pumps tested were made with a tachometer and a stop watch. -37- The tschsneter was a thumb type with a removable rubber nipple on the end for setting on end of shafts. The scale on the tycometer was divided into 100 parts which were divided in 10 parts which in turn were divided into 10 parts. Thus the smallest reading was 1 revolution per minute. The stop watch was a Oenco (Swiss) make which had its seconds divided into one-fifths of a second. Two workers were required for the deteninstions of revolutions per minute, since it was necessary to watch the number of times the revolving bead traversed around the scale. The revolutions were clocked for 1 minute intervals. The number of times the bead traveled around the scale multiplied by 100, plus the fraction of 100, timed for 1 minute, constituted the revolutions per minute of the nortor or pulp tested. be W The mercury and room-dine thor- mmeters were checked according to methods outlined in 1111: Ordinance and Oode" Bulletin zoo, United States Public Health Service. The floating thermometers in the raw tank or the thermal thermom- eter were not checked. However, their respective tuperatures were compared to the mercury themneter when immersed in hot water, e sufficient time being allewed fer themometers to equalize. e. W The holding time was detemined by observing an electrical inpulse. A *eol-u-bridge' was made using a gel- monster, double throw knife switch, number 12 insulated copper wire. re- sistance cell of salt and rubber steppers with e piece of cepper and iron wire pierced through than. The pierced rubber stoppers with the wires through thu constituted the probes, one of which was mounted in place of the mercury themeter; the other was placed in a special apparatus. The special apparatus was made identical to that in Iigure 1, located between the lower end of the holding tube and the metering valve, except that a mall nipple was welded to the side. Thus the probes were located just above and i-ediately below the holding tube. Two leads were connected to each probe, the other ends of the lands were connected to the galvancmeter through a double switch. This made two complete circuits, one being at each probe. The themal themeter was rssoved and a nut with a brass washer was used to hold down a 1/8 inch thick rubber diaphragm This diaphrag was easily pierced with a 80 gauge needle attached to a‘ 50-miniliter syringe. Saturated salt solution was made using ordinary table salt. A Oeneo (Swiss) stop watch, graduated in 1/5 seconds, was used to time the interval between the galvanoneter deflections. Iater was placed in the raw milk surge tank to its fullest ca- pacity. The milk pulp was started and the water was allowed to flow for a time (five ninutes or more). The syringe, with the 20 gauge needle attached, was filled with saturated salt solution, then the point of the needle was forced through the rubber cord diaphrap. The operator of the stop watch noted the galvanoleter deflections while. another operator injected the salt solution. As the salt solution passed the first probe, the deflection of the galvanoneter was noticed and the stop watch was started and the knife switch thrown to the other circuit. The deflection in the galvanometer was again noted what the salt solution passed the second probe at which tinethe thing was stopped. The time interval between the galvanoneter deflections constituted the holding time. The holding time was tried with various valve positions which were calculated in gallons per minute. a. W The gallons per hour were determined by weighing the milk that was pumped through the pasteur- iser and over the cooler in a given tine. A zi-geiion milk can was weighed without the cover. The nilk flowed through the heater and holding tube on out the flow diversion valve (forced shut) and through the forward flow pipe and finally over the cooler for souetime before the weighed can was placed and the timing started. A steady flow continued for some time before the can was placed under the de- livery spout below the cooler. The timing was started simultaneously with the placing ef the weighed can under the spent. The nilk was allowed to flow for five minutes before the can was renoved and weighed. The initial weigh (weight of the son) was subtracted from the final weight. The final weight was multiplied by 12, since 5 minutes is a twelfth of an hour. The product of this multiplication constituted the pounds that the pasteurizer was able to process in a period of one hour. e. W An smmeter was used to determine the kilowatt consumption per hour of operation. The uperage consumed never exceeded 50 at any time but was less than 50 during initial preheating periods. The kilowatt consmption was detemined by the following female: II : 1.1.3.111 1000 Ihen II 2 kilowatts Y : volts A . amperes P3 = power factor Note: In this instance, since the load is non-reactive, the power factor = l. The t-perature registered on the mercury themometer was the criterion for the cut-in and cut-out taperature of the solenoid which in turn controlled the position of the flow diversion valve. This was done according to the methods outlined in "Milk Ordi- nance and Code“ mlletin 280, United States Public Health Service. If the cut-in taperature was too low or too high then the adjusting "wheel” lo- cated inside of the Taylor recording themometer was adjusted until the de- sired cut-in temperature (161’ r.) and the cut-out temperature (161° 1.) ”I. obtained. 3. PIDCEWRE OF PASTERIZATION W a. W [ilk used in the initial runs and in the runs of final testing of the producer size pasteurizer, was obtained from the College Oremery in ten-gallon cans. The college Greenery obtained its milk frm its own producers or from a local dairy. Later, when the machine controls were redesigned and perfected, comparisons of efficiencies with those of vat (holder) pasteurization and a large ccuercial high-tuperature short-time pasteurizer were made. The milk that was used for comparison of efficiency of pasteuriza- tion with the holder was obtained by the following method: A EGO-gallon vat was filled to capacity, and after sufficient agitation, a 30- to ail-gallon sample was obtained. The snpling pail used was washed and than sanitized with 200 p.p.n. or more available chlorine solution. Rubber gloves were worn to minimize possible contamination while sampling. After the 30- or dO-gallon sasple was taken, a' .all, sterile sanpler was used to bbtain sufficient sample for bacteriological and phosphatase test. The bacterio- logical seeples and phosphatase samples were placed in test tubes and stored in ice water until analyzed. b. M The milk that was used for the studies of relative efficiencies of the mull experimental llectro-pnre pasteurizer and a large menial, stems-heated, high-t-perature short-time pasteurizer, was ob- tained by exchanging 40 gallons with a local dairy which had the large coe- meroiel unit installed recently. This gave a representative sample since the 40 gallons obtained was from the sale supply tank that feeds the surge tank of the commercial pasteuri zer. The 40 gallons was mediately shipped to the Gollege Greenery where it was pasteurized. Samples were taken of the milk treated in the commercial short-time pasteurizer for bacteriological, crenline, phosphatase, and flavor studies. W All parts of the machine were disassaabled and washed prior to making a run. lach section of equip-neat was washed and brushed with water at 13) to 150° 1. (4.9.3 to 55.5° 0.). Suitable detergent or soap was used ‘ to give washing properties for ease of milk film rasovel. After washing the sections and parts, warm water was used to rinse the equipment. The equipent was then allowed to drain dry. then dry, it was assaubled. M then the equip-ant was assubled, as shown in Figure 1, cold water was hosed into the surge tank and sufficient m, or other chlorine bearing compound, added to give at least 200 p.p.n. of available chlorine. This was allowed to circulate fer about 10 to 15 minutes by pimping. Ihile the chlorine water was circulating, the end of the diversion flow pipe was stoppered with the palm of the hand to force the sanitizing solution through the forward flow pipe and over the surface cooler. lhen the 15 nimtes were up, wan water with a tuperature close to 140° 1’. was added to the surge tank after the chlorine water was drained. This wan water not only rinsed the chlorine out but also warned the piping and other equipmt of the pasteuriaer. Lm Raw nilk in ten-gallon cans was duped into the surge tank. This tank fed the centrifugal map which pumped the nilk through the whirl- pool agitator located on the bottom of the heating unit, and forced it on up to the tOp of the heater. At the tap of the heater (to the left) was located a themeter which registered the taperature of the preheated an. m. taperature was 130° 1. (ce.5° 0.), m1. the nilk was divert- ing and waning in the raw nilk surge tank. This operation continued until the tuperature of the .111: in the raw nilk tank reached so to 100° 1. (26.6 to 37.1“ 0.). After the raw nilk in the surge tank was up to the re- quired preheated t-perature the metering valve was closed to retard the flow through the heater to such an extent that the nilk was heated fit: 80 to 100° 1'. on up to 161° 1'. Iron the heater, on past the thenal thenc- eter, and the netering valve, the nilk entered the holding tube whose vol- .e was such that 16 seconds were required for the nilk to pass through it. The nilk leaving the holding tube passed the mercury thenoneter, which registered the tuperature in one-half degree-“gradations from which it sinultaneously passed the recording thenoneter cable. The t-perature recorded by the recording thenoneter either caused the nilk to be diverted or passed on to forward flow depending on whether its t-perature was above or below 161° 1'. This was acccnplished since the recording pen an was set in such a nanner that when a certain set tuperature was reached, (160° 1.), contacts closed, causing the solenoid to close the diversion valve. This forced the nilk to fill up the diversion chamber and spill out into the forward flow pipe from which it flowed down over an 18 by 24 inch surface cooler. The refrigerant in the surface cooler was ordinary tap water which cooled the milk from 161° 1'. to 54° F. (71.1" o. - 12.2“ c.) c. ETIQCEWRE 0]? W Tm W a. m The acidity of the milk, before and after treatment, was determined by pipetting 9 milliliters of milk into a white porcelain cup after which five drops of phenolphthalein was added. This nixture was then titrated with Hafis reagent (l/IO sodim hydroxide) to a faint pink color. The graduations were then read and the readings were the percent of lactic acid. b. M The phosphatase test was made by following the field test nethod as outlined in "Standard lethods for the Examination of Dairy Products," 8th edition, 1941. LEW a. W The milk smples for this determination were left in ice water fro- the time they were taken until they were read. Samples were obtained from the raw supply tank, diverted flow outlet and at the outlet below the surface cooler. The raw milk sanples were heated to 100 to 120° 1'. ($7.? to 68.8° C.) nonentarily to repeal: the fat globules, otherwise a larger cremlline would be observed in the pasteurized samples. All san- ples were placed in 100 nilliliter graduated cylinders with a little alco- holic suspension of Sudan III dye; Reassurin was found to be equally good in differentiating the cream line on 84 hour settings. Cotton plugs were placed on the cylinders to observe creen plug formation. These were then stored in the refrigerator at 40° 1. Samples were most always read at 24 hours but occasionally at 48 hours. b. M The flavor of the raw and treated samples was determined by the dairy staff members who did the tasting and criticizing. lo attmpt was nade to actually give each sample a particular score. The pasteurized nilk was tested throughout the various runs for any off-flavors that might have develOped during processing. W a. W Total counts were made on all samples by the dilution nethod. After the dilutions were node senples were plated by use of a pipette. After the required mount of sample was placed into the petri dishes (obtained from the media room) the agar was poured. The media used was standard tryptose glucose extract with sterile skin nilk added at the rate of 2 milliliters per 300 milliliters of medium. Ho akin milk was added to agar which was poured into plates having dilutions of 1/10 or less since sufficient nilkawas already present in these dilutions. After these plates hardened they were inverted and incubated at 57° c. (98.60 F.) for 4.8 hours. After the 48 hour incubation period the plates were counted. b. W3 Themoduric organims were those which survived pas- teurization t-peratures. Practically all of the themoduric organisms appeared as pin-point colonies on tryptose glucose extract nediu after 49 hours of incubation at 37° 0. The nethod of plating was the sane as outlined in "Standard Methods of Milk Analysis," 8th edition, 19a. o. W For the thermOphilic and themoduric studies samples were obtained from producers who were known to have a prolific amount of these organisms in their nilk due to poor practices. These were pasteurized in the sons nanner as regular nomal milk. The samples were plated and treated as outlined in "Standard Methods of Milk Analysis", 8th edition, 1941. The plates were incubated at 560 I. for 48 hours after which they were read. Growth at se°”r. indicated thermophilic organises. d. m Tests for number of coliforn organisms were made by plating dilutions and pouring the plates with deserycholate agar which is selective of colifona organises. Desoxycholate plates were prepared by introducing 1 n1. or .1 ado. quantities of nilk into the petri dishes and pouring the plates. After the nediun had solidified a second layer of three to four nilliliters of desoxycholate was poured on the surface to prevent develcpnant of atypical colonies. The red colored colonies, ap- pearing between the two layers of desoncholate after 18 to 20 hours incu- bation, were considered to be the coliforn organises. RESETS A. PASPRJRIZATIOH 0F SALINE SOLUTION USING ORIGINAL EQUIPMENT Since experience in operating the producer size mectro-pure pasteurizer was desired, water instead of milk was pasteurized. A neter- ing valve, which contmlled the flow of the water was the nethod of tee- lperature control in the first runs. Salt (an electrolyte) was added at the rate of 80.5 grams per 80 gallons of water. This made a 0.21 percent saline solution which exhibited the sue conductivity as silk when placed in the path of the heater electrodes. The original saline solution tas- parature was 53° 1'. The voltage varied fron 203 to 205 volts during the first six runs. A 6-inch heater was used. Table 2 illustrates the tine required to preheat the saline solution prior to going into forward flow. Table 2. Rate of preheating of saline solution prior to forward flow when using 803 volts 3 T-perature of saline solution in Elapsed tine 3 M : z z 0 x 71 3 57 3 65 10 : 82 z 66 : 1‘ so : 93 z 75 z 65 30 x 103 : 86 x 94 40 x 115 z 94 : 104 50 z 124 z 104 : 112 60 z 133 : 113 z 121 N x 143 x 122 z 131 so a 154* : lac : 140 90 z x 138 x 149 95 : : 141?."I x 153* *I’orward flow. o..- —a- -47- The data indicate that entirely too much time was required to pre- heat the saline eolution to a taperature which would pannit forward flow of the saline solution. When the saline solution in the surge tank was heated sufficiently high to permit forward flow, about 142 to 155° 1., the pasteurizer then was able to bring the tusperaturo up to the required 100° 1'. Thus, it would soon that the original voltage was entirely too low to permit successful operation of the pasteurizer. .-. . _..,‘_,.;. ,. .. . a. . ._;; A -t .. W Two transformers, each having a load capacity of five kilowatts, were installed to step up the voltage fron 205 to 240. Together they allowed a load of 10 kilowatts per hour to be consumed with no overloading of the power lines. The data are presented in Table 5. Table 3. Rate of preheating of saline solution prior to forward flow when using 240 volts : Tuperature of saline solution in Elapsed x at L° I.) : w tine W W 3 ALE L 2.3.... 3 z z 0 : es : 73 : es 5 : 04* x as : 'n 10 z 96* z 96 t 06 12 x -- x 102* z -- 15 : 102‘“ t 102* x 90* *Forward flow. Th0” late show that the preheating time was only five ninutes prior to rel-ward flow when the tank temporatnr. was 68° 1. and the nachine was pasteurizing 0.6 gallons per minute. The raw tank toaperature kept ris- ing while the saline solution was in forward flow, this being due to a leak .. H- u -- in the flow diversion valve. The data show also that nore time was re- quired to preheat the saline solution prior to forward flow tauperature when 0.8 gallons were pasteurized, even though the initial saline solution tauperature was higher, (Table 3). Since changes in valve positions resulted in a corresponding change in the gallons per ninute processed, it sewed desirable to note the effect on the holding time. The data are presented in Table 4. Table 4. The holding tins of pasteurization is in- fluenced by the position of the valve Val" 3W Wail—W : z x l 3 33.2 : 33.6 8 33.6 2 : 29.0 3 29.2 a 29.0 a 3 25.4 : 25.6 : 25.6 4 : 22.4 P. 22.4 x 22.4 5 : 21.2 x 21.4 : 21.6 6 : 19.2 : 19.2 : 19.4 7 : 18.2 : 18.0 x 18.2 8 3 17.2 : 17.4 x 17.0 9 x 16.0 : 16.2 : 16.3 When a recheck of holding time was made a two second difference was noted even though conditions were the same in both runs, except the water level in the raw tank. Therefore, it was thought that head pressure on the centrifugal pump caused this difference. Table 5 illustrates the holding tine differences due to changes in head pressure on the pulp. -49- Table 5. Changes in holding time due to head pressure changes on the centrifugal pump Valve : Holding time 3 Difference in P08536101! :___Lsmnds)____=.hnldins_ma_ 9 3 18.0 8 16.0 : 2.0 9 : 18.6 x 16.2 : 2.4 9 x 18.6 : 16.3 x 2.3 9 x 18.8 : 16.0 x 2.8 A hone-nade sol-u-bridge, as described by Rishoi (1941) , was con- pared to a eel-ercial model BB5, manufactured by Industrial Instruments, Inc., Jersey City, New Jersey. The results of holding tine deteminations by the hue-nade apparatus and with the R03 instrument are given in Table 6. Table 6. The eonparison of holding tine deteminations made by the lune-made sol-u-bridge with the 1215 commercial sol-u-bridge Valve 3 Holding tine (seconds) :Differences in position zWMmoldins tin- e . t z : z 1 : 32.3 : 33.3 : -l.0 seconds 2 : 31.0 : 29.1 : 1.9 " 3 x 26.1 : 25.4 : 0. 7 " 4 : 23.6 x 22.4 x 0.8 " 5 6 28.8 3 21.4 3 le‘ ' 6 : m.6 : 19.2 : 1.4 " 7 : 13.2 : 18.1 : 0.1 " 8 6 1,02 ' ‘ 17e“ 3 43.2 " 9 x 11.0 : 16.1 x 0.9 " The data indicated that the response in the hone-made sol-u-bridge was slower in all but two positions, those being practically the two extras P081 tionle The speed of the centrifugal punp was detemined. The data are P"Mt.d in Tabl. 1e Table 7. The revolutions per ninute made by the tri- clover single speed centrifugal pulp lumber of : Seconds : Revolutions .nnlniim = W : z . 790 z 30 z 1580 800 : 50 x 1600 1595 x 60 : 1595 805 x 30 z 1610 The speed of the tri—clover pups was relatively fast. With such speeds and recirculation of nail]: for 15 minutes, churning might be expected to take place. W The speed of the nilk agitator was determined. The data are re- corded in Table 8. Table 8. Revolutions per minute nade by the nilk agitator Revolutions : linutes ; w : slanted—.... 3 30 x 0.5 30 : 0.5 62 z 1.0 60 x 1.0 60 : 1.0 The revolutions per ninute of the agitator were 20 (Table 8). This relatively slow speed was insufficient to cause shaming. -51- The gallons per minute processed was determined in both the for- ward and diverted flows while in the same valve position. are in Table 9. Table 9. Data obtained A comparison of the volumes delivered at the same valve positions while the cysts: was in diverted and forward flows J now : Position : , : :Difference in quantity WWW“:— : z z : Diverted : 1 : 2380 : .629 : Forward . : 1 z 1960 3. .518 z 580 '1' Diverted : 2 8 2870 x .759 : ' Iorward : 2 x 2250 x .595 : “3° '1' Diverted x 3 : 3400 x .883 : romre : s x 2550 a .674 3 95° ‘1‘ Inverted : 4 x 3700 x .978 : {award 3 4 z 2700 x .714 : LOGO ‘1' Diverted z 5 z 4360 x 1.152 3 Forward : g x 2900 : . 765 : 1,460 '1’ Diverted x 6 1 5100 x 1.35 3 Forward 3 6 z 3060 x .814 z 2’0“ ‘1‘ ' Diverted : 7 z 5940 x 1.57 T : l'orward : 7 z 3250 x .859 x 2'5” '1‘ Divorted : 8 : 7260 : 1.92 3 Forward 3 8 z 3350 x .886 x 3,910 ‘1' Diverted : 9 x 7660 x 2.03 2 forward : 9 x 3400 x .899 : 4,260 ‘1' It can be seen fro- the data presented in Table 9 that the vol- use of nilk treated per hour depended on the position of the valve. The rate of flow in forward direction varied from that in diverted direction by as little as 580 ale. to as such as 4,260 ale. which represented a dif- ference in volme of 29.5 to 125.2 percent respectively. This neant that the saline solution (or nilk) was retained in the heater 1/7 to 2 times as long as when in diverted flow, even though the valve position and voltage .e~.o ‘ . - - .1. o C D O —-—..- .7, O -. .. . . C , . .- - I - .- -- . "<.~-*-~ - ..- ... .... -- O v . o , - e - , . a 7..- ...—.-. - O , . _ c . .- . c ‘ . s . < . - o—v...“ ... ~—- av-., - . F. . - .- or heat input was not ehanged. Therefore, the tuperature of the saline solution (or nilk) should be expected to rise rapidly, depending on valve position, when the pasteurizer suddenly goes into forward flow. The recording chart (Figure 2) shows that the above deduction was eorrect since the t-perature rose continually after the saline solution went into forward flow. A restriction caused by a washer being welded on to the at- of the diversion valve formed a collar which slowed up the flow when the saline was in forward flow. Iigure 2. showing the rapid rise in tuperature after the saline solution went into forward flow. 1. Forward flow 2. Diverted flow -53- B. PASTERIZATIOH 0? MILK USING ORIGINAL EQUIPIIEM' mm Data obtained on the operation of the machine when milk was used are given in Table 10. Table 10. A typical m using the original equipment, 240 volts, and nilk Elapsed tine x Taperatureoof : Direction : Valve 2 : a 0 x 68 : Diverted : 6.0 5 : 78 : Diverted : 6.0 10 : 85 : Forward 3 4.5 15 x 85 : Forward : 5.0 20 z 84 : Diverted : 5.5 85 3 ’0 3 ram 6 6.0 30 z 92 1 Forward : 7.0 35 x 92 : rorward : 7.5 40 z 91 : Diverted : 6.0 The data show that the valve control was not adequate enough since the flow of the nilk would change quicker than the operator could respond to the chuging taperatures. This lag in response to tapers- tures caused the nilk to go from diverted to forward and so on until the valve position was set Just right by trial and error. After 10 ninutes of forward flow the silk diverted; then after going back in forward flow, the nilk diverted again after 15 ninutes of pasteurizing. W The crean line was determined since butter granules appeared in the raw nilk tank after nilk had been in forward flow. The amount of cream line reduction that took place due to churning action is shown in Table 11. Table 11. The creasing ability of the processed nilk testing 3.6 percent butterfat 3 Treatment 3 Tina , 3 W _ Sanp1e 3Tneperature= Operating: : : Percent amber : (01.) : win.) : giuilitgrsf;Percent : Reduction __ : z - z z z 1 : 68 : 0 2 16.0 : 100.0 : 0.0 2 x 130 z 5 : 15.0 : 93.8 : 6.2 3 z 160 z 10 z 8.5 : 53.1 x 46.9 4 x 161 z 15 x 8.0 x 50.0 1 50.0 5 : 163 : 20 x 8.0 : 50.0 x 50.0 6 z 165 x 25 x 8.0 x 50.0 a 50.0 W Flavor deteminations were made on samples of the milk taken throughout the entire run. Cooked flavor was found in samples which were treated at 165° 1‘. or higher. The samples treated at 160° to 163° F. were excellent in flavor. WW Only sanples which had an acidity of 0.15 to 0.18 percent were used. The acidity of the milk drapped from 0.002 to 0.01 percent as a result of pasteurization. W All pasteurized couples were negative since they all tested less than tvzo units. The raw milk samples tested more than five units and were therefore definitely positive. Wigwam Bacteriological tests were made but were not reported here since the taperature controls were not perfect at the time these runs were made. There was, however, 99.9 percent reduction in bacteria population but this is not significant since there was definitely signs of overholding. —- ore-e --.- . a e o ....- .—- .- . r . e --. . ‘ e~~- an m - 55 - c. rimuplygggg pg: gag-vsppsggpimc A VARIABLE _S§EED PUMP IN THE ORIGINAL EQUIPMENT am The operating equipnent was similar except the speed of the pump was varied. Speeds of 1080, 1266 and 1520 revolutions per minute were tried. When the pump was set to revolve at 1080 and 1266 revolutions per minute, the operation had to he stepped since the tanperature of the 1111: could not be controlled. Whine: Table 11 illustrated that as much as 50 percent creamline was re- duced during pasteurization. It was also stated previously that butterfat granules appeared in the surge tank while the milk was in diverted flow. The speed of the pump was thought to be the cause of this loss due to churn- ing action. Table 12 illustrates the extent of creanline loss when the speed of the pup was slowed down to 1520 revolutions per minute. Table 12. Greening ability of milk when determinations using variable speed pump set at 1520 revolutions per minute 3 Treatment = Time = We _ Sample 3tunperature30perating= 3 3 Percent = ° : Mini)- ,5aiuiiiiorai-hnmi__annnioa__.x o : : : z x 1 z 62 : 0 : 13.0 : 100.0 x 0.0 2 z 130 : 5 : 12.5 : 92.5 : 7.7 3 z 160 : 10 x 7.5 3 57.8 i 42.2 4 z 163 z 15 x 7.0 a 53.9 x 46.1 3L__11s:n:: The flavor of the milk was detemined from time to time during processing. Cooked flavor was found in practically all of the pasteurized suples. This was thought to be caused by the increase in holding time due to the fact that the variable Speed pump was set to make 2'70 less revolu- tions per minute. W The acidity of the milk was lowered due to pasteurization. This was the same as in the previous trials. All nilk which tested 0.19 percent or lore was not used. Was: The phosphatase test showed five units or more for the raw samples and lore than two but less than five units in the diverted samples. All of the seaples obtained while the systun was in forward flow had a phosphatase test of less than two units. Thus the raw and diverted samples had a posi- tive phosphatase while the pasteurized samples had a negative phosphatase. Mama. Bacteriological tests are not recorded even though aseptically taken nilk saples were plated, since the cream line reduction was as se- vere as in the previous runs. D. WWW saggy; USING A W P081111; mm A__N_]_3_AN EECTRICAL CONTROL PADIIJ t t . a t Previous tests proved that varying the flow of the nilk was not a satisfactory method of controlling the treatment taperature. It was, therefore, thought that a more constant control could be had by varying the electrical input. This was done by installing a pivotally supported paddle having its axis at the intersection of the diagonals drawn between the corners of the chamber. By a control handle externally of the chamber the -57- paddle was turned parallel to the faces of the electrodes, thus resulting in greatest shielding and minimum power input or it was turned at right angles to the elctrodes resutling in minimum shielding and maximum power input. The paddle was mounted in the 19inch heater which was installed and which necessitated changing of the voltage back to 205 volts. A clamp type emmeter was attached around the incoming electrical power line. The position of the paddle was marked 1-10, the meter showed the greatest power consxmmtion when the paddle was set at 10. A Waukesha positive pup was installed in the redesigned equip- ment. The reason for the substitution was to obtain a constant volume at all times. The pump was adjusted to deliver milk at a rate that it would take 16 seconds for the milk to pass through the holding tube. Iith the new equipent being substituted in the original equip- ment, the variable speed pup, the thermal thermometer, and the metering valve were moved. The Iaukesha positive pump replaced the variable speed mp; a 212° F. indicating themometer replaced the metering valve, and a plug was placed in the place of the thermal thermometer. W The holding time was detemined, using the same equipment as was used in the previous determinations with the equipment shown in Figure 3. The speed reducer attached to the Waukesha pulp was adjusted by turning a round shaft which stuck outside of the housing. The holding time was taken and the adjustments made until the required 16 seconds retention was had. Since only ene position was now available, due to the ruoval of the meter- ing valve, no table was prepared to show the holding time determinations. J 'I ma l’l I ”III I | l LJ L. —————-—————"l —r- St’CT/OA/ HOLD/IVS —-." lh’iATt—‘R I SECTION! I f l l i now DIRECT/01V / 00061.5 T/mow sax/res Figure 5. The electrical hook-up and instruments used to determine the holding time. W The pounds of milk processed per hour was found by weighing the milk pasteurized during a five-minute period and multiplying by 12. The machine was found thus to pasteurize 35? pounds of milk per hour. 1;. 12mg; gown or m USING mom EQW WITH THE PADILE AS THE EECTBICM. 00% who Since the metering valve was discarded, the method of operation was changed entirely. The operation of the machine was as follows: After the machine was washed, reassqnbled and sanitized, raw milk was dulnped in- to the raw tank. With the agitator on, seaples were taken for bacterio- logical, physical and chemical analysis. The recording and pump switches were placed in the "ON" position. After a few minutes of milk circulation in the surge tank, the heater switch was turned on which energized the heater. The milk was allowed to circulate through the diverted flow until the surge tank tauperature was such that the heater was able to heat the milk to 161° E. which put the milk into forward flow. This was accomplished by moving the paddle handle to the number 10 position and observing the emmeter so that not more than 50 uperes would be used at any one time. lleanwhile, the 212° F. indicating thermometer (which replaced the metering valve) was observed so that at no time did the t-nperature go above 167° F. and then only occasionally did it go above 165° F. When the recording ther- mometer was recording a tauperature that was close to the cut-in point, the paddle position was reduced so that the tmnperature of the milk leaving the heater was very close to 165° F. The need for this extra 3 degrees was due to the fact that the holding section was of stainless steel and had no in- sulation around it. Therefore, in order to prevent the milk passing through thd holding section, from being cooled to below 161° 1. it was necessary to increase the heater exit tanperature of the milk. The heater exit thermometer was ob served continually throughout the entire operation to make sure the taperature of the milk did not get out of range. A record of the tanperatures that occurred throughout a run using this new taperature control is presented in Figure 4. ‘10 56 50 Figure 4. A record of a run made with an insulating paddle as the electrical control. 1. Adjusting the temperature controls. 2. Adding cold raw milk. 3. Went into diversion. Data of a typical run using the paddle control for maintaining the desired tenperature are given in Table 13. -51- Table 13. A typical run using the paddle control for maintaining the desired tanperature Iinutes :Surge tank : : :Heater exit :Control 22ers H125 tauperature j°flzVoltt£ez Imperesfiamerature CF) :__pcsition : z z z : 0 : 48 : 200 z 50 : 153 x 9.0 12 z 62 : 200 x 50 x 157 x 8.0 14 : 62 z 200 x 38 x 163 x 3.5 24 z 62 x : 35* z 165 x 3.5 200 *Iininun limit As can be seen in Figure 4, the temperature remained rather con-- stant throughout the entire run. The milk diverted only when colder milk was dqued into the surge tank. The data of Table 13 illustrate the rather low temperature required in the surge tank before the heater was able to place the milk in forward flow. The 200 volts was not intentional but was the result of other machinery being hooked up to the same 205-volts line. Since nilk offers less resistance when wam than when cold, the ampere consutnption was not able to go below 35; thus the tmpemture would rise sanewhat. The paddle had to be manually moved to a trifle lower posi- tion after the amperage ccnmnption was a little above 35 emperes. After two hours of operation the machine was disassunbled and the parts observed. The paddle had a caseous deposit on its edge. The de- posit seued to be the greatest near the upper portion of the paddle and en up to the inside of the heater outlet. hole. Woman Since the tunperature in the heater at the upper section was high enough to cause the casein to be deposited, it was thought that the cream- ing ability of the nilk was also injured. The extent of cream line destruc- tion when the paddle was used as the tauperature control is shown in Table 14. -32.. Table 14. The creaming ability of the processed milk testing 3.6 percent butterfat :Treatment = Operating 3 0W 7: Sample: temperature: time 3 z 8 Percent umber: (° F.) 3 (minutes) 3 nilliliters : Percent : reduction 1 : 48.0 : O z 18 : 100.0 : 0.0 2 x 62.0 : 12 : 16 x 88.! x 11.1 3 x 163.5 x 14 x 13 : 83.4 : 16.6 4 x 162.0 : 24 z 15 : 83.4 : 16.6 3 : 163.0 : 30 x 15 x 83. 4 x 16.6 The data show a 16.6 percent reduction in cream line. This loss is much less than the previous runs using other equipment but still it seued that if the “hot spot” in the heater could be eliminated the cream- ing ability of the milk would not be injured in the least and maximum crooning would result. W The flavor of the treated milk was excellent throughout the SO-gallon run. The cooked flavor of previous runs was not noticed unless the temperature went out of range, that is, above 163° 1. W Acidity was determined as a means of choosing nomal nilkeince milk containing an acidity which is higher than normal would heat duicker due to greater conductivity. Erroneous heating times would result since the average nilk has a normal acidity. ata lever in any of the previous runs or in the present runs, was there a positive phosphatase test in the pasteurized samples. Only the raw and diverted samples tested positive phosphatase. - 53 - W a. W The bacteria plate count is recorded in Table 15. Table 15. The total bacteria pepulation in samples plated and incubated according to Standard Methods Sample :Organi as per m1. Percent 59an ,9: milk smug , 291:9th , redngtigg Raw ; 8,300,000 Diverted : 50,000 Pasteurized f 22,000 Pasteuri zed: ; 20,000 Pasteurized ; 51,000 Pasteurized : 38,000 100.0 1.66 0.66 0.06 1.40 ..“OOOOOO”OOOON”””OOO 0.22 0.0 98.34 99.94 a z : 99.34 : 3 98.60 99. 78 The percentage rsduction of bacteria as tion averaged at least 99 percent (Table 15). b. Was: The determination of themoduric and themephilic organians was not made since the cream line a result of pasteuriza- reductions and the casein deposit on the paddle were still to be corrected. e. W The coliform organisms in the samples treated were as follows: Sample Desoxycholate plate count Raw 111,000 Diverted 10 Pasteurized 0 Pasteurized 1 Past eurized 0 Pasteuri zed 0 -54- F. PASL'EURIZATION 0F MILK SUSSTIT'U‘TING A SLIDING BOX FOR THE PADDLE IN ELECTRICAL GON'ILRQL In an effort to prevent the formation of casein in the heater, a sliding box was devised in such a manner that it would fit snugly into the heating chamber. The her out off the electricity by masking but did not affect the flow of the milk. The mechanical motion of the box was up and down, the up position providing complete masking of electrical input. The masking could be so complete that the current flow was barely perceptible, which was noticed by the ammeter needle slightly moving from the zero posi- tion. At first the sliding box was a block which was solid on the bot- tom except for four holes drilled through it. Later four flat pieces of insulating material were mounted in the form of a hollow box. 1.4mm The Operation of the pasteurizing equipment using the sliding box was identical as in the paddle control runs. The box was moved up and ~ down rather than in a pivot fashion as was the paddle. The voltage was changed from 205 to 245 volts. The run was shortened appreciably by the high voltage applied to the chamber, the same slight fluctuation of the meter needle which had preceded previous break downs was noticed. Approximately 15 minutes later this was followed by a drOpping of the milk temperature at the outlet call- ing for movement of the power input control to a higher position. This was quickly followed by a sulfurous off flavor in the pasteurized milk. 0n disassenbly it was found that a deposit of casein of about 1/8 inch maximum thickness had formed across the lower face of the shield block .0 v v u . e .. . ..ne-‘I- . ov - e I -55.. bridging the carbons and that this deposit, especially on contact with the carbons, had been blackened as by arcing. The box had possibilities of being used in the method of electri- cal control but further experiments were not carried out since the cost of the equipment and the necessarymodifications of recess foming would be far greater than the cost of the paddle previously used. The experience from the use of the sliding box pointed out that higher than 205 voltage should be avoided to keep down the amount of casein femation in the heater section. 9. PASTEURIZATION or MILK USING m moms TYPE course; AND A RESISTANCE STABILIZER Fem milk had a tendency to get warmer since warmer milk offered less resistance to the current flow. This caused a creeping of tapers-- tures while in forward flow to points beyond the nomal range. The com- psnsation for this creeping of tunperature was overcome by a constant change in paddle position which could not be done right at the moment of tempera- ture change. Therefore, a resistance stabilizer was designed to be acti- vated by the themostat setting to which it was attached. The electric wiring used in the pasteurizer with the resistance stabilizer is illus- trated in Figure 5. A record of the run is shown in Figure 6. 11.9mm After pasteurization was started, the manual control handle of the paddle was adjusted until the thermostat contacts were in action with nearly equal balance between the duration of opened and closed periods. This was done irrespective of the reading of the mercurial thermometer, the recording thermometer, or whether the milk was in forward or diverted flow. -66.. Fig. {i The system of electrical wiring used in the perfected pasteurb izer showing: 1. Main switch, 2. Electrodes, 3. Thermostat, 4. Stabilizing resistance, 5. Relay contacts, 6. Relay actuat- ing solenoid, 7. Pivotally supported primary power input control psddle. -- 57.. Figure 6. A record of a run made using the resistance stabi- li zer and the paddle for tmnperature control. Since the raw tank tenperature was too low for the hsater to heat the milk so that it would go into forward flow in a single pass, it was necessary to warm up the raw milk in the surge tank by diversion. The opera— ticn consisted of manipulating the manual control to position 10 so that the maximum penissible current was dram. This position was kept until the diversien valve was in forward flow. It was found that the power input cen- tral had to be well tended to prevent excessive current input during warm up. When the control paddle was correctly adjusted, the taperature at the re- corder and the behavior of the flow diversion valve took care of thanselves automatically. After the theme'stat signal clicked on and off intemittently for a few minutes, and the recording and mercurial themcmeters did not come up to pasteurizing tesperature, the adjustment of the thermostat was made so that a slightly higher taperature was required to open the contacts. This adjustment was quite sensitive and therefore, only a slight movement of the adjusting screw was made. .63. During the operation rawwnilk was added one can at a time. This prevented any radical changes in.temperature which.would cause the flow to go into diversion. When the change in temperature was anticipated the manual control handle was adjusted to consume:more current so when the milk was added the taperature would drcp to the normal pasteurization tenpera- ture. It was particularly desirable that no sudden drOp in rawwmilk tempera- ture beyond the range fer which the stabilizer would readily make compensar tion to prevent temporary diversion from forward flow. If'it was known that the next milk to be added to the raw tank was colder than the milk in the tank, the manual power input control handle was adjusted to increase the power input until the ratio of open to closed time of the ternostat contacts was approximately 5:1. ‘Upcn addition of the colderwnilk the ratio of open to closed thee automatically became less and the operator had an opportunity to stabilize the electrical input at the normal ratie of 1:1 if the temperature of the raw milk was not too drastic- ally'lowered. Conversely, if the milk that was added was warmer than that al- ready in the tank the manual control handle was first adjusted so that the ratio of closed to open duration was approximately 5:1. After the warmer ndlk was added the 5:1 ratio drapped, thus giving the opportunity to sta- bilize it at a 1:1 ratio by'nanipulating the power control if necessary. Except when adding raw milk it was found best to operate with a ratio of closed to open duration of the thermostat contacts of 2:1 or 3:1. This caused a saving of slight, unnecessary loss of electrical energy in the resistance stabilizer since the excess electrical energy was used to heat the resistance in the stabilizer. Data obtained from a run made by the Operating instructions just given are presented in Table 16. Table 16. A typical run using a paddle as the electrical control with a resistance stabilizer . : Tank = ' : : =Mercurial =Recording : Flow ’ Time 3 tmp.‘ =Control Welte‘themometefithemometer: direc- : °JW3Wflmijppufi 1° 1'.) i L0 L) #% tion 0 : 52 : 50.0 : 8.0 : 200 : 0.0 : 0.0 : D. 5 g 63 : 48.5 ; 6.5 : 200 : 159.0 ; 150.0 g D. 10 : 74_ : 38.0 ; 4.0 i 200 : 163.0 ; 163.0 ; F. 15 : 58* 49.0 7.5 200 : 162.0 152.0 r. 20 ; 58 ; 49.0 ; 8.0 ; 200 2 162.0 : 162.0 ; F. 25 g 56 :Adjusting :Adjusting: 200 g 164.5 ; 164.5 : F. 30 ; 70 : 44.0 f 6.5 i 200 ; 163.0 : 163.5 ; I". 35 : 50* :Adjusting gAdjusting: aoo : 157.0 : 157.0 : D. 40 ; 62 ; 49.0 ; 8.0 : 200 : 163.5 ; 164.0 ; 1". 65 : '70 i 49.0 : 4.75 i 198 : 162.0 : 162.0 : F. 50 : 'IO ; 50.0 ; 4.5 : 198 : 164.0 : 165.0 : F. 1“Raw milk was added. As is illustrated in Table 16, the telnperature remained much more constant throughout the entire run. The run was made to determine the effect of adding frequently small amounts of cold raw milk to lower the taperature cf the milk in the surge tank. Compensation for the lowering in surge tank tauperature was made according to directions outlined in the operation of the machine reported earlier. DISCUSSION The time needed to preheat the raw mill: in the surge tank, using the original equipment, was studied and was found to be too long for prac- tical operations. A higher voltage of 245 was substituted for the 208 volts previously used. This new voltage reduced the preheating time to as little as 5 minutes. This resulted in a great saving of time. The metering valve was used to raise or lower the temperature of the milk. This was found to be inadequate for when the flow was increased, the holding time decreased, while the holding time increased when the flow was decreased. This caused an overholding of the milk since the maximum flow resulted in 16 seconds holding while the minimum flow resulted in 33 seconds holding. This was corrected by changing the method of temperature control and by substituting a positive pump to provide a constant flow of milk. Thus the holding time renained constant throughout the runs. The head pressure of the pump caused a change in holding time even when the flow remained the same. When a check was made of the holding time while the valve position was set at 9, with the water level in the tank high and with it low, it was found that the holding time was 2 seconds greater at the lower level. lI'his meant that the milk would rennin in the holding tube two seconds longer than necessary. Thus, the lower water level might have been the cause of overholding. A home-made sol-u-bridge was found to increase the holding times in the same valve positions when compared with a commercial sol-u-bridge. The heme-made sol-u-bridge was found to be satisfactory but was slower in re- cording the closing of the circuits by the salt. The inaccuracy of the home- made sol-u-bridge could have been the cause of overholding. The gallons processed per minute depends upon the speed of the milk pump. The speed of the original pump was found to be 1600 revolutions per minute. This speed is such that much churning and agitation result dur- ing pumping and if cold milk is pumped the cream portion of the milk might churn into butter granules. To correct this a variable speed pmnp was found satisfactory to some extent at 1520 revolutions per minute. Lower speeds than 1520 caused a rapid rise in temperature and, therefore, poor con- trolling of the milk temperature. The agitator revolving at 60 revolutions per minute, caused no churning. The quantity of milk that flowed while in diversion was from 580 to 4,260 milliliters more than when the milk was in forward flow. This was found to be the cause of the rapid temperature rise when the milk suddenly went from diversion to forward flow. A restriction on the st- of the di- version valve was renoved to equalize the respective flows. Thus the tu- pcrature remained constant instead of rising rapidly when the milk went into forward flow. The turperature change was not responded to rapidly enough to make necessary adjustment in valve control. After 10 minutes of Operation in forward flow the milk would suddenly go into diversion for no apparent reason. Therefore, equipment was necessary that would respond rapidly to a slight change in tenperatures. This was found in the way of an emmeter, a paddle or sliding box, and a resistance stebilirer which will be discussed later. The crooning ability of the milk treated with the original equip— ment was found to be reduced by as much as 50 percent. The reduction was found to be due to churning action of the centrifugal pump Operating at 1600 rounds per minute. Installing a Waukesha positive pump overcame this difficulty and this will be discussed in a later paragraph. The physical, chuical and bacteriological tests were found to be satisfactory except the crooning ability of the milk. Cooked flavor re- sulted if treatment tenperatures exceeded 165° 1‘. The acidity of the milk dropped by as much as 0.01 percent as a result of pasteurization. Bacterial reduction was as much as 99.9 percent. Since there were definite signs of overholding, this was not considered significant. The pup was found to be inadequate for it also chnrned out por- tions of the cram. The extent of cream line reduction caused by the vari- able speed pmnp was 46 percent. The pump was therefore discarded. ii? .1 v .4. .._ ,‘" u -. .: ‘,.'.. : Way-3:1 on: 8 um- =10. 4:: Ot-v- I‘ith the substitution of the positive pmp it was necessary to re- move the themal themcneter, the variable speed pump and the metering valve. With their rucval the Waukesha positive pump replaced the variable speed pump; a 212° 1‘. indicating thermometer replaced the metering valve, and a petcock was placed in the thermal themometer. Iith the new equipaent installed, the milk processed per hour was found to be 357 pounds. The amount of milk could be increased or decreased by increasing or decreasing the length or width of the holding and adjust- ing the speed of the pump to couponsate the holding section increase. The adjustment should be made to such an extent that the holding time was 16 seconds. ;._9 at es 0 g _;’_ag 6:3;u_;n :e e’fuete -' ta ta; 08.10; B 5 Since the metering valve was discarded, the method of Operation was changed. An indicating (mercury-in-glass) themometer was placed at right angles to the holding section in the place of the metering valve, thus providing the much needed indications of temperature changes taking place in the heater. The type of run was found to be favorable since the milk mained in forward flow for a much longer period of time, since ad- Justnents in controls could be made Just about as fast as the changes were taking place. Upon dissanbling the heater section and moving the paddle it was found that a heavy ceseous deposit formed on the edge of the paddle. The deposit shorted the electrical circuit and thus caused the meter to weave during the run. The conclusion was not reached, however, until the paddle section was dissembled. The creaming ability of this milk was affected much less than was ever encountered before. Therefore, the paddle method of electrical control was considered to be the best tried. The extent of cream line reduction was only 16.6 percent. Sixteen and six tenths percent reduction was considered to be too high and an effort was made to reduce the loss. It was thought that there was arcing of electricity in the chamber and thus a "hot spot“ -74- develOped which precipitated casein and therefore, also injured the crem— ing ability of the milk. The bacteriological tests conducted on this run were found to be satisfactory since a reduction of as much as 99.§4 percent was encountered. No count was greater than 51,000 organisms per milliliter. The colifom counts made by using desoxycholate were found to be 0 in all pasteurized saxnples but one. The raw milk of this test contained 111,000 organims per nilliliter. The phosphatase tests of all pasteurized samples in this and all prior runs were negative, while all raw and diverted samples were positive. 4A-! _-t .. f u Wm). In an effort to prevent casein deposit formation, which was found :10: _ q__.0 a ; e so 00‘ e t:.* 0a‘_[ . lg -_ __ . .... to be the cause of a foul, sulfurous flavor in pasteurized nilk, especially after a four or five hour run, a sliding box was substituted in the heating chamber. The effect the box had on the electricity passing through the milk was the same as if the length of the electrodes was shortened by cutting. As the box loved up it covered a greater area of electrode, thus reducing the electrical effect of the milk. Therefore, the tauperature of the milk was reduced. The be: also caused the off-flavor to develop in the pasteur- ized milk. However, it was found that voltages greater than 805 enhanced the developent of the casein deposit. Plans are in the naking to design a paddle which not only would pivot but would also slide up and down in the electric heater. This would give the features of both the sliding box and the paddle. It was also learned that cooling water on the electrodes re- duced the tendency of casein deposit. Won. 9:, ”WW stabilizer The stabilizer was wired into the circuit as is shown in Figure 6. It acted to the setting of a thermostat: which was substituted in the place of the indicating thermometer. The set screw of the thermostat was adjusted so that its range would be between 164 and 165° 1". Therefore, any temperature above 165° I. could not be taken care of by the 1/2 ohm resist- ance in the resistance stabilizer box. The milk leaving the heater was between 164 and 165° 1'. When these tenperatures were approached, the signal (a mall volt meter) responded intermittently, thereby taking care of the tendency of warm milk to rise in temperature due to its lesser conductivity at higher tunperatures. With the thermostat setting at 164 to 165° F. the milk traveled through the holding tube where the tuperature drapped as much as 8° 1'. The recording and mercurial thenometers regi stared temperatures of 161° 1". Several precautions must be observed when using the stabilizer as an automatic method of temperature control with the pivoting paddle. The problems of stabilization of the intermittent, on-and-off signal encoun- tered when adding cold or excessively warn milk to the surge tank can be overcana if a large insulated storage tank is used. The operator would be required to stabilize the raw storage tank temperature with the control paddle in the heater and the intermittent signaling only once during the pasteurization of the entire storage tank of milk. With the stabilizer added to the paddle manual control, it was found that a sensitive control could be had and that the milk would stay in forward flow for a long period of tine. The producer-size Electra-pure pasteurizer was found to be eco- nomical in operation since only a source of electricity is the added re- quirement; while if holding processing was practiced on the farm, soft water for the boilers and a source of fuel would be required. W The Electra-pure machine is designed to consume 10 kilowatts per hour. Therefore, 10 kilowatts would pasteurize 357 pounds of 35.7 pounds would require one kilowatt. The cost of a kilowatt in the rural areas is .02 cents. So i531 equals 17.85 pounds pasteurized for one cent. 3:99— equals approximately nine quarts of milk pasteurized for one cent. This equals 0.11]. cents per quart of milk as the cost of pasteurization. ; 3". ; :‘I . ..1 ' . ‘8; ‘1', _:t . . ’93: 004i” I c: L O l tle ..‘O ; y 'L: g ; g 1‘- The milk for the comparison was obtained as described in the ex- perilental procedure. The milk was then pasteurized in the experimental pasteurizer and saxnples were taken for chemical, physical and bacteriologi- cal analysis. The only advantage held by the holder method of pasteuriza- tion was the lower amount of crooning ability that was lost. Other than this there was no apparent difference in bacterial destruction except that colifom organise were found more often in the (vet) holder pasteurized saxnples than in the high-tunperature short-time pasteurized samples. The milk was not checked for thamoduric or themephilic organims in the cmparison of pasteurization processes since it is known that theme- duric organims survive high-tanperature short-time pasteurization much easier than in holder pasteurization. If the test were conducted with a special link, such as high thermoduric milk, than it would be a particular -77- special milk which would not be the case commercially. If a high theme- duric count in raw milk is tolerated, then regardless of the method of pasteurization, high total counts will result. Due to the fact that a local dairy recently installed a steam type high-tunperature short-time pasteurizer, it was thought that a comparison of efficiencies of pasteurization might be carried out. The results of the tests indicated that there were only a 7- pereent loss of crooning ability in the case of the comercial unit, while the experimental model reduced the creaming ability by as much as 24 percent. The phosphatase tests were all negative in the pasteurized samples. The coliform tests were negative in all the mercial pasteurized samples while the experimental souples showed one positive colifom test and that being only one organism per milliliter. The desoxycholate agar was used for plating the colifom organisms which appeared as red colonices be- tween the two layers of media. This media was found excellent and is used as routine testing in the Michigan State College Dairy Bacteriology Lab- oratory. In all comparisons of the different methods of pasteurization, only one sample obtained from the experimental model had a total bacterial count of 50,000 organimns per milliliter. It was not considered serious since the count was 51,000 organians per milliliter. It must not be overlooked that at least 40 complete runs were made in the experimental pasteurizer, three runs with the holder pasteurizer and only one with the commercial unit. Therefore, the possibility of obtaining colifom organisms in the experimental pasteurizer was much greater. W With respect to original equipment when 240 volts was used with a 6-inch heater the time required to heat the milk to pasteurization tem- perature was only 15 minutes; whereas 90 minutes were required when 205 volts was used. The metering valve was ineffective as a means of temperature con- trol. Any necessary changes to compensate for rise in temperature affected the holding thme which fluctuated between 16-33 seconds. lethods of time-temperature control included a metering valve, thermal thermometer and centrifugal pumps. All were found to be inadequate. When.milk went from diverted to forward flow'the volume decreased as much as 29.5 to 125 percent, causing a marked, rapid rise and a lack of control in the temperature of the processed.milk. Although pasteurization so far as reduction of organisms and elimination.of colifo:m.bacteria were concerned was adequate, the creaming ability of the milk was reduced by as much as 50 percent, a cooked flavor was encountered and some churning resulted. With respect to redesigned equipment, the original attempted time-temperature controls were replaced by a positive'Waukesha pump and an indicating thermometer which provided satisfactory operation but required constant attention. Later a manual control paddle (Figure 8), a sliding box (Figure 9) and a resistance stabilizer were added to affect a.more sensitive control. These were found very effective. However, some minor adjustments were feund necessary to prevent off-flavor develOpment and deposition of casein on parts of the heating unit. The redesigned equipnent yielded adequately pasteurized milk with a high percentage of bacteria reduction, having excellent flavor and no cream plug, but impaired the creaming ability by as much as 21 percent. N »\ O "M'. .-‘mo ..m1'0' . 5&ch e. 5.533.355 e woeaesuuumgou voice 55 ooeeabm 34. .854... canon s 33:25.. 333583. 23 due pugwsgum usage. -08- fiat. Be Showing two views of the herd rubber electrical control paddle Just as it was removed from the upper end of the heater. The white spongy material is casein deposit. —— Figure 9. Sliding box, electrical control, showing: 1. Adjusting handle 2. Preheat sample point :5. Porcelain insulation 4. sliding box. Resinous (1) (8) (a) (e) (5) (6) (7) (8) (9) (10) (11) -83- LITERA'IUBB CITED Anderson, A. I. and rinkelstein, R. 1919 A study of the neetro-pure process of treating nilk. J’our. Dairy Sci. 22374-406. Anonymous. 1938 Chronology of pasteurization developents. Assoc. Quart. 1:32-33. Ayers, 3. B. and Johnson, I. 1'. 1’24 The ”majority” and "absolute“ thenal death points of bacteria in relation to pasteurization. Jour. Beet. 98279-284. Ball, 0. 0. 194.5 Short-tine pasteurization of nilk. , Ind. and lag. Chas. 35:71. B..t‘1.. J. n. 1916 Electrical treatment of still: for infant feeding. Jour. of State led. (London). sun-113. Beattie, J. l. and Lewis, I. G. 1925 On the destruction of bacteria in nilk by electricity. Jour. Hygiene 24:123-137. Beams, 3. A. 1930 The Escherichia-aerobacter group as an index to proper pasteurization. Jour. Dairy Sci. 13:94—101. ‘Bell, R. I. 1925 The effect of heat on the solubility of calcium and phos- phorus compounds in silk. Jour. Biol. 0b.. 64:391-400. Bell, 3. I. and Sanders, C. I. 19“ Prevention of nilk stone fonation in e high-taperature short-tine heater by preheating nilk, ski-nilk and whey. Jour. Dairy Sci. 29:499-504. Brannon, J. I. and Prucha, M. J'. 1924 The effects of pasteurization taperature on individual gems found in nilk. J'eur. Dairy Sci. 10:263-268. Breed, R. 8. 1928 Thermophilic bacteria in nilk pasteurized by the holder pm“... Io Ye ASI'. mte Stan (Mm) TMe Bill. 1910 (12) (13) (14) (15) (16) (17) (18) (19) (20) (32) -a4- Breed, R. S. and Prickett, P. 8. 1929 The significance of thermophilic, spore-foning bacteria in pasteurized nilk. J’our. Bact. 17:37. BECK, Te 0. 1962 False positive phosphatase test from a thenophile in pasteurized nilk. her. Jour. Pub. Health 323224-1236. “tun, 1. Co 1940 fight-perature short-tine pasteurization. Jour. [ilk Techne1. 5:198-203. mat”, a. I. 1929 The effect of heat produced by an alternating current on tubercle bacilli in nilk. Jour. Bast. 17(1):38. Gavanaugh, I. W. 1946 Problus in the operation of high-t-perature short-tine pasteurization: cleaning, sterilizing, maintenance and tiling of operations. “Che are hpte Sta-e SD06. Me 355. ”e lklge Gohn, n. 1946 lxperience in checking high-tuxpemture short-tine pasteurization te neet public health requiruents. lick. me hpte Stae S’.°e Me 535. We ”'27e Ours-en, E. R. endlvans, I. R. 1945 Heat activation inducing genination in spores of theme- tolerant and themophilic aerobic bacteria. J'our. Bact. ”(4)535. Dahlberg, A. c. 1932 The nargin of safety between the thenal death point of the Tubercle Bacillus and the themal cream layer volume impairment in pasteurizing nilk at various tunperatures. New York (Geneva) Agr. ill-pt. Sta. Bul. 203. “here, A. 00 1946 The keeping quality of pasteurized nilk. Ne Ye (00111.11) Acre lxpt. Stan 3'31. 858. 23 pp. Dahlberg, A. 0., Holland, R. 1., and liner, R. X. 194.1 "Quick-tine” asteurization of milk. Ne Ye (MOW me kpt. Stae TOOhe Me gale MOmuI, I. DO 1929 nectro-pure process reduces bacteria in nilk. lich. Agr. Expt. Sta. Quart. Bul. 12 (1):20-22. (25) (24) (85) (28) (27) (28) (29) (30) (31) (as) (33) (34) -35... Dean, I. J’. 1927 Pasteurizing by electricity. Pa. Agr. Expt. Sta. mfl1.th Ann. Rpte Bill. 215. Dotterer, 3. D. 1939 High-taperature short-tine pasteurization. Jour. Milk Technol. 2:197-198. Dotterer, W. D. 1943 Heat resistant organisms in nilk supplies. Jour. Milk Technol. 6 (5):269. Dowd, 1.. R. and Anderson, I. 0. 1943 Study of short-tine high-tesperature pasteurization of ice cream nix. J'our. Dairy Sci. 26:37-46. nvehjn, O. A. 1941 No objections to pasteurized milk on nutritional basis. n11]: Plant Monthly 30(7):26-29. Irwin, R. 1945 High-tuperature short-tine pasteurization. Milk Plant lonthly 34: Iabian, I. W. 1942 Themeduric organises in relation to high-taperature short-tine pasteurization. Iour. Milk Technol. :237-242. M, Ae O. 1927 Theme-tolerant organius as a cause of so-ealled pin-point colonies. .Tour. Bact. 13: 347-377. Elbert, '0 II. 1945 Bigh-tuperature short-tine pasteurization. lilk Dealer 34( 7) : 76-80. Pinkelstein, R. 1919 The occurrence of the Colon-derogenes group of organics in raw and pasteurized nilk and its significance. Jour. Dairy Sci. 2:460-481. ”1", o. P. 1934 Few type of nilk plant features two systems of pasteuriza- tion. Iilk Dealer 26:40-42. Gelpi, A. J’. 1931 Studies on the nectro-pure process of nilk "purification." Thesis for the degree of It. 3., lich. State college, E. Lansing. (35) (36) (37) (as) ('59) (40) (41) (42) {43) (44) (45) (46) -35- Getchel, B. n. 19 35 Electric pasteurization of nilk. Ag. Eng. 16:408-410. Gilcreas, I. W. and Davis, W. R. 1926 An investigation of the amylase and phosphorus tests as an indication of pasteurization. Twenty-fifth Ann. Rpt. Assoc. nilk Sanitarians. 15-32. Gillespie, D. 1944 Steam high-teaporature short-tine pasteurization. lilk Plant lonthly. 26:36-65. Gould, I. A. 1946 Sons clinical changes produced in nilk by high-teaperature heat treatment. Milk Plant lonthly 33(9):70-'fl.. Gould, I. A. and Summer, H. H. 1939 Effect of heat on nilk, with special reference to the cooked flavor. lich. Agr. hpt. Sta. Tech. Sol. 164. m1, :0 A. 1945 imperature controlling high-taperature short-tine pasteurization process. Jour. Dairy Res. 14(1-2):1-20. Bauer, B. I. 1916 Studies on the creaning ability of nilk. IQ“ Agre hte Sta. ROS. We 51. Humor, B. W. and front, G. l. 1929 A study of yellow cocci which survive pasteurization. Jour. Dairy Sci. 11:18-23. , 'E. A. 1921 The effect of temperature of pasteurization on the creasing ability 0: fine 111. Age Into Stae 3111. gave Harding, 3. A. . 1930 Observations on effects of themophilic bacteria in pasteurized nilk. Intern. Assoc. Dairy and [ilk Insp. NHOtMth Anne Rpte 135‘1‘3e £11.“. J. Le. MOI" no ma Sp“, I. L. 1941 I. Themaduric bacteria in pasteurized nilk. II. Studies on the bacteria surviving pasteurization with special reference to high-taperature short-tine pasteur- ization. Jour. Dairy Sci. 24: 303-315. Hiluan, J'. 1.. 1940 Themcdnrie bacteria in pasteurized nilk. A review of literature. Jour. Dairy Sci. 23:1143-1160. (47) (as) (49) (50) (51) (68) (53) (54) (55) (56) (5') -37- mamx. E. B. 1943 High-taperature short-tine pasteurization. Proc. Soc. of Agr. Bact., Hat'l Inst. Bee. in Dairying, Univ. Beading, England. Hiscox, l. R. and Davis, J. G. 1943 Pasteurization, holder and high-taperature short-tine. Milk Industries 23(11):29. mland, R. F. and Dahlberg, A. C. 1940 The effect of the time and taperature of pasteurization upon ease of the properties and constituents of nilk. Re Yo (M073) Agl’. Expte Stae TOChe Bill. 25‘. Belles, A. D., Lindquist, E. 0., Jones, 0. P. and Anne W. Wertz. 1943 Effect of high-t-pemture short-time pasteurization on the ascorbic acid, riboflavin and thianin content of milk. 3011!. MI", 831. 28‘ 29-33e lblnes, A. D., Jones, 0. P., Anne I. Hertz, and Iumeski, 3. I. 1943 lffect of holder pasteurization on the ascorbic acid, ribo- flavin, and thiamin content of 1111:. Jour. Hutr. 26(4); 337-343. Bolnqui st, 0. A. 1932 High-taperature short-tine pasteurization. Twentieth Ann. Rpt. Intern. Assoc. Dairy and Milk Insp. p. 79. bit, 1.. I. 1943 Checking camercial high-teaporature short-tine pasteur- ization installations. Jour. Hilk Technol. 2:198-199. Hacker, 0. J. 1928 A study of the cocci resisting pasteurization tuperatures. I. Y. (Geneva) Agr. lxpt. Sta. Bul. 134. Jensen, J. l. and Bortree, A. L. 1946 Storage and treanaent cf milking machine inflaticns. Jour. Dairy Sci. sameness-859. Kay, 3. D. and Graham, W. R. 1933 Phosphorous compounds of nilk. VI. The effect of heat on the silk phosphatase. Jour. Dairy Res. 3-63-63. Iilbourne, 0. H. 1922 The relation of tuperature to cross layer in pasteurized nilk. 1Eleventh Ann. Rpt. Intern. Assoc. Dairy and lilk Insp. (58) (59) (60) (61) (62) ( 53) (64) (so) (66) (6'7) (as) -33- Levowitz, D. 1943 The origin and control of thcmoduric organises. Some hmdmantal phases. N. Y. State Assoc. Iilk Sanit. Ann. Rpt. 19:219. lacOurdy, R. D. and Trout, G. I. 1940 The effect of holder and flash pasteurization on some flavors. The effect on corn and alfalfa flavors. 3011:. 136117 801. 23:855-860e legcc, H. ’3. and Harvey, D. 1926 Some plusico-cheaical changes induced in milk by heat. Biochaa. Jour. ”:873-874. Iallnann, I. 1., Bryan, 0. S. and Fox, I. K. 1940 A new nicroscopic procedure for the detecting and locating of the source of thermoduric organism in nilk. fourteenth Ann. Rpt. N. Y. State Assoc. Dairy and Iilk Insp. pp. 167-173. larquardt, 3'. 0. and Dahlberg, A. O. 1931 The creasing of nilk pasteurized at high taperatures. H. I. (Geneva) Agr. hpt. Sta. Bul. 180. larquardt, J. C. and Dahlberg, A. C. . 1934 Pasteurized nilk flavor and creasing power as affected by heating medium tesperatures and pasteurizer linings. No to (3.30") Agr. 11th 3‘91. Me 883. ntm. I. 1929 The effect of heating on the constituents of nilk. Osaka Jeur. led., 28:333-362. hearsay, ll. 3. and Langevin, I. 1932 The eoli-aeragencs detcnination in pasteurization control. Jour. Dairy Sci. 13:321-329. lillenky, 'A. and Brueckncr, E. J. 1941 A comparative study of high-tupcrature short-tine, and holder pasteurization. No to (mum) ‘81.. Int. 8‘93. Bill. Me Iocre, 0. H. 1943 Cleaning and sterilizing short-tine high-tupcraturc pasteurizers. lilk Plant lonthly 34(1):62-63. Iorril, as 8e 1943 The detection and source of themeduric organics in raw nilk and their effect on the resazurin test. Proc. Soc. Agr. Brit. ”-30. (69) (70) ('71) ( 72) ( 73) ( 74) (75) (76) (V7) (76) ('79) (80) -89- nudge, 0. S. 1930 A life cycle of a themophilic organism. Pros. Soc. Expt. Biol. [ed. 28(11):202-203. more, R. P. and Pence, J. A. 1941 A‘ simplified procedure for the laboratory examination of raw milk supplies. Jour. [ilk Technol. 4:16-23. North, 0. B. and Park, W. H. 1927 Standards for milk pasteurization. Am. Jour. of ageine 7:147. O'Daniel, V. F. 1942 The problem of thcnoduric bacteria in short-tine high tunpcrature pasteurization. Jour. Beet. 44(3):.387. 08d“. H. Ne, Carpenter, cc 1!. and W. H. Re 1924 A report of the studies made on the Elastic-pure process for the pasteurization of milk as carried on at the Dairy Department, Cornell Univ., 1924. Compilation of studies and tests on the nectro-pure process. p. 1-88. ([incographed). 018011, Re to 1946 Routine maintenance of short-time pasteurization control Bystana. "1011. 381‘. mt. Stae Spec. Bule 33536573. Overman, 0. R. 1943 [onthly variations in composition of milk. The 11111: Dealer 34(6):42-44. Palmer, A. [. 1944 The Trumbull Electra-pure pasteurizer. Jour. Milk Technol. 7: 283-286. Phillip.. Co A. 1928 The effect of flash pasteurization of milk upon the flavor and texture of cheddar cheese. Jour. Dairy Sci. 11:292-298. mm, 00 SO 1893 Dairy experiments. Indiana Agr. prt. Sta. Bul. 44-. Price, I. H. 1922 Report of the coxmittec on pasteurization. 11th Ann. Rpt. Intern. Assoc. Dairy and [ilk Inspectors. Putnam, s. A. 1943 Bigh-tapcrature short-time pasteurizing equipment from the operator' a point of view. [ilk Plant Monthly 34(1) :33-54. (81) (82) (83) (ea) (85) (36) (8") (88) (89) (90) (91) -90- Quinn, J. D. and Burgwald, 1.. H. 1933 High short holding and low long holding. [ilk Plant Honthly 28:2, Do we Bishoi, A. H. 1947 What to check and how to check on short-time pasteurizers. Reprint Cherry-Burrell Circle, Man-Apr. ’I pp. Robertson, A. H. 1927 Themophilic and themoduric micro-organism, with special reference to species isolated from milk. I. Review of literature. 1!. I. (Geneva); Agr. hpt. Sta. Tech. Bul. 130e 36 We Robertson, A. H. 1927a Thermophilic and thermoduric micro-organise with special reference to species isolated from milk. 111. Description of non-sporc-foming thermoduric organisms isolated. Ne Ye (00110?!) Agr. Expt. 8‘3. T.Che Bus Isle 62 pp. Robertson, A. 3., Yale, N. W. and Breed, R. S. . 1923 Nonthcrmcphilic, spore-forming bacteria associated with pasteurizing equipnent. N. I. (Geneva) Agr. hpt. Sta. Bul. 119. Robinson, 1'. I. ‘ 1923 Studies on the electropurification of milk. Rpt. by Robertson Laboratories, Inc., Detroit, [ich. pp. 1-32. Sandorf, I. J. 1938 Effects of high voltage on the bacterial count of milk. Univ. of Nevada, (Reno) Bul. 3. Sharp, P. E., Trout, G. I. and Guthrie, B. S. 1936 The relation of oxidized flavor to pasteurization tapere- turcs. 10th Ann. Rpt., N. Y. State Assoc. Dairy and Milk Insp. pp. 143-164. Sherman, J. [. and Wing, Helen U. 1933 The significance of colon bacteria in milk with special reference to standards. Jour. Dairy Sci. 16:163-173. Skclton, F. M. and Sommer, H. H. 1944 A study of cream rising in milk. Jour. Dairy Sci. 27:521-330. Samar, H. E. 1945 mmmm We. 2nd ed. 745 pp. EV [ilwaukce, Wis.: Olson Publishing Co. —.- ;--- (92) (93) ( 94) (95) (96) (97) (98) (99) (100) (101) (102) (10:5) -91- Spcck, Ii. 1.. 1947 The resistance of pigmeoccug WELL-9141 in laboratory high-temperature short-tine pasteurization of milk and ice cream mix. Jour. Dairy Sci. 30:975-981. Stark, C. N. and Patterson, M. 0. 1936 The heat resistance of colon organisms in milk. Abst. Jour. Dairy Sci. 19:493-496. Stone, G. E. 1909 Influence of electricity on microorganisms. Bot. Gaz. 68(3):339-379. Tanner, I. W. 194! W nim- 8nd 04- 1196 pp- viii WPrcss, Champaign, I11. Ticdanan, W. D. and Swanncr, R. 0. 1940 Bigh-tmpcrature short-tine pasteurization. Bul. R. Y. State Health Dept., Albany. 16 pp. Tracy, R. 1.. 1932' Lethal effect of alternating current on yeast cells. Jour. Beet. 24:423-438. Trout, G. M. 1946 Highlights of research on high-tmpcrature short-time pasteurization. [ich. Agr. Expt. Sta. Bul. 333. pp. 76-85. Wainess, E. 1941 BacteriolOgicel problms in high-tupcrature pasteurization. Amer. [ilk. Rev. 3: 282-284. Weber, 0. W, 1946 Safety factors of high-taperature short-time pasteurizers. 12th me Byte He Ye State “wee Mijk Sanitarium no 49" 50, 62.54, 56.58. ‘0'62. 6"“, ‘8'”, 78.”. Weizmann, I. 1893 [ethods of milk conservation, especially pasteurization and sterilization. Iiel Bxpt. Sta. (Cited in Assoc. Quart. Hay, 1938. [ilk Ind. round. Original not seen). leinreich, c. I. 1943 Pros and cons of hot short pasteurization. um: Plant [onthly 34(1) :cc-cs. Ieinreioh, G. 1'. 1943s Short-tine high-tuperature pasteurizers. The [ilk Dealer 34(3):92, 94, 96, 98. -92- (10.) 1.1., 11.1. 1933 High-temperature, short-time holding pasteurization in the United States. Intern. Assoc. of Hill: Dealers (Lab. Sec.) Proc. 26th Ann. 0011?. pp. 10-59. (105) Isle, I. I. and Kelly, C. D. 1933 Thermophilic bacteria in nilk pasteurized by the high- tuparature short-tine method. N. I. (001101791) Aer. El'pt. st§e Me ewe