SOME PROCESSING METHODS WHICH MAY AFFECT QUALITY IN ICE CREAM Thesis for the Degree of M. S. MICHIGAN STATE COLLEGE Roger HaroId WIIkowske 1950 This is to certify that the thesis entitled "Some Processing Methods which May Affect Quality in Ice Cream" presented by Roger Harold Wilkowske has been accepted towards fulfillment of the requirements for M.S. degree in Agriculture % Major professor [hm March 9, 1950 0-169 '37- .1». .‘ v‘ "u‘ifi—r “flvr v— PLACE IN RETURN BOX to remove this Checkout from your record. TO AVOID FINES return on or before date due. MAY BE RECALLED with earlier due date if requested. DATE DUE DATE DUE MEIR2171“2%06 6’01 c:/CIRC/DateDue.p65-p.34 SOME PROCESSING METHODS WHICH MAY AFFECT QUALITY IN ICE CREAM SOME PROCESSING METHODS WHICH MAI'AFFECT QUALITY IN ICE CREAM 35' ROGER HAROLD WILKOWSKE w A THESIS Submitted to the School of Graduate Studies of Michigan State College of.Agriculture and.Applied Science in.pertiel fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Dairy 1950 ACKNOWLEDGEXEKTS The writer wishes to eXpress his sincere appreciation to the following: Professor P. S. Lucas, Associate Professor of Dairy Manufacturers, under Whose direction this investigation was done, for his helpful planning and guidance in carrying out this work and in preparing this manuscript; Dr. Earl Weaver, Head of the Department of Dairying for placing the facilities of the department at the writer's disposal; Dr. Joseph A. Meiser, Jr., Assistant Professor of Dairy Manufacturers, for his kind assistance in the preparation of this manuscript. 232993-53 INTRODUCTIOI . . . . . . REVIEW OF LITERATURE .~. Pasteurization . . Homogenization . . Protein stability . Aging....... Freezing . . . . . Hardening ice cream Ice crystal size . PLAN'OF EXPERIMENT . . PROCEDURE AND.RESULTS . l. The Effect of Varying the Pasteurization Temperature TABLE OF CONTENTS 0 the Quality of the Ice Cream ProcedureOOOOOOOOOOOO00000.90 O O O O O O O O I O O O O 0 Ingredients . . . . . . . . . . . . . . . . Preparation of the mix Tests for qpmlity . . . Experimental Results . . . . ‘Discussion of Results 2. The Effect of varying the Homogenization Pressure on the Quality of Ice Cream Procedure Experimental Results . Discussion of Results 0 O 0 o 0 o O 10 11 13 15 16 17 19 19 19 19 20 21 25 39 1+2 M2 58 Page 3. The Effect of varying the Homogenization Temperature on the Quality of Ice Cream. . . . . . . . . . . . . . . . . . 61 Procedure . . . . . . . . . . . . . . . . . . . . . . 61 Experimental Results . . . . . . . . . . . . . . . . . 62 Discussion of Results . . . . . . . . . . . . . . . . 77 M. The Effect of Varying the Aging Period on the Quality of Ice Cream.. . . . . . . . . . . . . . . . . . . . . . . . . 79 Procedure . . . . . . . . . . . . . . . . . . . . . . 79 Experimental Results . . . . . . . . . . . . . . . . . 80 Discussion of Results . . . . . . . . . . . . . . . . 96 5. The Effect of varying the Hardening Temperature on the Quality of Batch and Continuously Frozen Ice Cream . . . . 99 Procedure . . . . . . . . . . . . . . . . . . . . . . 99 Experimental Results . . . . . . . . . . . . . . . . .100 Discussion of Results . . . . . . . . . . . . . . . . 11? SUMMARY AND CORCLUSIOES . . . . . . . . . . . . . . . . . . . . 120 LITERATURECITED0000.09000000000000.000123 I II T RODUC T I ON This investigation was initiated as a part of a larger study of quality in ice cream. Since quality is dependent upon the mix ingre- dients, processing, and subsequent handling of the frozen product, the factors investigated were some of those about which questions are frequently asked. This field is so broad that it was necessary to limit the scope of the investigation to the effect of processing methods. The plant operator finds it difficult to measure accurately changes brought about by simple variations in processing. Hany such changes may be ascertained only by the use of chemical apparatus or bacteriological methods. Similarly, defects in ice cream may be attributed incorrectly to Specific procedures and changes made which are not detrimental to quality. Changes in pasteurization, homogenization, aging, freezing, and hardening may or may not effect slightly or pro- foundly the type of ice cream, but it is vital that the plant processor know the trend of this effect. Consequently, the factors considered in this thesis have been those which are encountered in all ice cream plants. They are those commonplace factors which may be varied by accident or carelessness, may be changed to avoid a defect, or may be adjusted merely to improve the resulting product. A vast amount of research has been devoted to the effect of pro— cessing methods on the quality of the ice cream. finch of this work has been assembled and cited in the review of literature; however, the results of these previous studies in some cases are not applicable to this study due to the differences in present mix composition, processing equipment, and testing methods. REVIEW OF LITERATURE The problem of quality has long been one of moment to men in the field of dairying. In the ice cream industry, there has been a great deal of investigation.and research on quality. In this thesis an ef- fort has been made to record as much of this information as is available and pertinent to the problem of the effect of processing methods on quality. Pasteurization. Gregory and manhart (4S) concluded that methods of preparation and treatment of ice cream mixes affect both the physical and chemical properties of the mix. They reported that pasteurization reduces the viscosity of the mix, which results in lesser overrun ob- tainable unless the viscosity is restored. The advantages of pasteuri- zation, as listed by Martin (66), are that pasteurization improves keeping qualities, destroys harmful bacteria, aids in dissolving mix ingredients, and reduces the bacteria count. martin, Swope, and Knapp (69) found that increasing the pasteuri- zation temperature from 145°F. to léSoF. has no appreciable effect on the acidity, pH, overrun obtained, or time required for freezing. They noted that the higher the pasteurization temperature the more efficient was the destruction of bacteria. Dahle, Keith, and McCullough (21) noted that higher pasteurization temperatures produces the desired overrun in somewhat shorter time. Dahle and Earnhart (20) found that pasteurizing the mix at 170°F. to 180°F. increases protein stability but decreases fat clumping, viscosity, and freezing time. They concluded that higher pasteurization temperatures have a greater effect on the viscosity, overrun 3 and protein stability than do higher homogenization temperatures. Sommer (90) stated that dairy products heated to 170°F. or higher develop a slight cooked flavor, but that they are less likely to develop an oxidized flavor. 'Wbrking on prolonged holding at pasteurization temperature, martin (65) observed that holding at lSOoF. for 3.5 hours resulted in a slight decrease in viscosity and an increase in protein stability. He reported that the holding did not impair the whipping properties or quality. There have been other methods of pasteurization suggested. Dahle and Knutsen (22) reported that the Electropure process of pasteurization is more efficient than the holding method in destroying bacteria. Dowd and Anderson (29), working with a high—temperature—short-time unit, concluded that ice cream mix, made from cream, milk, and skim milk flakes, can be successfully pasteurized. They added that lBOOF. for 19 seconds is as effective as 160°F. for 30 minutes. Fabricius (38) reported that vacreated ice cream mix in comparison to vat pasteurized mix is superior in flavor score by 1.29 points and that vacreation delays the development of stale, oxidized, and metallic flavor in the finished ice cream. Very favorable results from the use of the Vacreator in making ice cream mixesvmne reported by Wilster (98}. Wilster and 1m (99) reported similar results and concluded that vacreation efficiently reduces bacteria, causes no protein destabilization, and produces a fine flavored mix. There has been considerable work done on the effectiveness of pasteurization in reducing bacterial population. Fabian and Cromley (37) first reported that pasteurization resulted in a 94.5 to 99.9 per cent reduction in the bacterial count of the mix. They noted that any subsequent operation has a general tendency to increase the plate count. It was observed by Fay and Olson (43), Olson and Fay(77), and Brannon (9) that extreme pasteurization temperatures are unnecessary in producing ice cream of low bacterial content. Fabian and Coulter (36), Paley and Isaacs (78), and Speck (93) agree that ice cream mix exerts a protective action for bacteria at the pasteurization temperatures. Dubois and martin (30) reported that in mixes made from pasteurized dairy products, the flora consists largely of slow acid formers. Various investigators — Hahn and Tracy (48), Burgwald and Gib- erson (10), Caulfield and martin (ll), Hahn and Tracy (48), and Nelson, Caulfield, and Martin (76) - have investigated the applicability of the phosphatase test to ice cream. They agree that the test can successfully be used on ice cream mix and that a pasteurization temperature of lSOoF. for 30 minutes will give a negative test. Martin, Nelson, and Caulfield (68) noted that although there was a certain relationship between various tests, the difference was enough to necessitate a variety of tests to ascertain the true quality of ice cream. After examination of thermal death point of pathogens, work on the coliform group, and results of the phosphatase test, Armstrong (5) concluded that lSOOF. for 30 minutes is a satisfactory minimum requirement for pasteurization. Sommer (90) supported the conclusion stating that for ice cream mix, made from reasonably good ingredients, a pasteurization temperature of_lSO°F. for 30 minutes is adequate. Homogenization. Homogenization has become an indispensable process in the preparation of an ice cream mix and is necessary to prepare quality 5 ice cream with modern freezers. The process of homogenization brought additional problems. Reid and Moseley (84) stated that processing the mix increased the viscosity by increasing the surface area of the fat and by causing clumping of the fat globules. They added that the smooth- ness of the ice cream is increased by increasing the diSpersion of the fat in the mixture. Dean (27) reported that when fat is present, homogenization destabilizes the proteins of dairy fluids and increases the pH. He attributed the loss of stability partially to the Change in pH and partially to the calcium ion. Dahle, Keith, and McCullough (21) re- ported that the destabilization of the proteins by homogenization also is true in ice cream mixes. The decrease in pH was attributed to the temperature increase during homogenization by Sommer and Menos (92). Dean (28) reported that in the presence of fat the stability of milk proteins, as measured by theaflcohol coagulation test, is greatly de- creased by homogenization. The clumping of fat globules in homogenized milk products was first noted by Mortensen (71). DePew (25) concluded that there are two types of viscosity, apparent and basic. He noted that an increase in homogenization pressure causes an increase in viscosity and an increase in the clumping of the fat globules. Early work by Doan (26) states that fat clumping is greatly stimulated in milk and cream mixtures by an increase in either the fat content or the homogenization pressure. However, he noted that the acidity of the plasma had little influence on fat clumping in milk and cream mixtures. Dahle (19) found an in- creasing tendency for the fat globules to clump as the ratio of the serum solids to the fat decreased. Reid and Garrison (82) reported that processing the mix de- creases the size of the fat globules and causes clumping, but they were unable to obtain any relationship between the size of the clumps and the pressure at which the mix was processed. They found the homogenizing pressure markedly affects the whipping ability of an ice cream mixture and increased pressure results in a greater ease of air incorporation. At the Missouri station, Reid and Skinner (87) and Reid and Russell (85) confirmed earlier work by reporting that an increase in homogenization pressure renders ice cream mix more receptive to the incorporation of air. The fact that mixes with a high viscosity incorporated overrun more slowly and in smaller amounts than those with less viscosity was- noted by DePew (25). wright (100) agreed, reporting that the whipping properties decreased as the viscosity increased. Hening (53) noted that the lower the homogenization pressure, the larger the fat globules. He also noted that viscosity increased as homogenization pressure increased. Reid and Moseley (84) and Reid and Russell (85) noted that homogenization lessened the melt down stability of an ice cream mix at summer temperatures. Wright (100) reported that as viscosity increases the rate of melt down is decreased and the manner is also influenced. Erb and Whitworth (34) observed that the higher the homogenizing pressure, the more rapid and smoother the melt down. Leighton, Leviton, and 'Williams (60) declared that viscosity is an indication of change in quality and physical action when only one factor is varied. Dahle (19) stated that the pH is lowered slightly when the homogenization pressure is increased from 2500 to 3500 pounds per square 7 inch. Leighton and Leviton (59) found that an increase in homogenization pressure increases stability and maximum overrun. Farrell (41) observed that a higher degree of protein stability is obtained when homogenization is attained without the use of excessive pressures. Erb and Whitworth (34) stated that the body is improved and a smoother and more rapid rate of melt downijiobtained When ice cream mix is processed at the higher pressures. They continued that the higher the homogenization pressure or the more often it was homogenized, the wetter the appearance of the ice cream when drawn from the freezer. Increasing the pressure or rehomogenizing the mix, according to Erb (33), resulted in a wetter appearance when drawn from the freezer. He attributed this condition to the thoroughness of the fat diapersion. It was reported by DePew (25) that a homogenization temperature of 1450?. prouuced a g eater viscosity of the mix after aging than one of llOoF. He attributed this to the greater diapersicn of the fat at higher temperatures. Doan (27) noted that heated plasma has an inhibiting effect on the production of fat clumps by the homogenizer. Dahle (28) found that clumping is decreased as the homogenization temperature is increased. He added that mix homogenized at lYOOF. as compared with lower temperatures whips faster and shows less clumping. Horrall (55) reported that processing the mix at higher temperatures gives better body and texture, decreases fat clumping and basic viscosity, and improves whipping ability. Leighton, Leviton, and Williams (60) ob- served that increasing homogenization temperature tends to reduce the amount of gelatin or milk fat necessary to produce the same viscosity. In later work, Leighton and Leviton (59) noted that an increase in homogenization temperatures accelerates aging undersnme conditions. {I} Reid and Scism (86) stated that emulsification, viscolization, or homogenization caused an increase in viscosity, while re-viscolization or re-homogenization decreased the viscosity. Martin and Dahle (67) have shown that two-stage homogenization reduced the clumping, decreased the viscosity, and increased the whipping ability of mixes. These findings have been confirmed by Hening (50) and others. Reid and Skinner (87) observed that an increaed pressure in a single stage homogenizer caused a uniform increase in viscosity and surface tension. They also noted that a reduction of viscosity with a second stage improved quality. They concluded that increaed.hommgenization pressures gave corresponding increases in smoothness, body resistance, warmth, and close texture. Working with.high solids mixes, Mack (63) found that three stage homo- genization entirely eliminated the problem of viscosity, decreased crumbliness, and reduced undesirable melting appearances. Olson and Fay (77) and Fabian (35) agreed that homogenization broke up the clumps of bacteria and gave an increase in the bacterial count as determined by the agar plate method. Caulfield and Martin (11) stated that no differences were observed in the results of the phosphatase test as a result of homogenization or freezing. Dowd and Anderson (29) reported that homogenization before or after pasteurization does not” affect the efficiency of bacterial reduction nor does it bring about any significant difference in viscosity. There have been a number of comparisons between the high pressure type homogenizer and other machines. Hening (53) compared pressure and centrigugal homogenization and found that low pressure homogenization gave similar results with respect to viscosity and size of fat globules. At the higher pressures, however, he noted that the viscosity and the 9 size of the fat clumps are increased, and also the mixes with a higher viscosity whip less readily. In a study of rotary and pressure machines, Dahle and Moss (23) concluded that both of the rotary machines tested gave satisfactory results as to body and texture, fat globule size, overrun, and clumping. Tracy and Hahn (94) found that the rotary type machine produces comparable results to the range of 1500 to 2000 pounds pressure on the standard machine. However, they reported that the rotary machine does not pro- duce as desirable results as the high pressure type in the range of 2000 to 3000 pounds pressure, when they checked fat globule size, viscosity, whipping ability, body, texture, and melt down characteristics. Other studies have been made in which sonic vibrations have been used to homogenize the mix. Anderson (1) compared sonic vibration to pressure homogenization and found that the freezing and whipping time of the mix compares favorably when either of the machines are used. He added that body and texture of oscillated and homogenized mix compared favorably with mixes made from the same ingredients, including gelatin and egg powder. Chambers (12) stated that sonic homogenization has pro- gressed to the point where it is possible on a commercial scale. Cole and 9mith (17) used a l per cent agueous solution of nile blue sulfate in an effort to determine the fat globule size and found that the red dye is soluble in the fat and the blue is soluble in the water faction. They recommended use of the dye as an aid for microscopic. work. Farrell, Walts, and Hansen (42) reported a method of examining five or more random fields and counted the globules of various sizes. ‘With this method, they developed an index number to give an indication of the efficiency of homogenization. 10 It was reported by Sherwood and Smallfield (89) that agitation causes a decided reduction in viscosity with an accompanying reduction in the size of the clumps of fat globules. Whitaker (97) observed that there are two types of viscosity and described a device that by mechanical agitation reduces the apparent viscosity to the basic viscosity. Hening (52) concluded that basic viscosity is a value secured under Specific conditions and is not a correct minimum value. He reported that mechanical agitation reduces the viscosity by partially splitting the fat clumps, and that different conditions of agitation vary in their effectiveness in Splitting the clumps. Leighton, Leviton, and Williams (60) using a sagging beam.method of determining viscosity noted that an increase in temperature tends to reduce the quantity of fat or gelatin necessary to produce the desired viscosity effect. They add that in a series where only one factor is varied, viscosity is an indication of change in quality and physical action of that factor in ice cream. Penczek and Dahlberg (79) reported that the hand emulsifier is more efficient and more practical than agitation to reduce apparent viscosity to basic viscosity. Protein Stability. Sommer and Binney (91) reported that the alcohol test is helpful in detecting milk that will coagulate upon heating. Martin (65) used for a test of protein stability a mixture of mix, water, and rennet solution. He agitated this solution and noted the time until feathering occurred. Dahle and Rivers (24) and Meiser (70) Suggested a test to determine protein stability. In this test they added 5 ml. of mix to 10 m1. of a mixture of 95 per cent alcohol and water. They reported the least concentration of alcohol necessary to just produce floculation in the 15 ml. mixture as the alcohol number. ll figing. Aging of the ice cream mix after processing is a practice widely followed in the ice cream industry. In early work with aging, hortensen (71) reported that aging for 24 hours increases the yield of ice cream and that aging the mix for 48 hours produced an additional but not as large increase in yield. Gregory and Manhart (45) found that aging helped in obtaining a greater overrun. DePew (25) observed that aging greatly increases the apparent viscosity of the mix, but that agitation, previous to freezing, in order to decrease the apparent viscosity, did not affect overrun or ease in obtaining overrun. Dahle, Keith, and McCullough (21) stated that aging 4 hours proves as effective as 24 hours with respect to whipping ability. Lucas (62) reported that the longer the aging period the greater the attainable overrun. Leighton and Leviton (59)*reported that aging will increase the whipping properties if the mix has been heated. The following investigators - martin, Swope, and Knapp (69); Sherwood and Smallfield (89); DePew (28); Reid and Skinner (87); Dahle, Keith, and McCullough (21); Lucas (62); and Hahn (47) - reported that aging the mix will increase the viscosity. Sherwood and Smallfield (89) attribute this increase in viscosity to the grouping of the fat globules. DePew (25) and Wright (100) differ in that they believe the increase in viscosity is due to the formation of a mechanical gel structure. Reid and Skinner (87) stated that the viscosity reaches its peak after 48 to 72 hours of aging. Hahn (46) noted that in a mix containing gelatin the viscosity increases over a 48 hour period. He added that cooling the mix rapidly to 40°F., in comparison to cooling rapidly to 70°F. to 80°F. and then slowly to 40°F., resulted in lower viscosity. 12 Martin (64) stated that aging materially improves the texture of low solids mixes but is of no practical value with high solids ice cream mixes. Horrall (55) observed that 4 or 24 hours of aging showed little effect on body and texture. Dahle, Keith, and McCullough (21) stated that a satisfactory body and texture is obtained after 4 hours of aging at 40°F., but 24 hours of aging gives some additional improve- ments in body and texture. Honing (51) concluded thatthe benefits derived from the aging of mix for more than 2 to 4 hours are of minor significance and little commercial value. Fay (43) stated that aging of the mix for fifteen to eighteen hours does not result in any material increase in bacteria count. Dahle, Keith, and McCullough (21) reported that 24 hours of aging at 40°F. results in a slight decrease in pH and no increase in titratable acidity. With reference to the phosphatase test, Hahn and Tracy (48) reported that holding mix at 40°F. for two weeks did not appreciably alter the phenol value. Studies at the hassachusetts experiment station resulted in the conclusion by Mueller and Frandsen (74) that higher aging temperatures of 68°F. improves body and texture, increases the viscosity, increases melting resistance, and slightly retards the rate of whipping. They noticed no measurable effect on the pH, titratable acidity, or bacterial growth. Mueller and France (73) reported that aging for 6 hours at 68°F. followed by l8 hours at 38°F., or aging at 38°F. for 24 hours does not increase the bacteria count materially. Mueller (72) attributed any benefits due to higher aging to the formation of gel filiments which in turn offered mechanical obstruction to the formation of large ice crystals. 13 Freezing. Freezing is an important step in the manufacture of ice cream and a number of investigators have reported on the various aspects of freezing. Hall (49) observed that the size of the ice crystals make the ice cream smooth or coarse, and that quick frozen crystals are small. He also stated that in freezing, the water separates from the mix and freezes out as ice crystals. Reichart (80) noted that the speed of the dasher has no appreciable effect on the rapidity of freezing, speed of whipping, or body and texture of the ice cream. Cole (13) stated that the rate of freezing materially affects the size of the ice crystals, but he was unable to find any correlation between ice crystal size and air cell size. Cole and Boulware (16) found that a good correlation between the ice crystal size and the smoothness of the ice cream can be expected. Munkwitz and Meade (75) reported that the rate of freezing is dependent upon the sharpness of the blades; the sharper the blades the faster the freezing time. They noted that dull blades caused coarseness in the ice cream. In tests at the University of Maryland, Farrell (40) found that freezing and whipping time are reduced 45 per cent by sharpening the blades. He concluded that dull blades are responsible for reduced capacity, poor air incorporation, coarse texture, and inferior quality. It was noted by Heyl and Tracy (54) that there is an inverse relation between the body and texture score and the drawing temperature. Dowd and Anderson (29) found that the body and texture of ice cream is more dependent on the method of freezing than on the method of pasteuri- zation or length of aging time. Hening (50) noted that freezing reduces the size of the fat clusters, but could not find any uniformity in the amount of reduction. 1h It was also observed by Reid and Skinner (87) that freezing reduces clumping, putting each globule in an individual emulsion. Dahle and Rivers (24) reported that the freezing process does not affect protein stability. It was observed by Leighton and Leviton (58) that there is a directly proportional relationship between the temperature and the overrun obtainable, 1.6., as the freezing temperature decreases there is a decrease in the overrun obtainable. Cole (14) calculated that in a normal 12.3 per cent butterfat mix frozen to 23.9OF., only 41 per cent of the water in the mix is frozen. Leighton and Leviton (59) stated that proper adjustment of the temperature-overrun relationship will lower freezing time. Leighton (57) stated that a maximum whip consistent with the existing temperature is attained in the batch freezer shortly after the refrigeration is turned off. The introduction of the continuous freezer resulted in investi- gations comparing the resultant ice cream of the batch and continuous freezer. Bradley and Dahle (7) observed that the type of freeZer, as it affects the drawing temperature, will affect the texture, size of ice crystals, and rate of hardening. They found, however, that atsimilar drawing temperatures, continuously frozen ice cream is smoother than batch frozen ice cream. Erb (32) stated that continuously frozen ice cream is superior to batch frozen ice cream because of the air cell size. Heyl and Tracy (54) reported that ice cream drawn at the same temperature on a counter, batch, and continuous freezer are equal in body determined organoleptically. It was reported by Turnbow, Tracy, and Raffetto (96) that aging the mix 24 hours will improve the body of continuously frozen ice cream and will aid in preventing ice separation during freezing. 15 Reid (81) observed that dull freezer blades results in impared efficiency, low heat transmission, increased freezing time, coarseness in the ice cream, and lower body and texture scores. He noted that smaller ice crystals give a warmer feeling in the mouth. Farrall (M0) noted that 23°F. to 24°F. is the best temperature for whipping and any deviation from that temperature reduces whipping ability. He observed that continuous freezers could whip sufficiently even at the lower freez- ing temperatures. Working with continuous freezers, Levowitz (61) re- ported that as the overrun is lowered the ice cream becomes more moist and finally ice lumps will appear. Forster (MM) stated that air can not be incorporated until the mix was partially frozen. The longer the time required to get the mix to the proper consistency, the less the time available for whipping and air incorporation. Fluctuating temperatures, reported Cole (13), will result in the melting of the small ice crystals and refreezing of the melted portion on the large crystals tending to make them larger. Bradley and.Dahle (7) found that air circulation, low drawing temperature, and low overrun reduce hardening time. They added that the more rapid the hardening of ice cream, the smaller the size of the ice crystals. Horrall (55) re- ported that ice cream stored at ~100F. has a better body and texoure than that stored at 10°F. Seism (88) noted that ice cream stored at -25°F. resists deterioration exceptionally well, the first noticeable effect being less of desirable body and texture. Hardening Ice Cream. In a study of the hardening of ice cream, Tracy and McCowen (95) found that the center temperature remains relatively con- stant for 5 hours and.then drOps to 00F. in 13 hours in a —18°F. hardening room. They added that the rate of hardening is dependent upon the area 16 and shape of the package, and that circulating air increases the rate of hardening 100 per cent. Hahn and Tracy (48) found that storage of ice cream at —20°F. for 12 weeks results in a decrease in phenol values for most of the samples. Arbuckle (2) reported that an increase in overrun tends to decrease the ice crystal and air cell size. Ice Crystal Size. In early work with photomicrographs of frozen ice cream, Brainerd (8) observed that the finer the divisbn of the fat globules the better the keeping qualities and the smaller the ice crystals in the ice cream. Dahlberg (18) reported that the air cells in homogenized ice cream average 60 microns. He could find no relation between the size of the air cells and texture. Cole (13) stated that the rotary microtome at ~18°F. gave the best results when sectioning frozen ice cream. Because of the great difference between the index of refraction of air and of ice crystals, Reid and Hales (83) suggested the use of an embedding material of alcohol and kerosene mixed to have a refractive index of 1.420 at 21°F. Arbuckle, Decker, and Reid (4) separated the crystals in ice cream and studied their optical properties using a petrographic microscope. In a study of texture and structure, Arbuckle (2) (3) described a technique to examine ice crystals. He reported that as overrun increases, the ice crystal and air cell size decreases. Keller et al (56) used polarized light to distinguish lactose and ice crystals by their optical properties. They used the same sectioning and embedding technique developed earlier at Missouri and outlined by Arbuckle (2). 1? PLAN OF EXPERILEEN T This investigation was limited to the study of processing methods and their effect on quality. Throughout the problem, only one factor was varied and the ice cream was tested to see how that one variable affected the quality of the resultant product. The mix used through- out the problem was prepared according to the same formula, thereby eliminating any influence which may be attributed to a change in the mix composition. A standardized method of preparation was used in each section so that the only variable would be the one processing method. The nature of this study was such that it was divided into sections. Consequently, each section was devoted to studying one of the following phases used in the processing of the ice cream: I. Pasteurization Temperature 11. Homogenization Pressure III. Homogenization Temperature IV. Aging Period V. Hardening Temperature The phases were studied in the above order since that was the logical sequence for processing ice cream mix under commercial conditions. A number of different factors are associated with the quality of the ice cream. Consequently, varied tests were conducted on the samples in order to determine quality. Among the tests that would determine the quality of the ice cream and would be affected by the processing methods were the following: 1. Acidity 10. pH Viscosity . Surface Tension Alcohol Number Fat Globule Size and Slumping Whipping Characteristics Body and Texture Score Melt Down Characteristics Ice Crystal Size 18 19 I. THE EFFECT OF VARYING THE PASTEURIZATION TEMPERATURE ON THE QUALITY OF ICE CREAM In these experiments all factors but one were constant, and the resulting product was tested to determine how that one variable factor affected quality. Pasteurization temperatures of 150°F., 160°F. and 170°F. respectively were used to pasteurize the mix, and the resulting product was tested to see how that variation affected quality. Procedure Ingredients agd_Composition g£_thg yix. The mix composition used throughout this investigation was as follows: 39.0 per cent total solids, 12.1 per cent butterfat, 10.9 per cent serum solids, 15.7 per cent sugar, and 0.31 per cent stabilizer. The sweetness of the mix was 15 per cent sucrose when the relative amount and sweetness of the various sugars used were considered. The ingredients used in the preparation of the mix included fresh cream containing 40 per cent butterfat; fresh skim- milk containing 9 per cent solids; roller process skimmilk powder containing 97 per cent milk solids; cane sugar; dextrose containing 92 per cent solids; Sweetose syrup containing 82 per cent solids; and Vestirine. Raw materials used in the preparation of the experimental mixes were obtained from the College Creamery. The following table shows the composition of themix used throughout the problem. Table 1. Composition of the Mix. Ingredients Pounds Pounds Pounds Pounds 5—P0unds ~Total _ Fat 5.5. Sugar Stab. Solids Cream 786 314.4 42.4 - - 356:3 Skimmmilk 1243 - 111.9 - - 111.9 Skim Powder 134 - 130.0 - - 130.0 Cane Sugar 273 - - 273.0 - 273.0 Dextrose 70 - - 64.4 - 64.4 Sweetose 86 - - 70.5 - 70.5 Vestirine 8 - - - 8.0 8.0 Total 2 00 314.4 2871.3" 407.9 82—0 1014 Per Cent 100 12.1 10.9 15.7 0.31 39.0 20 Prepargaftion 9.1; 3112 Egg _C_r_e_a__m. The ingredients used in the mix were combined in a 300 gallon Creamery Package Series .‘B steam vapor pasteur- Sizing vat and heated until all of the ingredients were dissolved and thoroughly mixed. Three portions were then separated from the large batch and placed into ten gallon milk cans. Cans containing the mix were placed in hot water baths and heated until a temperature of 15003.. 160°?" and 170°}. respectively were reached. The mixes were then held at the various pasteurization temperatures for 30 minutes. At the end of the pasteurization period, the mixes were cooled to 150°P. at which temperature they were homogenized in a Manton-Gaulin 25 gallon per hour laboratory homogenizer. The pressure used was 2500 pounds per square inch on a single stage valve with a breaker ring. Immediately after homogenization the mix was placed in milk cans which were immersed in a 50°F. water bath.. Following aging at )4063'. for 21+ hours, the mixes were removed from the cold storage room and frozen in a l-|0 quart Creamery Package Fort Atkinson Direct Expansion ice cream freezer. The mixes were frozen until the Draw-rite controller read 6 amperes at which time the ammonia was shut off. The temperature of the ice cream at this point was approximately 23.503. The ice cream was permitted to whip until an overrun of 90 per cent was reached. At this point samples were obtained directly from the freezer and placed in a hardening room at -10°I‘. where they were pemitted to harden at that temperature under still air condi- tions. In order to obtain overrun characteristics for the individual mixes, the ice cream remaining in the freezer was whipped for a period of 20 minutes. 21 m £2; Quality. Included in the tests for quality were the following determinations: acidity, pH, viscosity, surface tension, protein sta- bility, fat globule size and clumping, whipping characteristics, body score, melt down, and ice crystal size. These tests were conducted on samples taken before and after processing and after freezing and melting The procedures used in obtaining these data are explained in the following paragraphs. 1. Acidity. A 9 ml. sample of the mix was placed in a beaker and diluted with 9 m1. of distilled water used to rinse the pipette. Four drops of a one per cent alcoholic solution of phenolphthalein was added to the sample which was then titrated with a 0.1 N NaOH solution. The sample was titrated with constant stirring until a faint permanent pink color was obtained. 2. pg. The pH of each of the samples of mix was determined by means of a Beckman pH Meter, model C (Laboratory Hodel). equipped with a glass electrode. The potentiometer was standardized imediately before use with a standard buffer solution. All readings were made at a temperature of 20°C. 3. Viscosity. The viscosity of the samples was obtained by following the directions of Eimer and Amend (31). manufacturers of the Improved hacMicheal Viscosimeter used in these experiments. The following con- ditions were applied in standardization and use of the instrument. A disk bob was submerged to a depth of 3 cm. in the solution at 20°C, and the cup containing the liquid was revolved at a speed of 20 r.p.m. The I: (constant) for the instrument was determined by checking it against oils of known viscosity supplied by the Blreau of Standards, U. S. 22 Department of Commerce. The samples were tempered in a 20°C. water bath for two hours before the readings were made, and the resulting values in LiacMichael degrees were then substituted into a formula supplied with the standard oils and converted to centipoise. The samples were tempered in a 20°C. tempered water bath for two hours before the readings were made. For standarizing the instrument a disk bob was submerged to a depth of 3 cm. in a cup containing oils of a known viscosity supplied by the Bureau of Standards, U. S. Department of Commerce. After the k (constant) for the instrument was determined the resulting readings in Macmichael degrees were then substituted into a formula supplied with the standard oils and the readings were con— verted to centipoises. 14. Surface T nsion. A Many tensiometer was used to detemine the surface tension of the mixes studied. The procedure followed was that recommended by the Central Scientific Company, manufacturer of the instrument. In each case the tensiometer was standardized before being used, and the surface tension was determined after the mix had been tempered for two hours in a water bath at 20°C. 5. Protein Stability. The alcohol number of the mix was used as an indication of the protein stability. The procedure used was one sug- gested by Doan (2 7) and modified by Meiser (70). This procedure involved mixing in a test tube. 5 m1. of mix with 10 ml. of a solution of water and 95 per cent ethyl alcohol, and inverting the tube five times to insure complete mixture. The 10 m1. volume of water-alcohol solution remained constant but the ratio of alcohol to water was varied. This resulted in 15 m1. of mixed solution in which the amount of mix _ I (vitriol; .ll!l. 9- [Willi II rlll'¢(| "s‘lllftr toll: .ilrl. It‘. .I I n I. 5' t... 23 remained constant while the amount of water and alcohol varied inversely to each other. The alcohol number was the least amount of alcohol nec- essary to produce precipitation of the protein in the mixture. 6. 32.; Globule §_i_z_e_ 9&4. m. The fat globule size and clumping was determined by a direct microscopic examination of the mix. The microsc0pe was standandized so that the size of the fat globules could be observed at the same time that the sample was examined for clumping. The procedure used was a modification of one suggested by Doan (26). In the procedure used, the mix was diluted 1:100 with distilled water, prepared in a hanging dr0p slide, and examined directly with a micro- scope at 9701 magnification. Certain problems were encountered in the observations. Not all of the globules were in the same plane and the globules, particularly the larger ones. had a tendency to rise to the top layer. therefore, when examining the mix five fields were used and by moving the focus up and down and the average size of the fat globules and the degree of clumping were observed. The size of the fat globules was measured by a scale in the eyepiece of the microsc0pe. The relative degree of clumping was expressed from 0 to W depending upon the amount of clumping observed: 0 when no clumping was observed, + when clumPs of 2 to 5 globules were observed, H» when clumps of 5 to 10 globules were observed, +4-4- when clumps of 10 to 20 globules were ob- served, «no-4- when clumps of 20 to 50 globules were observed, and «Ha-+4- when clumps of over 50 globules were observed. 7. Vfliipping Characteristics. The whipping characteristics of each of the the mixes was determined by taking an overrun reading on the ice cream at one minute intervals for a period of 20 minutes after the 4'» -I-—~-..e 2h ammonia was turned on. In all cases the mix was frozen to a reading of 6 amperes on the Draw-rite controller which gave a drawing temperature of 23.50F. S. m _a_._n_d_._ We Score. The body and texture score was obtained for each of the samples of ice cream prepared in this experiment. The sam- ples were stored in a 40°F. hardening room until scoring and then placed at room temperature for a few minutes prior to being scored for body and texture organoleptically. In keeping with the standards set up by the Committee on Judging of Dairy Products, American Dairy Science Association, a score of 30 points was considered a perfect score. The same ingredients were used in each of the mixes; therefore the ice cream was not scored for flavor unless some notable difference in flavor of the dairy products was detected. 9. M 2911;. The melting characteristics for each batch of ice cream prepared was determined by placing 100 grams of ice cream on a wire screen having a 12 by 12 melt per inch. The ice cream‘was permitted to melt at a temperature of 25°F. (77°F.) for one and one-half hours. The melted ice cream was caught in funnels and directed into graduate cyl- inders, in which it was held for a period of time sufficiently long to permit the foam to collapse. The volume of mix collected in this manner was used as an indication for the rate of melt down. The appearance of the melt down was noted and recorded during the melting process. 10. Ice C_rystgl_ §_i_._§_e_. The size of the ice crystals was determined for each sample of ice cream by a direct microsc0pic examination of the frozen ice cream. The procedure used was modification of techniques suggested by Cole (1}), Reid and Hales, (83) and Arbuckle (2 ), and 25 necessitated preparing a thin section of ice cream with the use of a table model microtome. The sectioning was most successful after the ice cream had been hardened to a temperature of -10°F. to -20°I‘. The slices of ice cream were then placed on a slide and covered with an embedding material consisting of a mixture of alcohol and kerosene having a refractive index of 1.420 at 20°C. Using a microscope with a 1001 magnification, the size of the ice crystals could be measured with an occular micrometer in the eyepiece of the microscope. Since it was imperative that the ice cream remained firm during sectioning and examination, the above procedure had to be carried out at hardening room temperatures. Esssriseaial.fiesslis Effect 21; Pasteurization Tmerature 9_1_1_ idit . Samples of each of the mixes were obtained at various stages in the processing and tested for acidity. The results of the titrations are given in the following tablee Table 2. The Effect of Varying the Pasteurization Temperature on the Acidity of the Mix. Pasteuri zation' Per Cent Acidity ' Temperature ' Batch ' Batch ' Batch ' Batch ' Batch ' : fig: 0 J 1 M I R u U I Before Processi 10003, 0.225 % 0.230 % 0.2 a 0.226 % 0.230 3 After Processi 1500F. 0.235 0e235 002 0e220 0e232 1600p, 0.228 0.233 0.237 0.215 .0.230 170°r. 0.230 0.235 0.237 0.218 0.236 After Freezing 15oop, 0.2h0 0.232 0.234 0.214 0.223 1600p, 0.2km 0.230 0.238 0.215 0.227 17003, 0.24u 0.225 0.230 0.216 0.225 The results of the acidity determinations failed to show any tendency 26 for either a decrease or increase in acidity. Therefore, it was con- cluded that the temperature of pasteurization does not affect the Beiditye Effect 9_f_’ Pasteurization Tflerature _o_r_1_ p_H_. Potentiometric determi- nations on each of the mixes were made to detemine their hydrogen ion concentration. The resulting readings are given in the following table. Table 3. The Effect of Varying the Pasteurization Temperature on the pH of the Mix. Pasteurization' pH Readigs ' Temperature ‘ Batch ' Batch ' Batch ' Batch ' Batch ' I lgfi I g I m I ’ R I U I- Before Processing 100°r. 6.36 6.35 6.36 6.35 6.35 o 6 6 fits: lgrocessiéng6 6 6 150 F. .3 03 03 032 037 160°r. 6.35 . 6.35 6.35 6.3% 6.37 170°r. 6.35 6.36 6.35 6.33 6.36 .After Freezing 150°r. 6.35 6.3M 6.36 6.37 6.37 160°m. 6.36 6.36 6.37 6.35 6.37 170°r. 6.35 6.36 6.37 6.35 6.35 The above results shoved.that the pH variation was insignificant in these tests and would indicate that the pasteurization temperature has little influence upon the pH of the mix. Effect 9;; Pasteurization Temperature 9_n_ Viscosity. Viscosity deter- minations on the MacMichael viscosimeter were made on each of the batches of ice cream. The results of these tests are given in the table on thee following page. It will be noted that in all of the mixes the viscosity was appre- ciably increased by processing and lowered by freezing. The increase in viscosity of the samples due to processing was attributable to the 27 clumping of the fat globules induced by homogenization. Conversely, the agitation during freezing reduced the clumping, tending to put each globule in an individual suspension. The viscosity in the samples after aging varied inconsistently showing no trend to indicate that the viscosity was affected significally by the temperature at which the mix‘waS'pasteurized. Table 4. The Effect of Varying the Pasteurization Temperature on the Viscosity of the Mix. Pasteurization' Centipoise ' Temperature ' Batch ' BatCh ' Batch ' Batch ' Batch ' ' G' ' J ' Ii ' R ' II ' Before Processing 100°r. 76.1 102.2 46.2 47.7 36.8 After Processing _ 150011. 214.7 141.4 339.9 125.3 125.2 160°r. 205.7 230.1 279.7 146.3 122.7 ‘ 170°r. 197.4 266.6 323 .4 202.0 160.2 h After Freezing 4 ha 150011. 5.1 93.1 3. 51.5 .7 16021:. 46.6 81. 71.8 59.2 54.1 170 r. 45.9 88. 79.4 63.5 57.7 Effect QfLPasteuriggtion Temperature 2p Surface Tgnsion. At three times during the preparation, samples of the mix were secured and surface tension determinations were made on them. These readings are given in the table on the following page. The temperature of pasteurization apparently had no effect on surface tension; however, it was noted that the readings on the frozen samples tended to be lower. This probably was due to the reduction in the amount of fat in suspension as a result of partial churning by the freezer. 28 Table 5. The Effect of Varying the Pasteurization Temperature on the Surface Tension 0f the Mix. Pasteurization' games per cm. ' Temperature ' Batch ' Batch ' Batch ‘ Batch Batch ' g G I J I L I R I U I Before Processing 100°r. 48.3 46.4 46.2 46.6 43.4 After Pmcessing / 150°r. 46.3 48.2 49.2 49.2 43.3 160°r. 46.8 48.6 49.0 50.1 48.2 170°r. 46.9 48.1 48.8 50.0 47.9 After Freezing 150°r. 43.1 49.2 46.7 46.5 46.8 160°r. 41.7 48.2 45.8 47.3 45.5 170°r. 42.5 48.6 46.5 47.2 46.2 Effect 9;; Pasteurization Tegerature 23; Protein Stability. Alcohol numbers, as an indication of protein stability, were determined on each of the samples secured at various stages during preparation. The following table contains the results of the alcohol number tests. Table 6. The Effect of Varying the Pasteurization Temperature on the Alcohol Number of the Mix. Pasteurization' Stability: Alcohol Number ' Temperature ' Batch ' Batch ' Batch ' Batch Batch ' I E: I J I M I R I U I Before Processing 100°r. 7.4 7.3 7.6 7.4 7.4 After Processing 150°r. 7.2 7. 7.3 7.4 7.4 160°r. 7. 7. 7.2 7.3 7.3 170°r. 7.4 7.4 7.1 7.2 7.3 o 7 After" 5Freezing 6 1% Fe 0 O O 703 7.7 160°r. 7. 7-5 7-4 7-3 7.6 170°r. 7.3 7.5 7.3 7.3 7.5 The results of these tests show that the alcohol number of the mix had a tendency to be lowered as the pasteurization temperature increased: however, the decrease was relatively small. The results also indicate that the freezing process did not appreciably affect the alcohol number. 29 m 23 Pasteurization Temperature in Fat Globule Size. Each of the samples of mix was diluted and observed by direct microscopic exami- nation of a hanging dr0p of the mixture. The average size of the fat globules was determined by observing five or more fields and estimating the average size using the scale in the eyepiece of the microscope as a measure. fie results of the'examinations are given in the following table. Table 7. fie Effect of Varying the Pasteurization Temperature on the Fat Globule Size in the Mix. Pasteurization' Size of. Fat Globules in Microns ' Temperature ' Batch ' Batch ' Batch ' Batch ' Batch ' ‘ G ‘ J ' M ' R ' U ' Before Processing fifi 100°r. 4.0 4.0 3.5 4.0 3.5 After Processing 150°r. 1.75 1.75 1.5 2.0 2.0 160°r. 1.75 1.5 1.5 2.0 1.75 ; 170°r. 2.0 1.5 1.5 2.0 - 1.75 5 After Freezing 150°r. 2.0 2.5 2.5 3.5 4.0 160°r. 5.0 2.5 4.0 3.0 4.0 170°r. .0 2.0 3.5 3.0 4.0 fie mix, before being processed, had globules averaging 3.5 to 14.0 microns in diameter in all of the batches prepared. The processing of the mix resulted in a finer dispersion of the fat globules averaging 1.5 to 2.0 microns in diameter. There was, however, no tendency either to decrease or increase in size as the pasteurization temperature increased. fie freezing process resulted in an increase in the size of the fat globules, which probably was brought about by the mechanical agitation of the mix. Effect _0_f_ Pasteurization Temperatgi o_n F3}; Mpg. fie degree of fat clumping in each of the mixes was determined at the same time the fat 30 globule size was. noted. fie results of the observations of fat clumping are given in the following table. Table 8. fie Effect of Varying the Pasteurization Temperature on the Fat Clumping in the Mix. Pasteurization' Extent of Fat 01% I Temperature ' Batch ' Batch ' Batch ' Batch I Batch I ' G ' J' ' M ' B. I U I Before Processing 100°F. 0 0 0 0 0 . After Processing 150°F. * ‘ +4-4- m *4. 160229. +4- -I-I- In» +4-4- +4- 170 F. “, y” “w m 4.... After Freezing 150035 O «I- «I- + «I- 1600?. ‘ § ‘. + + 170°r. a I. . . .. In all of the samples it will be noted that there was no observable clumping in the mix before being processing. In all cases the processing of the mix resulted in clumping of the fat to some degree; however, there was no uniformity in the increase of clumping tendencies within or be- tween the various batches. Homogenization of the mix induced the clumping of the fat globules during the processing. fie agitation during the freezing process resulted in a decrease in fat clumping in all of the samples except one, (in which the original clumping was slight, but freezing did not completely eliminate the clumping. Effect 9_f_ Pasteurization Temperature 9_n_ Body .a_n_d_ Texture Score. fie body and texture score for each of the samples of ice cream made from the mix, pasteurized at the various temperaturesused, was determined organoleptically. fie resulting scores are given in the following table. 31 Table 9. fie Effect of Varying the Pasteurization Temperature on the Body and Texture Score of the Ice Cream. Pasteurization' Body Score s I Temperature ‘ Batch ' Batch ' Batch ' Batch ' Batch I Q: I J I M I B. I U I 150°r. 28.50 28.50 28.00 28.00 28.25 160°r. 28.25 28.25 28.00 28.00 28.25 170°r. 28.25 28.25 28.00 28.00 28.25 It will be observed that the body and texture scores for the ice cream prepared in this phase of the experiment did not exhibit any wide variation. and that the score of the samples within a batch had a maximum variation of only 0.25 points. It was concluded that the body and texture are not significally affected by the temperature of pasteurization. m 9_z_1_ Lsteurization Tegerature 93 Bag 9;: Egg 2913. A sample of each of the batches of ice cream was permitted to melt. following the procedure given earlier, to determine the rapidity of melting. fie amounts of liquid obtained indicating the rate of melt down are given in the following table. Table 10. fie Effect of Varying the Pasteurization Temperature on the Rate of Melt Down of the Ice Cream. Pasteurization' M5313 Down in Elf. ' Temperature ' Batch ' Batch ' Batch ' Batch ' Batch ' I G I J I M I R I U I 1mm. 30m. 3km. ggm. 37m. h7m. 160°F. 31 35 36 R6 170°F. 28 28 36 7 no fie results on the preceding table show that there was no consist- ency in the rate of melt down of the samples. In the melting process, all of the samples were observed to have a smooth, creamy melt down. No significant difference in the rate or manner of melt down was observed between or within the batches. fierefore. the conclusion that the 32 pasteurization temperature does not appreciably affect the melt down characteristics was made. M 21W W as M £22 LC stale... A direct microscopic examination of each of the batches was made to determine the size of the ice crystals. fie results of the examinations are given in the following table. Table 11. fie Effect of Varying the Pasteurization Temperature on the Size of the Ice Crystals in the Frozen Ice Cream. Pasteurization' Size of Ice Crystals in Microns I Temperature ' Batch ' Batch ' Batch ' Batch ' Batch I ' g ' J ' M I R I U I 150013". No no no 30 us 160°r. 1+5 1+0 1:0 30 m5 170°F. l+0 11-0 MO 35 )45 It was observed that the size of the ice crystals varied in length from 30 to ’45 microns. fie variation within the samples was small with no trend toward an increase or decrease in the size of the crystals. It was concluded that temperature of pasteurization is not instrumental in determining the size of the ice crystals. Effect 9;: Pasteurization Temperature 9_n_ th_e_ Whipping Characteristics. fie overrun percentages taken during the entire freezing process were recorded for each of the batches made. fiese readings that show the whipping characteristics of each of the batches and the average of all of the batches are plotted on the graphs on the following pages. Overrun characteristics of the various batches of ice cream were unusually similar. there being only slight variations in the rate and capacity of whipping noted in the different batches. fie uniformity of these results showed that the pasteurization temperature does not affect the whipping characteristics. Illllllllrlulrll «+500 Hop S66fl0<0 33 was sneer 0F vasvmc' THE PASTEL‘RIZATION Tszwms'wss on CW: RRUN CHARACTERISTICS 130 - J20~ 110 1'00 80' 70 60- 50 40 30 BATCH o' 14oF v . 1 1 v —. Y i f T ....................... ’35: r- .'.' I”___,a- .‘ / ./ ,/ .".}.’ L f / p / 1 / I F ’ 1 J ’ J l I L- , q I 7 j —4 J .1 .7 :7 A .7 .‘I p l I / / / / ' 150's, 4 o ...... 16°. F, ‘4 ---- 170'; r 1 1 L 4 _ , . k 4- ;: :‘ Time {linutes) o *1 dtso<§ W'iO‘QC) 321 THE EFF‘TC'I‘ CF VARYING T221". h‘xSTTIUIZIL’sITILh TELIPF‘RATURE 1 4C 130» 120 20 10 C ' C'VT'IIII’ITZI CI‘HED‘ICTZRISTICS f BATCH J ? Y Y T r f j f T 1 )wux’o'r -.-. «p ago- "I“ s (”’9 . l K. (C r ’ . /’ ' C. 1 L . r _150'r‘ ~ .0000... 160.}? ----- 170'F N h ‘30 H O 12- 1-1 16 18 20 Time (Minutes) fl-DOO HO’U flQ‘QNOdO THE EFFECT OF VARYIIG THE PASTRURIZATIOI TEMPERATURE ON OVERRUN CHARACTERISTICS BATCH u 1407 130» 120 110 IOOT 70~ ‘0' 30 >. ’10 Y V Y 1 —T Y I’oo-I'o.-'.’.‘q I, 1’ i I .‘ ’0 .' J I 4 I J j .4 I J 5 I I .4 150'F. ........... 160'E .1 ------ 170's l -2 L 1 J 4 c a 10~ 12 14 Tim. (linuteo) 35 ”(9‘6 ”300 5CWHO<0 36 THE WT or VARYING THE pasrsumzmrmw mmmuruss ow ovsssun CHARACTERISTICS arms a 140 Y Y Y fl w r V Y T 120» 310 100- r 90 80~ 70» GDP 50 40 r 30 2 ' —--— 150's ~ 000.000.160.F Jl 1 L 1 [ -----1':o‘,r c j l L 1 fl 0 2 “i 6 8 10 12 I4. 16 ‘18 20 Time (Minutes) Hay) (+390 DCflHO' o-".=n“‘-‘h ..O '..‘o° o . "" ’0 Z.’ ‘ 6 g f I . 1 . I , J i ' I -: O .1 O O O .1 50» + Y I f . WV .' '-—--1500 Pounds -°-'-° 2000 Pounds -°N~°u ZSJO Pounds - "-'-- 3000 Pounds .1 --~---- 3500 Pounds O 1 I 1 1 3 I 1 1 j n .1 0 4.- 8 10 12 3.1} 16 13 20 Time (Minutes) 56 H o*o HUGO :CiH'10'- '1 40 >- -——-3500 Pounds 30 s -°-°-1‘.OOO Pounds 20 “““”‘?500 Pounds s “nu-FOOD Pounds 101 a ‘"'“'3500 Pounds O l 1 1 L 1 1 L 1 ‘ 0 2 4 6 8 IO 12 14 16 18 3‘0 Time (Minutes) 58 Discussion of Results The results of the analyses show that the pressure of homOgenization wesinrfluential in determing the quality of the resulting ice cream. It will be noted that the most desirable homogenization pressure is influenced by a number of factors and must be determined individually for each case. This discussion will point out how the various factors governing quality are affected by the homogenization.pressure. The results of the examination of the mix indicataithat the size of the fat globules‘masreduced as the homogenization pressureflwasincreased. The reduction in size was probably due to the increased shearing action brought about by reducing the clearance in the homogenization valve. The freezing process resulted in an increase in the size of the fat globules. The agitation during the freezing process a parently brought about collision and coalesence of the fat globules. Although the size was not exactly doubled in all cases, it was noted that the increase in size was proportional to the size of the fat globules before freezing. The clumping of the fat globules was observed to be increased by an increase in the homogenization pressure. This phenomenon has been noted by several investigators, (25), (Rb), and (96). The increased charge on the fat globules caused by the adsorpted protein layer has been ad- vanced as an explanation of the reason clumping occurs. The freezing process reduced the clumping of the fat globules. The agitation_of freezing.apparently was sufficient to separate mechanically the fat agregates until slight or no clumping was observed. Attempts were made to prepare photomicrographs showing the degree of clumping. he brownian movement, depth of the samples,and rising of the samples, and rising of the fat globules prevented the obtaining of 1%.. . — .u 5M! .I..., r. 59 a clear representative photomicrograph of the samples, thus they were not included because they failed to give representative pictures of the samples. In all of the cases, the viscosity of the mix increased as the ho- mogenization pressure increased. Several investigators (25), (52), (8M), and.(o9) have noted a direct relationship between the viscosity and the fat clumping. This study showed that both the viscosity and fat clumping were increased by an increase in homogenization pressure. Although the viscosity is greatly influenced by the degree of fat clumping, other factors also affect the viscosity. This is born out by the fact that after freezing the viscosity tended to vary directly with the homogenization pressurevfidle the fat clumping was reduced to a minimum. Nevertheless, the main factor in determing the viscosity of the mix appears to be the degree of internal friction of the solid phase due to the clumping of fat globules. Several studies, (50), (63). (67), and (86), have shown that the fat clumping and accompanying viscosity were reduced by rehomo- genization or multiple stage homogenization. The results of the alcohol number determinations show that there was a tendency for the stability of the proteins to be decreased as the pressure of homogenization was increased. Doan (27) reported that homogenization lowered the pH which in turn brought the system closer to the iso-electric point of casein. In this study the pH readings failed to show any significant difference thereby offering no eXplanation regarding the change in protein stability. The melt down characteristics were materially influenced by the homogenization pressure. The rate of melt down and the smoothness of melt down were observed to increase as the homogenization pressure increased. 60 Other investigators, (34), (8M), (85), and (100), have reported similar fi-dings. The reason for the faster and smoother melt down has been advanced and involves the finer diSpersion of the mix constituents at the higher homogenization pressure and a correSponding effect on the gel formation. A tendency for the body and texture scores to increase as the homogenization pressure increased was observed. The differences in the scores recorded primarily at the lower level were not large, thus the homogenization pressure apparently does not gr atly affect the body and texture score. It was noted during the scoring of the samples that the body of the ice cream became more resistant and chewy at the higher homogenization pressures. he literature of approximately twenty years ago reports marked unprovements in body and texture as the homogenization pressure was increased. However, with the present mix composition and freezing methods, the benefits brought about by higher homogenization pressures are not as significant. The whipping capacity of the mt: was increased by an increase in the homogenization pressure, but the rate of whipping was not noticeabhr affected by the pressure of homogenization. Here again the literature of a decade ago has reported marked increases in the whipping preperties as the homogenization pressure increased, but the present manufacturing practices have reduced the importance of the pressure of homogenization, providing the fat globifles have been sufficiently reduced. Among the factors that tend to reduce the importance of homogenization are the present ingredients, stabilizers, whipping aids, hom genizer efficiency, and freezers. 61 III. THE EFFECT OF VARYING THE HOEIOGENIZATION TEEPERATURE ON THE QUALITY OF ICE CREAM The process of homogenization has become an indispensible step in the preparation of ice cream. mix. Various temperatures of homogenization have been recommended and many different practices are being followed. In this portion of the experiment, homogenization pressures of llO°F.. 130°F., 150°F., and 170°F., resPectively, were used and the resulting product tested to see how variations in the pressure of homogenization would affect the quality. Procedure In this portion of the experiment homogenization temperature was the variable. In all cases the ingredients in the mix, the composition of the mix, the methods of testing, and the tests to determine quality were the same as those listed on 19 to 25. In this study, the ingredients were combined and pasteurized at a temperature of 150°F. for 30 minutes. At the end of the pasteurization period, four representative batches of mix were removed and placed in 10 gallon milk cans. 'Ihe batches were heated or cooled in water baths, as was necessary to temperatures of llO°F.. 130°F., 150°F., and l70°F.. and then homogenized with a Mantan-Gaulin laboratory homogenizer using a pressure of 2500 pounds per square inch on a single stage valve with a breaker ring. The homogenized batches were placed into milk cans and imediately cooled to 50°F. in a cold water bath, and then aged for 21! hours in a 1$00133 cold storage room before freezing. 62 Experimental Re sult_§_ M 93 Homogenization ibmperature 93 Acidity. Each of the batches of mix was titrated with 0.1 N NaOH to see how the temperature of homogenization affected the acidity. Acidity determinations were made at various stages in the processing and the results are given in the following table . Table 22. The Effect of Varying the Homogenization Temperature on the Acidity of the Mix. Homogenization' Per Cent Acidity ‘ Temperature ' Batch ' Batch ' Batch ' Batch ' Batch ' I D I H I I I I. I v I Before Processing 100°r. 0.235 % 0.225 %r 0.230 % 0.230 i 0.230 % After Processing 11003. 0.2u0 0.232 0.232 0.220 0.235 130°r. 0.2h0 0.235 0.232 No.222 0.231 150°r. 0.2h5 0.230 0.235 0.22 0.232 170°r. 0.238 0.232 0.235 0.22 0.232 After Freezing 110°r. 0.2u5 0.2 6 0.228 0.223 0.235 130°r. 0.2h0 0.2 0.226 0.220 0.232 150°r. 0.2u2 0.233 0.232 0.221 0.232 17003. 0.2h0 0.2u2 0.228 0.225 0.232 'Ihe results of the acidity tests show that the variations were inconsistent and 'failed to show any tendency to increase or decrease with the homogenization temperature. was homogenized apparently did not affect the acidity of the mix. Effect 9;; Homogenization iemperature g_n_ ELL EEhe temperature at which the mix The pH of each of the samples was determined to observe the influence of homegenizat'ion temperature on the pH. ihe results of the potentiometeric readings are given in'the following table. 63 Table 23. The Effect of Varying the Homogenization Temperature on the pH of the Mix. Homo genization' pH Readings ' Temperature ' Batch ' Batch ‘ Batch ' Batch ' Batch ' I D I H I I I L I v I Before Processing 100°r. 6.33 6.37 6.36 6.37 6.35 After Processing 110°r. 6.35 6.36 6.35 6.3M 6.3 1300r. 6.33 6.3 6.3 6.3M 6.37 150°r. 6.3h 6.37 6.35 6.36 6.36 170°r. 6.3u 6.36 6.35 6.37 6.36 After Freezing 110°r. 6.3M 6.37 6.36 6.35 6.35 130°r. 6.35 6.36 6.3 6.36 6.36 150°r. 6.35 6.35 6.35 6.36 6.37 170°r. 6.33 6.35 6.37 6.36 6.35 5116 results of the pH readings showed very little variation with no tendency to increase or decrease as the homogenization temperature was changed. It is evident that the temperature at which the mix was homogenized had little effect on the pH of the resulting product. Effect 91 Homogenization Temperature 9}; Viscosity. Viscosity determi- nations on each batch of mix were made on a Macmichael viscosimeter following the procedure given earlier. The results of these tests are given in the following table. Table 21+. The Effect of Varying the Homogenization Temperature on the Viscosity of the Mix. Homogeniation I Centipoise ' Temperature ' Batch ' Batch ' Batch ' Batch f Batch ' I J.) I H I I I L I v I . Before Processing 100°r. 35.7 76.1 102.3 2h3.5 36.8 After Processing 110°r. 2 1.h h92.6 55h.6 h92.6 319.6 1300r. 2 .9 329.h 508.5 M63.u 177.1 150°r. 232.2 21u.7 223.2 391.0 125.2 170°r. 230.3 188.6 207.2 316.8 110.9 After Freezing 110°r. 5n.9 85.0 88.0 93.1 53.0 130°r. 5 .0 82.7 86.5 92.1 52.8 150°r. .5 92.2 93.1 81.2 us.7 170qr. 52.2 9h. 85.7 7h.6 53.6 61+ The viscosity of the mix was greatly influenced by the temperature I _ . 4 , . . nu . . . . . . a . . . r _ a A ... . o I . I . ~ . t ,. L . . . . I _ I _ . . ~ . o . 5‘ ' 1 . e v A ,1 > J , u \. . C . L . . a . .. . a . .. . , . . . a! . . , I ~ . 4 . . _ . a. ., , . , ( . c l .. n g . 120 SUMfiARY.AND CONCLUSIONS Results obtained in this study indicated that an increase in pasteurization temperature resulted in a slight decrease in the protein stability but had no appreciable effect on the other quality tests. These determinations included the acidity, pH, viscosity, surface tension, bocy and texture score, melt down characteristics, size and clumping of the fat globules, ice crystal size and whipping characteristics. Since the quality of the finisheo product showed such slight Variation, it was concluced that the pasteurization temperatures used in this study were not important in determining the quality of the resulting ice cream. An increase in the homogenization pressure on a single-stage valve resulted in an increase in the fat globule clumping, viscosity; surface tension, body and texture score, and rate and smoothness of melt down. However, a decrease in the fat globule size and protein stability were obtained by an increase in the pressure of homogenization. Other factors that were not affected were the acioity, pH, and ice crystal size. Thus,homogenization pressure is iMportant in determining the quality of the ice cream; howevergpresent mix composition, stabilizers, whipping aids, homogenization efficiency, and freezers have reduced the importance of the pressure that is used, providing fat globule size has been reduced sufficiently. The viscosity, fat globule clumping, and rate and capacity of whipping Were increased by a decrease in homogenization temperature, while the rate of melt down was noted to be decreased slightly. However, the temperature of homogenization had no noticeable effect on the acidity, 121 pH, protein stability, surface tension, body and texture score, and ice crystal size. Since the temperature of homogenization will be governed largely by the equipment available, the viscosity of the re- sulting mix will be the limiting factor in determining the lowest temperature at which the mix can be homogenized under commercial con- ditions. An increase in the length of the aging period of the mix resulted in an increase in the viscosity and rate and capacity of whipping with slight increases being noted in the rate and smoothness of melt down and body and texture score. However, the length of the aging period had no significant effect on the acidity, pH, surface tension, protein stability, fat globule size and clumping, and ice crystal size. In this problem.the benefits due to aging were not great; therefore,it was concluded that aging of the mix, unless it is conducive to plant efficiency, is of little commercial value. Freezing the mix reduced the viscosity, surface tension, and fat globule clumping, increased the size of the fat globules, but had no apparent effect on the acidity, pH, or protein stability. Continuously frozen ice cream CONpared with batch frozen ice cream”hand1ed in the same manner except for freezing,had a smoother texture, smaller ice crystal size, and slower rate of melt down. Consequently, other factors being constant, continuously frozen ice cream was found to be superior to the batch frozen product. Reducing the temperature of hardening resulted in an increase in the rate of hardening and a decrease in the rate of melt down and ice crystal size. The rate of temperature decline was dependent on the hardening temperature and was not significantly affectedlnr the type of freezer used. The improvement in quality brought about by the increased 122 rate of hardening led to the conclusion that a decrease in the hardening temperature resulted in an increase in the quality of the resultant ice cream. (1) (2) (3) (4) (S) (6) (7) (8) (9) (10) (11) (12) LITERATURE CITED Anderson, E. 0. 1936. Sonic vibration of ice cream mixes. Proc. 36th Ann. Conv. Intern. Assoc. Ice Cream Mfrs. a: 126. (Abst.) Jour. Dairy Sci. 2_g: A98—99, 1937). Arbuckle, W. S. 1940. Microscopic and statistical analysis of the texture and structure of ice cream as affected by composition, physical properties and processing methods. Mo. Agr. Expt. Sta. Res. Bul. 320. ' Arbuckle, W. S. 1947. A microscopic study of ice cream texture. Jour. Dairy Sci. 32: 537. Arbuckle, W. S., Decker, C. W., and Reid, W. H. E. 1939. The use of the petrographic microsc0pe in studying the different types of lactose crystals as they occur in sandy ice cream. (Abst.) (Jour. Dairy Sci. g: 419. Armstrong, T. V. 1940. 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