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' -V 1 Q. L, I V 1 ’ ‘a ‘ a ‘ s~ ipsrisqeieotrtcaeratin.piue-fle1orzwaes).fi A . . - v e . ' e ' . . . a . ‘- I A . 0 . e . . s‘ _ 5 t a u - l—- -I‘- . -l*-I—— —-I I‘ l- “ hit" or “£701 0 “I as h." '—‘ I w I . a .I .‘A ‘ l‘l- _-ll-- i—n — — 16 line can be read in ounces of gelatin swell. They found that about two out of ten "swell readings" were dispro- portionate with their Jelly strength. They consider this test unreliable. Clarity. many writers claim that clarity is a very good test for quality in gelatin. manufacturers also place much stress upon this in their advertising. However, no one has proved that the clearer the solution, the better the gelatin. Clearness is merely an indica- tion that the gelatin manufacturer has removed from the colloidal gelatin other finely divided or colloidal matter which wouldmake the gelatin turbid. A light colored gelatin is usually conceded to be derived from high grade stock while a dark color is attributed to heating too high, improper boiling, or making from inferior_stock. Hall and Route (17) state that this is not the case; that color is due to the bleaching or lack of bleaching of the gelatin. This would lead to the conclusion that clarity and color are quite insignificant factors in determining the quality of gelatin. 0925, many gelatins have unnatural, gluey, or putrid odors which make them quite undesirable for consump- tion. According to Hall and Houtz (17), such products should be barred from any food such as icecream. They find that gelatins giving off such odors usually represent products which are high in bacteria and which are made from inferior stock. Burke (16) supports these other investigators in 17 their stand that gelatins with strong odors should not be used. He states that gelatin solutions can best be tested at 1406 to determine the presence of undesirable odors. ‘Ash; According to Hall and Houtz, the ash content is usually determined by heating two grams of gelatin in a large platinum crucible. This test is used only by chemists in analytical work, and is of little practical value to the ice cream maker. It merely discloses impurities or careless- ness in manufacture, and has no relation to other tests which indicate the strength of a gelatin. Acidity. The view has been advanced by many writers on gelatin that poor quality is associated with high acidity. tatements to this effect are often found in text books, but like other writers, these authors present no experimental data to substantiate their claims. The reason given for the undesirability of acidity in gelatin is that the acidity of the mix will be raised, thereby increasing the danger of curdling. Burke (33) con- ducted experiments adding various amounts of high acid gas- tins to sweet milk. He found that quantities of gelatin of 0.5 to l per cent would not cause curding of sweet milk, but it did increase the acidity of'the milk to the danger point. Lucas (34) found that when milk, instead of water, is used as a solvent for gelatin in ice cream making, those gelatins of high acid content often cause curdling. 18 Hall and Houtz (25) state that the greatest Jelly strength and viscosity are stained at or near the netural point. The results of Sheppard and Sweet (27) agree with this. They have definitely found a maximum of viscosity at pH7 to 9, and the indications are that the same is true with Jelly strengths, but they are not yet satisfied with the relatonship found between these two. There are two general methods of testing gelatins for acidity, the hydrogen-ion determination and neutrali- zation with sodium hydroxide. For strictly scientific work, the hydrogen-ion determination is the better method,. but costly apparatus and technical training on the part of the operator are required. This test is applicable only to research laboratories or large ice cream plants which employ a chemist. A test which is based on the neutralization of the acid in gelatin by sodium hydroxide is a modification of the Mann's acid test (35), employed in creameries in testing cream for acidity. In conducting the test, the acid content of the gelatin is considered equivalent to a like amount of hydrochloric acid. The method given by Burke (16) has been found to be in error, due to a mistake in his formula. By the corrected formula, the percent of acid in gelatin may be coaputed as follows: 0.0 n/lO alkali used x .00365 x 100 8 percent acid gms. gelatin used Burke (16) found that testing the gelatin in a 10% solution 19 at 1400 F. gave very good results. The work which has been done on acidity seems to indicate that excessive acidity in gelatin is undesirable, because it endangers the curdling of the ice cream mix and it lowers the Jellying power of the gelatin. Heisture. The percentage of moisture in gelathn, according to Hall and Houtz (17), may be determined by heating a weighed amount of gelatin to constant weight at 100° C. Burke (33) states that different samples of gelatin vary in moisture content fnom 10 to 17 percent, and the higher the grade of the gelatin, the more moisture. This is no doubt due to the fact that a good grade gelatin can absorb more water than one of a poorer quality. The work done on moisture is insufficient to draw any conclusions, but since the manner of storing the product and the length of holding could vary the moisture content considerably, it seems that this test would not be particu- larly valuable. Metallic Impurities. Tests for metallic impurities in gelatin are too complicated to be conducted in most ice cream plants. Since the state and federal pure food laws amoly protect the ice cream maker from this point of view, there is no need of him conducting these tests. The federal law requires that gelatin shall not aantain more than 30 parts par million of COpper, 100 parts per million of zinc, 20 parts per million of lead, 1.4 parts per million of arsenic oxide, and 350 parts per million of sulphur 20 dioxide. Storage. Hall and Houtz (l7) conclude from their experience with gelatin, that it may be kept in dry storage without danger of deterioration from either atmospheric, conditions or bacterial growth. This makes it necessary to exclude only flies, dust, etc. in storage. If a gelatin deteriorates in storage, when these cinditons are cared for, it is an indication that the quality was inferior. Miscroscopic:_ It has been found possible by Hall and Houtz (17) to grade gelatin fairly accurately by means of the miscroscope. They found that particles of low grade gelatin appeared glassy, having smoothly, rounded surfaces and little, if any, line formation. Throughout the mass were found dark yellow tints. The surface often showed a rough structure. High grade gelatin particles showed a beautiful, wave-like, delicate line formation of the fractured surfaces. They were more clear, showing an absence of yellow tints. The particles were more uniformly pene- trated by light rays, seldom showing extremely dark sections or glassy surfaces. These workers found that some gelatins do not lend themselves to this test and they do not cnnsider it universally applicable. Melting Test: Several investigators have Judged the quality of gelatin by the resistance to melting of ice cream in which it is an ingredient. Williams (18) placed two, three gallon cans of ice cream, one without gelatin and the other containing the normal amount, in an ordinary 81 ice cream cabinet in a warm.room.for 48 hours. At the end of that pried, the ice cream containing no gelatin had lost its identity; while the sample with no gelatin was unchanged. Ilnhart (19) also used this test in his experi- ments. He froze ice cream with no gelatin, poor quality gelatin, good quality gelatin, and very good quality gelatin, and melted bricks of'each at 86° 1. His results are given on the accompanying table. Hall and Heat: (17) found that gelatin does not retard melting in ice credm. They conducted their ex- periment in a manner similar to that of Iilliams (18), but found slight difference in the melting of the two. Irom.the data presented, it seems that opinion is divided as to the effect of gelatin.upon the melting of ice cream. However, the maJority of investigators feund that ice cream.without gelatin melts faster than ice cream with gelatin. Jelly value fast. The Jelly value tests,as described by Burke (16), Turnbow (so), and Parfitt (21) are all essentially the same. 'Conoentrationsof the gelatins are prepared in test tubes, ranging usually from.0.4 percent to 1.0 percent. The gelatin is dissolved in a water bath.at 140° F., and is then cooled down to 60° 1. After this temperature has been maintained for some time - at least 30 minutes - the tubes are inverted to note the minimum concentration which has solidified sufficiently to not run out. no UGO mm.mw m~.om mm.mm mm.a~ umwfi Inga oma pd mm.mm m~.:m mm.m~ mm.mm bop: lads om dopama mo.ma ma.:m ~m.mm mm.mm mops lads ow Bdmho edema 00H mo commandmom mcapao: one oo.w mm.ma mo.om w:.©m mend Iaae om so” mm.m mw.m m:.:a mm.ma mopfi lads . o: 9200 mm.o mm.o mm.m ow.m nova lawn om Hmm napsflmw hpfiaosu voom knob ......capdamm hpaamnc neoo ......n«pdflow hpaamsu noon ..........AKHB HOHpGoov qflpmamw oz madman» Icoo scone 00H no ahpaaou no occasflugH opapaflom 23 ill writers seem to think this a very good test, but the large number of weighings required make it de- cidedly tedious. . rreesing rest. Turnbow (20) describes a test for gelatin.aherein.definite strength solutions are frozun. and the frozen.product examined physically. He found.that poor gelatins make long, spiny crystals, ihile good grades make small, mealy crystals. It seems that this test could hardly be very accurate in rating gelatins similar in quality, and also, some gelatins, because of various reasons, might not lend themselves to this test. this test, then, could hardly be considered very satisfactory. leltigg rest. rho melting point of the Jelly of a givmn gelatin has often been regarded of importance in determining it's value. Bogus (36) has found the melting point and jelly strength to be parallel functions. rurnbom (20) has devised s simple melting test. Es places boaters containing Jells at the same tempera- ture in,a water bath at 100° r. and maintains this temera- ture in the bath throughout the experiment. mhe time that each sample requires to assume the liquid state is takmn. He found that this test gave very good results. Ihe investigators of today have quite generally decided that, among the tests for gelatin, the Jelly strength test reigns supreme. rhroughout most of the published work, other tests are compared with this test as being the authentic one. Ehe general opinion is, that a Jelly strength test, along with some kind of s bacterial count, gives a very good idea of the value of a gelatin. gacterial count. Studies have IhOIl that ice cream may be highly contaminated with bacteria. Since large numbers of bacteria are always undesirable in any dairy product, the ice cream manufacturer should reduce the number of organisms in his product as much as possible. A few cities have passed bacterial standards for ice cream, and others are studying the situation in order that an equitable ruling may be made. Ihe studies of Hllenberger (37) and Hammer (38) showthat milk, cream, and condensed milk are the most prolific sources of bacteria. they found that this con- taminaton could be greatly reduced by pasteurization. Bincsthese products are the chief ingredients .of ice cream, and they are quite consonly highly infested with bacteria, it is logical that the.bscterial flora of ice cream should consist essentially of these organisms found in them. Ayers and Johnson (39) examined in Washington, D. 0., 94 samples of ice cream during the simmer months and 91 samples during the winter months. In the summer, they found the average count to be 37,869,907, with a 25 maxium count of 610,000,000 and a.minimum of 120,000. In.winter, the average count was 10,388,288. the mazfllmm 114,000,000 and the minimum 13.000 bacteria per cubic centimeter. These investigators found that there were five groups of bacteria in ice cream. the percentages of the various groups, together with the calculated number and percentage of each is given in the following table: Bummer Samples Iinter Samples Bacterial Avera s Average ' Average Average Groups no. 0 group no. of group bacteria percen~ bacteria percen- fiper c.c. tag! per cc. tags. Acid-coagulating 18,861,806 49.88 3,803,728 30.8d Acid-forming 7,844,616 80.78 3,960,641 38.03 Alkali-forming 704.195 1.86 663,048 5.42 Pcptoniming 5,156,619 13.62 8,171,138 .OeOO fetal 31,859,909 100.00 10,388,888 100.00 lhe bacterial groups have much the same relation to each other in the winter and summer samples. the summer. samples showed a higher percentage of the acid coagulating group and.a lower percentage of the alkali and peptonising groups than.did the winter samples.- However, since there at was a lower average count in the winter, there were fewer of these last two groups than in the summer samples. as forming bacteria of the colon asrogenes group were determined on litmus-asparagin agar on 88.33 per cent of the samples tested. The average number in the entire series of samples was 16.898 per cubic centimeter. fhe presence of any considerable number of members of this group in dairy products is looked upon with suspi- cion, since 3. typhous belongs to this group and it is associated with fecal or decaying matter. Hllenberger (37) and Hammer (38) found that there is no radical change in the total number of bacteria in ice cream during storage. Hllenberger reports a slight decrease during the first two to four days, with a more noticeable increase and then a corresponding decrease between the fourth and twenty-first day. after which time, a falling off in numbers was again noted. Hllenberger found that aside from the utensil contamination, which is negligable, there is usually a great increase in the number of bacteria resulting from the freezing process. This is probably due to the break- ing up of bacterial clumps. He found an average increase of 48% in bacterial count due to the freeaing process. Gordon, Prescott, Hein‘mann and Peace (40) obtmed similar results.) ‘ . - to determine the importance of gelatin as a source of bacteria in ice cream has been the object of consider- 27 able research. lbny investigators have found that gelatin ccntains large numbers of bacteria. However, the effect cf'these organisms on the final count in the ice cream is not established. Hllenberger (37), Hammer (38), Gordon (41), Parfitt (42), and Brannon and Tracy (as) have shown that different brands ongelatin vary widely in the number of bacteria they contain. Hammer examined a number of samples of gelatin and after dissolving them with.gentle heat, plated them on agar. The following table shown the variations which he encountered: Sample Bacteria Bacteria in l c.c. number per Gram ice cream due to gelatin 1 113,000,000 555,000 2 14,000,000 10,000 3 36 0.2 4 4,200 81 6 85,000 486 the results in column three were derived by multi- plying the number of bacteria in a gram of gelatin by .006, since Cami gelatin is commonly used in ice cream. fhis calculation means little, since the volume relations and the number of bacteria killed by heat are ignored. fhe variations in bacterial count of different gelatins as reported by Hammer compare very favorably 28 with variations reported by other experimentialists. Brannon and Tracy (as) found that, in general, the grades within the different brands ran fairly uniform in bacterial count. This lead them to conclude that the method of manufacture is a very importsit factor in the number of bacteria present in gelatin. Parfitt (42) found the organisms in gelatin to be resistant to heat, cold, and drying to a marked degree. He found Bacterium coli in all samples examined, the total count being more than 6,000 organisms. This organism is associated with fecal and decaying matter, and, as ex» pressed by Parfitt, to find Bacterium.coli in our city water is considered serious.) Parfitt also found another type of organism.predominant in gelatin, the liquifier or protein digesting organism. Its presence is highly un- desirable because it breaks down the protein into lower protein compounds as amino acids, and renders the gelatin useless as a colloid and in Jellying power. Brannon and Tracy (43) found that heating gelatin to 140 and 160° F. groatiy reduces the number of bacteria present, even though the gelatin.may be highly contaminated. fhe efficiency of pasteurisstion seems to be greater in a water solution than in.a skimmilk solution. Brannon and Tracy (43) and Hammer (38) concluded, as a result of’their studies, that the addition of gelatin to ice cream results in a slight increase in the number of bacteria, and that 29 the use of high connt gelatin is undesirable. Iron a review of the data presented on bacteria in ice cream and the effect of gelatin on the count, it is concluded that both ice cream andgelatin contain large numbers of bacteria; that it is very desirable to keep the bacterial count of; ice cream as low A ' as possible; and that the use of high count gelatins should not be permitted in ice cream making. 50 EXPERIMENTAL WORK Object of Experiment The primary object of’this experiment was to de- termine the effect of viscosity of the mix upon the qual- ity of ice creams of uniform swell. Plan of Experimental Work Procedure. Inasmuch as gelatin is an essential ingredient of ice cream and causes in part the viscosity of the. mix, this study of viscosity has been concerned chiefly with gelatins. In order to study the effects of different gela- tins on the mix, seventeen lots of gelatin were obtained from thirteen different manufacturers and distributors. fhree grades were secured from one company, two from another, while one grade each of the other braids were obtained. Many! of these proved to be of extra high qual- ity, while others were only fair, and others, inferior. However, since the purpose of this work was not to de- termine the best quality gelatin on the market, but rather, to compare different gelatins with their differing viscos- ities and their relative influences upon ice cream, the wide range in quality of thegelat ins gave a very satis- factory group to use in conducting the work. 31 The work was divided into two parts or divisions: Part I, the freezing experiment. It was in thil work that the primary viscosity determinations were made. The melting test, employed to determine the true worth of the gelatins in the ice cream, was included. Part II,:gelatin quality determinations. This con- sisted of several tests for gelatin which were employed upon the seventeen samples. These mere then compared with the melting test to determine their value. Part I Freezinngxperiment In order to determine conclusively the effect of the seventeen different gelatin samples on ice cream, an ice cream batch was prepared and divided into seventeen portions of 22.6 pounds each. To each of these individual mixes 0.12 of a pound of the different gelatins was added, after having been dissolved in water and made up to 1.5 pounds. This gave seventeen, twenty-four pound ice cream batches which were of exactly the same composition, other than.containing different kinds of gelatin. The mix was composed of cream, skimmilk, skim-milk powder, cane sugar, and the gelatin-water solution. The computed composition of the mix was as follows: 32 rat................................12.00 1: 11111: solid-s not fat................11.00 1: Sugar..............................14.00 i 8e1atin............................ 0.6 $ Total solids.......................37.6 i The batch was made up in a pasteurising vat. The skim-milk powder and sugar were mixed together and added to the skimmilk and cream. The mixture was then pasteu- riaed at 146° for thirty minutes, after which it was immediately cooled deem to 110° r., viscolised at this temperature at a pressure of 1600 pounds and run over a surface cooler, where it was cooled to 70° 2. with cold water. The batch was then divided into seventeen mixes of 22.6 pounds each. In the preparation of the gelatin, 0.12 of a pound of each brand was weighed out. This was made up to 1.6 pounds by the addition of cold water. It was allowed to soak for 16 minutes, after which it was put in a water bath, the temperature raised to 160° 1., and the gelatin thoroughly dissolved. The solutions were immediately .added to the respective ice cream mixes. The mixes were aged for 48 hours at 36° F. Samples-were then taken for viscosity determinations. The mixes were frozen in a horizontal United States freeaer. The ice cream was dram off at an over run of 80 percent, as determined by the lioJonnier over-run tester. A quart brick and a pint container of each 33 ice cream were taken, the former for the melting test, and the latter to be scored for texture and body. The viscosity determinations were made by means of a Stormer viscoshmeter. This is an instrument in which a cylinder is caused to rotate in the liquid under examination, through the influence of’a weight. As the rotation of the cylinder under the influence of any given weight is assumed to be proportionhl to the viscosity e” of the liquid, the time is seconds taken for 100 revolu- tions of the cylinder is used as the measure of viscos- ity. water is taken as unity, therefore the quotient obtained by dividing the time taken in water gives the relative viscosity in terms of water. Samples of the mixes were taken for the viscos- ity determinations immediately before they were frozen, and tested without delay. In conducting these tests, a 102.49 gram weight was used. A temperature of 20° 0. or 68° 1. was maintained. ' The viscosity ”erminations were made only on the third, fourth, and fifth mixes. hr.:ni11er, of tbs chemistry Experiment station, Michigan stste College, made these tests. He considered the results of the three determinations so conclusive that further work on this phase of the problem was considered unnecessary. Irom the observations made in conducting the viscosity tests, it was noted that stirring the samples 34 materially affected the resulting viscosity readings. Accordingly, mix 6 was treated in varying ways to de- termine the effect of stirring upon viscosity. The samples were stirred in the usual manner, in adjusting the temperature to 20° 0. The readings were then made as usual. Some of the samples were tested three or four times, to note the effect of the revolving cylinder on the viscosity. Other samples were stirred vigorously after the first viscosity reading, and then.read again. Part of the samples were only stirred slightly after the first agitation to note the effect of this treatmmt, while others were stirred vigorously, allowed to stand a few moments, and then.stirred slightly. These results are later presented in tabular form. 1 The ice cream samples were scored for body and texture. a sample having ideal body and texture was given a perfect score of 25. To merit a perfect score, it was necessary that the sample be firm, free from air bubbles, ice crystals and sandiness: it could not be snowy, powdery, or spongy; it must resist melting and have 'body' when melted in the mouth; it must cut a clean bore and pull out with comparative ease when the trier was inserted. Since only very high quality gela- tins could produce an ice cream capable of meeting these requirements, it was considered a very good test for quality in gelatin. 36 The ice cream samples were placed in the sore room immediately after freezing and were kept there approximately a week, when they were withdrawn and scored. The samples were scored by Professor P. 8. Lucas andthe writer. ' The Melting Test, which consisted of melting down the quart bricks of ice cream after they had been in the zero room for three days, was considered by far the most important part of the experismnt. This test was used as the confirmatory test in determining the best gelatin. It gave definite results as to which gelatin.wms most capable of producing an ice cream which could best resist melting. In conducting the melting test, a wire screen with oneeeighth inch mesh was stretched on a wooden frame, 2-1/2 by 6 feet. This frame was placed two and a half feet from the floor of a 10 by 13 room, with all doors and windows closed to prevmnt air currents. The tempera- ture in the room was maintained at approximately 29° C. (84° F.) throughout the melting period. The bricks of ice cream were placed on the screen, approximately 6 inches apart. Each brick was placed on a piece of card- board, the exmct shape of the brick, in order to prevent the melting due to the weight of the brick.snd its pressure on the screen. A nail was punched through the cardboard into the center of the brick to hold the brick in place. 36 Observations of the melting bricks were made from time to time, and the exact time taken for each brick to melt was recorded. This test is especially valuable as a check on the relation of viscosity to quality in ice cream. Since the chief property of a good icstcream, from the standpoint of body and texture, is to be firm and re- sist melting, the different ice creams could be rated exactly by the time it took the bricks to melt down. The seventeen mixes of ice cream.were prepared six times. Results were taken of the melting and scoring each time. The melting ice cream bricks of the~ fourth, fifth, and sixth batches were photographed approximately two hours after their exposure in the incubation room. These photographs illustrate both the differences in time and type of melting. Part II leatin Quality Determinations In order to compare the most common.methods of testing gelatin with the melting test, a series of gelatin tests or quality determinations were conducted. the results of the melting test were taken as showing ihioh gelatin performed its function best in the ice cream. It was used as the basis of comparison for all the other tests employed. 37 The viscosities of the gelatin solutions were determined by the use of the HoJonnier - Doolittle Viscosimeter. This instrument is a modification of the torsion viscosimeter devised by Doolittle in 1893. A metal sphere, fastened to a dial, is suspended by a wire. about twenty-five inches long, from the top of a goose neck support which extends from the base of the instru- ment. The wire fastens into a knurled nut at the top. The metal sphere is lowered into the liquid to be tested until it is completely covered. The dial is then turned clockwise through one revolution, stopping with the zero degree in line with.the pointer. The dial is held in . place by means of a lug and trip. lhen ready to make the determination, the trip is released. ‘Due to the torque on the wire, the cylinder will revolve back to the zero point and continue in the same direction a certain distance, dependent on the viscosity of the liquid. The degree at thich the dial stops represents the viscosity of the sample, expressed in degrees of retardation. Since temperature exerts a large influence upon viscosity, the solutions to be tested must be accurately standardised as to temperature. The solutions tested were made up to a definite concentration, placed in a refrigerator at 35° F. and left there over night. They were withdrawn early the following day, adjusted to 70° F., and tested. Different concentrations of the gelatins were tried, in order to determine which gave the best results. 58 It was found that 0.76% solutions at 70° F. gave very good results, and the data presented on viscosities was obtained at this concentration and temperature. Jelly Strength. Investigators agree quite generally that the Jelly strength test isthe most accurate method of testing gelatin for quality. These gelatins were tested by means of a Hall Jelly Strength Tester. This tester, (Figure I) is a very simple device and it no doubt gives as good results as any other tester on the market. There would appear to be some features of this tester which are quite undesirable. The dial on the scale has only four main divisions, each having ten sub- divisions. This gives a total of forty possible value- tions for the gelatins. It was found that in the seven- teen gelatin samples examined, the variation ranged from 1.8 to 2.8, a difference of sixteen marks on the scale. This gives too many of the medium gelatins the same value, or practically the same value, so that there is no differentiation between their qualities. If the scale were made 1arger,so that values which are identical as read on the present scale could be distinguished between, the apparatus would.be more valuable. Regardless of’how carefully the Jelly strength test is made, it is practical- ly impossible to get identical duplicate results. This makes the apparatus undesirable for scientific purposes. A - Plunger B - Junction of Plunger and Gelatin - Gelatin - Knurled Handle - Lever Recording Hand Screw Block - Scale HmOWt-IJUQ l Glass Hall Jelly Strength Tester. Figure I. 39 There is also considerable tendency for friction in the working parts, so special care must be taken that it is well lubricated at all times. The Jelly strength test, as employed, was divided into three operations: first, putting the gelatin samples into solutinn; second, cooling the solution overnight; and third, testing the Jelly. In putting the gelatin into solution, a sample was first taken from different portions of the container. This was thoroughly mixed and 7.1 grams accurately weighed out. Beakers were included in the equipment which have an etched line around them. ‘1 beaker was filled with cold water up to the line after which the 7.1 grams of gelatin was added. The beaker is so graduated that this produces a ratio of 1 part gelatin to 33 parts of water. The mixture was allowed to stand for fifteen minutes, in order that the gelatin might settle and swell, a water bath was heated to 140 to 1500 F. and the soaked gelatin placed in it. The gelatin soon went into solution. The beaker was removed from the water bath and placed in a three gallon ice cream can. This can was placed in an , ice cream tub or packer and the tub filled with crushed ice (without salt) in order that a temperature of 40° 1. 4might be maintained. The beaker was left in.the ice can over night - approximately fourteen.hours in this experi- ment - and then taken out and tested immediately. 40 To make the strength determination, the tester is placed upon the beaker. Care must be taken.that the screw block rests upon.the top of the lever, so that the recording hand rests exactly at the zero mark. The plunger is now lowered until the bottom Joint Just clears the gelatin surface. This can be accomplished best by lowering the plunger until its shadow Just meets the gelatin. The depression reading is secured by turning the lever, thus disengaging the plunger which allows it to fall by gravity onto the Jelly. The Jelly strength is read directly on the scale, the value being at that point where the top of the recording hand rests on the dial. The Jelly strengths of all the gelatin.samples were run in duplicate. The value of each sample was taken three times and the average of the three figures as the value. Acidity Test. Since the statement is so commonly made that acidity in gelatin is undesirable, it was deemed wise to determine the acidities of the different gelatins in order to learn what relationship exists be- tween acidity and quality. d.modification of the Mann's Acid Test was used to determine the acidities. This test is based on the principle of neutralizing the acid present with n/io sodium hydroxide, using phenolphthalein as an indicator. 41 The acid present in the gelatin is considered to be equivalent to a like amount of hydrochloric acid. The percent of acid in the gelatins was computed by the following formula: c.c. HZlO HaOH used x .00355 x 100 equals the percent gram go a 11 use said. In making the determinations, one gram of gelatin was weighed out and added to 15 cc. cold water. The gela- tin was permitted to soak for approximately five minutes after which it was dissolved in a water bath at 150° F. Three drops of phenolphthalein solution were then added and 11/10 sodium hydroxide was dropped in from a burette, until a faint pint color, which persisted for a minute , was obts ined. This was taken as the neutral point and the number of cubic centimeters of sodium hydroxide re- quired to produce this color was used in making the cal- _ oulation to determine the percent of acidity. Two acidity determinations of each gelatin were made. Clarity, Color, and Odor. Ihen the gelatin solu- tions were heated to approximately 150° P., immediately before the acidity determinations were made, observations were made of the clarity, color, md odor of the solutions. The object in view was to find if any relationship existed between these factors and quality in gelatin. The results of these observations are presented in tabular form in the "Results" section of this paper. 43 Bacterial Counts. In order to determine to what extent the gelatins were contaminated with bacteria and how much each would contaminate the ice cream, bacterial counts were made of each gelatin sample. These counts were made by members of the Bacteriology Department, Michigan State College. IMilk.powder agar and standard agar were used as media. In making these analyses, one gram of the gelatin was weighed into a sterile dilution flask. Sterile saline solution was added to the dilution flask until the desired dilution was obtained. The gelatin was then melted.in.a water bath at about 50° C. After it was melted, the flask was thoroughly shaken and one cubic centimeter portions were immediately plated on standard nutrient agar and milk powder agar. The plates were incubated at room temperature and counted at the end of forty-eight hours. The counts represent an average of two plates, unless otherwise noted. lermentatioanest. The presence of liquifying and gas producing organisms in the gelatin samples was determined by the fermentation test. To each of’a series of sterile test tubes, 10 cubic centimeters of sterile water was added. Samples of the gelatins were carefully taken to avoid contamination, and 0.5 of a gram was added to each tube. The gelatins were thoroughly shaken up, allowed to swell for approximately 10 minutes, and were then dissolved by placing the tubes in a water bath 43 at 150° F. The tubes were then placed in the refrigerator at 35° F. for three hours, so that the gelatins might thoroughly Jell. They were then exposed at room tempera- ture - approximately 70° F. - for six days, in order to determine which gelatins contained liquifiere and gas: producers. This test*was made in duplicate. Price. Although price is not a recognised index of quality in gelatin, it is quite often customary to purchase gelatin on the basis of price alone. Conseguently, the prices of the different gelatin samples are quoted and a curve made to compare with the curve prepared from the results of the melting test}. 44 RESULTS and DISCUSSION Part I - Freezing Experiment Melting Test The time required for the ice cream bricks to melt at a standard temperature is presented in Table No. I. The melting time for each of’the seventeen bricks in the six different batches is given in hours and minutes. The average melting period of the ice cream samples stabilized with a particular gelatin in the six determinations is also given. Due to an error, the results of numbers 6, 10, and 14, were not secured in batch No. I. In batch No. V, there was an unaccountable discrepancy in the time of melting of number 13, as compared with its melting time in the other batches. Considerable difference was noted in the way different samples melted. Those ice creams containing gel- atin which were not especially resistant to heat, as samples Nos. 2, 3, 8, 9, 11, 12, 14, and 17 usually started to melt quite soon after exposure. The melted part ran down the sides and through the screen. They'melted very much like frozen.milk, in that the melted portion was liquid in nature. Numbers 1, 4, 5, 7, l5, and 16 did not melt so quickly and the melting was of a different nature. The 4.5 mm 3 m mm mm mm mm 9 mm 5 an om mm nun MMd’d‘KOd‘MMLndmd : anom omoamhw mm 0: mi repose: udom mmpncam anew H> m: n diiidh'dzfmmimm O m b taxed-mm mmmd‘md‘d‘ : mm mm m 0 p352 930m >H mmg-rekommmmrrd-m : em on on in ma m m an om ma 2 we mm mm m m puma: Hdom HHH Mnnfidz xdm newsman one mnsom ma vommmmxm H MMdithM:MM-fl' m 00 on mm om mopnfln neon HH d‘MMiM01MMjnmm 2.. cm. me mm 0: mm mm mm S 8 0 mouse“: usom H exofiam smoao eOH no mcdpaom eoz mamxa :fimm n: OHNM HHHH amnimxoh-soox napmamo no 909852 mm am am Gd: Ham 0034,33 “flow 46 n m omens». S on. em H> :rm: mm me 2 R no 2.5.3 know > m s m 1 mm mm 9i R moaned: meow wanna”: know commandos I H >H m r m H mm an ON mm iLHHH kneadz NH: .02 mgm I . _ . . 1...-.. _ _. . IIA ._ v ,.I:I#.. .. _ ..T III... _ . , va . . .0 c . _ . . I _... . ...... . _ u . .... II. I'll. I all ll.e+IlIIII aII-Ircli.-.lla - ._ . . . I..... I H. . . . .I d. a' I"|-D.‘III HHHaqemHH H5.55H55H5m 5. HHH_55555 .- . 'III I ...I '1' I 1" . -.555u 55HHHmH 5H 555H55H55 5H55H55 H5 a I IIII‘I 1"." Ian- I II I III I- III I u _. . o . u u a . . 5 _. .o - e _ n a n . .a n . . 0H. - n . _— _ _ I . . .— .. I a I all _ .. 5 . ... u 5 u _ p .«l .- ._ _ . __ H 5 . - .1 _ . . I U I. U I - _ u , .I I I I I- .. I II I I. . I _ _ _ n .. _ . . . I e _ A . I I _ _ . . I I n H . m . . I A. . . I o a H I I e I I I. I e . I I _ . I I I O C I . u . .. . I _ ...H . I a . . 9. I _ v V I I ._ . I I I v -..I} I II _ _ I . nil II I u u. H o ., v v I - v. . e v a . a o I.. v . _ I I . _ _ . . _ i 0 a _ A _- . I h _ . _- u I.. u‘I'J . _ I . .. I . I.|| .l I. I. I . I I I III I IIIIIU I I . I. . . II a 5 u I _ H . . n u w n _ u 1 t - I 0.. a _ - .. v - e _ e. I .. . . m .. . . 5 e» . . I . . . . _ v o a I. v“. 7 J! .1 _I . II I r . ._ e . ._ . :VII «_ . ee 5 _ c m; «WdIII II . _. . H I _ . _ . ._ I. I H; . . ‘1 ..I .I I I a I I III I- I .I..II t OIII 1| I ”IJ.II..IHI.‘ _... _. ....I .._ _ _. .... II .u._ . ,Houvl .. . . .e n _ a a _ .. e elf. _. _. I I.. _ . . _ I .Ie. _. e 1 _II WI ._ e0 ‘0,“ Y. a e - ... I , 1.1L 5 I .I L .. _ . .. I c...AI It _ . I O I . 2 L . _ I . 1.. _ . 1H . I I I.. v 1 < I I _.. A I . u . . _ . .. - . . . e w; _ Q _ _ .5. H. .._ . . . t. .. .I 4 _ _ . .. H ”I as. I .lu I I a It I 5.. . Ill'elll __ . _ . . _.. . +Ielel - _I . I e H . . I I4. '7 I. L - I _ . _. .EUDOHH _..e r . . . . . . . H .II o I . . . u u _ . .c 1 . .01 L. ._ . I I . - I I . . ... . .. . _ .. . . . . , .. _. . ,. ._ .. . H ... I. m. .. .II. A .. .e. 64.... . . .. I _ II I. _ ._ -I I I. I e al .. Tl _ II . IL .II- ell-r 5-..! I . IIII . . J . .I: .,. . _ .. _ _ _ _ . . . . 0“. L I .. I . I . I ... . e , a_ I .. a . - u . .I ._ H II. +._ 5.. .. "”0 . . . . . .. . _ ...... _ . H .fiI : . . r * v a O. . v .0 . u . I I. . . .. e. l _ _II.. I . _ H ,5 . . .. I. ..IwHwI . _ 0| _ I I I a II . . ___- ...I_.. II .. ._7 ...I} .. ... _ .. ,_ 1w . _ . I a . . l e . .. I. . . . ,. .. H .5 I . _. L . I. _ I _. U ‘. en _. _ fl; . _ I. . _ _ 9 .5I ._I. e I we ”4 n _ o . I. . _ .. . ... .... - H _ . . . , _ r . . .. .4 . 1 : I e . . _. , I we _ . _ . e.‘ .0... i .I .._. .. . .. . I. .,I ll _ . _ ...I _ . Y-ITIII _lA ..Ia-...II ..InI ..I I _ _I.l.- ._ I II we! H5.I..ILI.IaI.IlI. .... I .I . . . . I I. . . .. . ILIHIA __ __ . . _ . . _ _ .. ..gmL _. _ . _ H u I _ e I O I _I _ _ . ._ _ . _n _ . a .1 u u .. . . a . _ . . ., I.- _... b _ _ _ _ _ . I _ e . . I H H . .4. . . I I II. I II N . v. _ . 2.55%.... O I II . I. Is a 1 _ . I I I I.. I _L I. H . .I . I _ A I ”LIL. . "A1 e .. I I. I. . . . L IF. .... . I - _ a. ., I. _... _ . .. .a._ . . e _- _ e ..I a ... I _. I. e a I . a. o o_ __e . .... I . . I..... c. I . I _ . I LIfI . fit.” a _ . . .. .n I .41.... e .IA .‘ a . II "III I 'l' I .P _ II|PIF. '1 Et.L D‘PARTN ENT 0' MA'I’HEHAT'I'." encountered in getting the results to check. If a sufficient number of tests are made on the gelatin and the averages made. this test should give results which are quite confirmatory of quality. Jelll-Strength and melting Test The results of the Jelly-strength test are given in Table VII. These determinations were made in duplicate, and check very closely in most instances, as may readily be seen from the table. However, there are in some cases wide variations between the two results. The inability to secure checks with this apparatus seems to be its greatest limiting factor. A thick skin often forms on top of the gelatin to be tested. and this, no doubt, often influences the reading somewhat. Graph IV shove the curves plotted from the average values obtained by this test, as compared with the value! obtained by the melting test. These curves are practically the same, having only two slight discrepancies, indicating that considerable correlation exists between the two tests. The correlation coefficient between Jelly Strength and the Melting Test is -O.683 :I: 0.046. This value ie 12.9o time! the probable error, indicating that the odds are infinite that if the experiment were repeated; the re- sults would be -O.563 i: 0.045. The correlation, in this 65 instance, is negative due to the way the Jelly strength values are read on the Hall Jelly Strength Tester. On this tester, the higher the duality of gelatin, the lower the value. A negative cwrrelation is Just as significant as a positive correlation, and it therefore carries the same value as though it were 0.583 t 0.045. This proves that a very strong correlation exists between Melting Time and Jelly Strength. This latter test may consequently be used as an indication of quality in a gelatin. Acidity and Melting 23st As is indicated by Table VIII, the acidities of the seventeen different gelatins ranged from neutral to 1.15 percent acidity. Taking the latter sample as a basis for calculation and using the usual amount of gelatin, 0.5 per cent, in the mix, it is apparent that the use of this gelatin would only increase the acidity of the ice cream mix by the following amount: 1.15 x 0.005 : 0.00575 per cent acidity. Since as much as 0.35 per cent acidity is often developed in the ice cream mix without any disastrous results, it is apparent that the amount added by this gelafln is negligible. It is possible that other commercial gelatins have a consider- ably higher acidity than those used in this study, but it is not likely that they will have a sufficiently high acid con- tent to imperil the ice cream. The only possibility of undesirable results from 66 TABLE N0. VII Jelly Strengths Number 1'1 rst Second gglatin. Determination; Determination Average 1 1.9 ' 1.9 1.9 2 2.2 2.2 2.2 3 2.0 2.0 2.0 4 1.8 2.1 ' 1.95 5 1.7 2.0 1.85 5 1.2 ' 1.4 1.5 7 1.8 1.9 1.85 e 1.9 2.1 2.0 9 2.8 2.8 2.8 10 1.4 1.4 1.4 11' 1.9 1.9 1.9 12 1.8 _ 1.8 1.8 15 1.5 1.8 1.7 14 2.5 2.2 2.55 15 2.1 2.2 2.15 15 1.8 1.8 1.8 17 2.2 2.5 2.25 MICHIL-AN AGR'CULTURAL (”.IIJ E"! I I I I I I I I .I J I I II! I! III] .' ‘II-'IC 'I ._ . o .. .. . I I a I I l . I 0 I e ... . _ o I _ .I u I a e ..a as e. n ..I. . I .L . . . _. . . . I we I I . ..... I _. _ .. _ . _ . _ _.... ._ . . II _ . . I I _ I... . .... .. . _...--.._. . ..H._ V In. .....7 .._nmma wflaafiofie: .. 6 . . ... ... _.... . _....-. .__._ . : . . i I I . I I. a h .. . e . _. _ _. ”er... . I“ I L I.. I . I . I . I . . I I _ u . .._ .... _ o . - I . I . - I _ . . n. . I I . o I sdI . I . I I I.. . I I a . .1. A . _ I I U u- _. _. _. I .I. l l I I _ II I - — as 5 y - p. - . .e ._ . e . ..A I. f _ . a a I. Ievz .s ._rn_ , .I II I I. _ ,.<._ J I. 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II _ I ee. ___ . . .. . .. . . . _ -. - . ... ._ I .. . . . _ I I . o. .. .fl ' 9. II T . I c. I. _- I. _ a I I . .o a — . p v. I". _a. . _ __. I . I. .a _ . I .. a . . . a. . s ... I. 9- a I I I ._I .. e I , - o — w . a-I .a-‘L—u_ . .. _ I II . . a I I I .. _ .._ - I .l ,. _, n . w . _ I "..r. . III...-._ . a . _... .a _.e .. «__nl. . «no. - ___. . 1-I. . I... __. .....I I .Ie ._ [.I.-ll. 'II- I I leIIIIlaI I I I--! .-.I-r... r I I blIIIL-III I..-III .II III' :I I. ’l..|. s I. H I.III _ o _- I _ O _ _ . U V _ . . . o. __ II _ . I. I _ I . _II .. h _ - _ I ea I l, ... _ . . I _ III _ I I - I . a . . I _ - .. I .— Iv l I l I I. I I I _ - II I _I IV _ _ v I, . .. — . . ...I..... I . . _ I I. I__ l I_ . .In I . . 0 II _ q - I I J— r ..H I.. L —_ __.I .. . n. .. . . .I | a. I. I _. A -III.. III - .. I — _ I I y l I. x .. _ o . _. u I h C _. I II I ..- . --. z - «.1 d I h _ I OI m I . 0 II . I. 1. _I I. _ _ . _ 'I.‘ I I 1 . -.. . I _ . _ . ~.._ (I .I.... I I a I.- r I. I_ .I.. . _ _. _ vI .I. .I. II II I... f , ._ I ._ I. . II . . L .H . . m _— __ . ._ I . o .. _ _ h . . . . _ ._ I I I . I I ._ . t In . . __ II I I. _ e.I e I .0 .II. . . _.. _ “1‘ ._ I u.. _..“. ... '1‘ 0 . _ .W. . be . .. _ ._ C - fl . ___ ...... . I III I.I.IIIr.H . .... .... _ _ _.e.~..._ L . I. .U .1“ .. I I_ a _l ..I _ ._ L_. . _ e.I_. Ir ._ ... ._ .. . ...ugfx- :I. . I 6.: L I. II'IIIIIIIII-II ,IllaIIII Ins-III u I..- v. I . I I ... a Q I _ I. . .... j.- e _— _ I r. _ I 1 _ e .I . x v.1 . Let. .1.» ._v _ . I. I fI * m . Iv . . a _. _ IO. .. 0 II .I.. .I.; _ ._I _ . I __.. I. . w ._ 4 I I I I; III a ...I III .... ,. . II a. u . . _...: .- .- ...I IV. - .... ...e I v _. n e. 1.IIA - II ,e.Ie.. _I I .. «II-an... a L _.. I. I _ u .- .- [I If. .I- I I. _ I I . . 1. . I.. I? II . . .. . a H. . _ IIII sllrlsPe-Illllll'llrt'lrw DEPARTMENT OF HATHEHATIL - 68 TABLE N0. VIII Gelatin Aciditiéa Number First Second gglatin Determination Determination Averago 1 0.44 0.44 > 0.44 2 neutral neutral neutral 3 0.80 0.76 ~0.78 4 1.02 1.06 1.04 6 0.73 0.77 0.76 6 0.91 0.91 0.91 7 0.20’ 0.20 0.25 8 0.29 0.29 0.29 9 0.29 0.29 0.29 10 1.13 1.17 1.16 11 0.16 0.16 0.16 12 0.37 0.37 0.37 13 0.77 0.73 0.76 14 0.16 0.16 0.16 16 0.73 0.73 0.73 16 0.68 0.68 0.68 17 0.18 0.18 0.18 69 away mqufio: mpfiuflod .wwoa mnflpflo: op hpfiufio< nfiaaflow no mafipuaom 3* b undue no n.o 010 «.0 w.H 70 the use of high acid gelatin.wculd occur When a small amont of milk, -either skim or whole, is used in dissolving the gelatin. When this method of dissolving the gelatin is practiced, the mixture of milk and gelatin is quite concen- trated, and the acidity present in the gelatin may be sufficient to curdle the milk. The danger is enhanced when the acidity of the milk is already high. However, when.the 'gelatin is added dry to the entire mix, or is dissolved in a small amount of water and is then added to the mix, there is no danger of curdling. Graph V, which compares the acidity curve with.the .melting test curve of the different gelatins indicates that little correlation exists between the two tests. However, When the mathematical test is applied, we find that this is erroneous. The correlation coefficient between the two tests is O.593.t.0.044. It has a value of 13.48 times the probable error, showing that the odds are infinite. If the work were repeated, the value of the correlation would be 0.593 t 0.044, making the correlation between the two tests very significant. From.this we may conclude that, though high acidity itself is not to be desired in gelatin, it is associated with high quality. Clarity, Color and Odor The clarity, color, and odor of the solutions of 71 the gelatin samples are given ianable IX. A study of these results indicates that no relationship exists between these three factors and quality, as determined by the melting test. These factors are too easily affected and controlled by the process of manufacture to be good indices of quality. Bacterial Counts and Fermentation Test The bacterial counts of the gelatin samples are given.in.Table.X. The counts made on Standard Agar lo. I. and Milk Powder Agar No. I, were made six months before those which are marked.Nc. II. They were probably con- taminated during this time, which accounts for the higher count on the later date. It will be noted that the results or the bacterial counts compare quite favorably with those of the fermen- tation test as given.in Table XI. Gas producing or liqui- iying bacteria might be suspected in those samples contain- ing the largest numbers of organisms. Such.was the case with two exceptions, numbers 3 and 13, which had relatively high counts but did not show the presence of liquifiers or. gas producers. Price and Melting Test Table XII and Graph VI shcwthe price of the gelatins and the relation of price to quality as determined by the melting test. In the samea 1 to 7 and 14 to 17, the curves 4 s..—. n Number of Gelat in 1 ‘:c a: -a oz cm e. as to r4 as h‘ we hlvlfl hi ii -a a» c: e» Il°t0 Id 40 TABLE N0. IX Clarity, Color, and Odor Clarity slightly cloudy w w clear w w a w cloudy clear cloudy clear I. slightly cloudy n I! 010E! 9.0.1.05 white amber light amber white w e :0 light yellow amber white light amber white 72 Odor strong very strong tankage good slightly strong good w slightly pig ' strong ' pie . good w slightly strong good strong slightly strong 73 TABLE NO. X Bacterial Counts Number of Standard Agar Milk Powder Agar Gelatin M No. II No. I No. I} l 150 550 60 200 a 1.200 136 .000 300 - 3 50 5,250 100 1,200 4 50 8 50 100 5 60 276 50 - 6 100 500 150 50 7 1,750 4,850 - 3.500 s 150 180,000 250 166,000 9 50 176 60 - 10 50 350 50 - 11 100 150 50 - 12 100 300 160 - 13 50 20,000 150 60,000 14 100 300 100 200 15 50 - 50 - 16 50 - 50 - 17 - 150 150 50 74 TABLE N0. XI Fermentation Test Number of First Second Gelatin Determination. Determination 1 ‘ _ - a 2 a - + 3 - - 4 - - 5 - - 6 + - 7 e - 8 + + 9 - - 10 - - 11 - - 12 - - 13 - - ...I ' IF + ... 15 - - 16 - - 17 - - * The plus sign indicates the presence of liquifying or gas producing bacteria; the minus sign indicates that no gas or liquifaction was produced. TABLE NO. XII Price or Gelatins Number of Gelatin 1 W'QN‘IO‘U‘PNN r4 Id b' +4 be P‘ .s o. Ol'fib ca 53 I: .o Price (cents) as 55 50 50 55 70 50 50 60 so 57 75 65 50 e0 65 42 75 ease msaaasn 76 sneefloo.uo eeaam .pmoa maupaofi on» be. 603233 .3 seasons on cheeses no sense do nonsense H» gases or on 00 0h 0m 77 would lead to the belief that considerable relationship exists between price and quality gelatin, but with the other five samples, there seems to be no relatinnship whatsoever. However, that there is considerable rela- tion between the two is proven by the calculated corre- lation coefficient. The correlation between price and melting test is 0.311 if 0.060. Thus, the correlation has a value of 5.18 times the probable error, which in- dicates that the odds are 1400 to 1 that if the work were repeated, the correlation would be 0.311.t: 0.060. The relationship between the two factors is very signi- ficent, so we can conclude that price and.quality bear considerable correlation. Comparison of Tests Table XIII gives a mathematical comparison of the important tests discussed with the melting test. These tests are listed, from top to bottom, in the order of their correlations. The first three tests listed, Viscosity of Gelatin Solutions, Acidity, and Jelly Strength tests, have very high correlations. These correlations are so much greater than their probable error that the odds are infinite thatwere the work repeated, the correlation would fall within the same limits of error. Since the Score correlation was the smallest of'the lot, it was taken to be basic. A survey of the three highest valued correlations shows that their Differences (the correlations minus the 78 correlation of the base) are greater than their Probable Errors of the Differences, so that the differences in value of these correlations and that of the base are quite significant. The three tests showing the lowest correlations with the melting Test, Price, Viscosity of Mix, and Score, are so similar in value that there is little difference. Both Price and Score show greater Odds than does Viscosity of Mix, due to the high Probable Error of this later test, but the *robable Error of the Difference of both Price and Viscosity of Mixes is greater than the Difference. The . difference in value of these latter three tests is less than the Brobable Error, showing that the differences are not significant. 79 9.5.0 enema -.....i seem a » on." oo... 80.0 :02. 03.0 a " mm aim 80.0 200.0 33: 3.33009; ammo. Hm0.0 a ” 003a 0H.m 000.0 Han.0 cases 02.0. numé . 00.0” 940.0 numéa newseaem has. n30. 900 . . 3.3 30.0 30.0 32:04 ammo. 03.0 .352” SA ... 10.0 01.0 .8338 usages no 3.38.: 23.3. 0938 33.3.33 no 3333.33 «0.33 330.8 henna 2033908 eomonouuan ammo e noapeaonuoo eanwnonm medpeaounoo henna eansnoum 3.009 no mouananaoo 30333:: HHHN .on nqmdh 80 Summary and Conclusions The melting time of the ice cream bricks proved to be a very good index of quality. Little correlation exists between the scores of the ice cream samples and the melting test. The human element undoubtedly enters in too much to make scoring an accurate test for quality. The work done on the viscosities of the mixes tended to show that viscosity, as a measurement of quality in ice cream, is practically valueless. Viscosity as a measurement of quality in gelatins compared very favorably with the melting test, indi- cating that as a test for quality, viscosity of the gelatin solution can well be adopted. The Jelly-strength test gave results comparable to those secured by the melting test. The acidity of the gelatin samples was insufficient to endanger the ice cream mix. A high positive correlation exists between acidity and quality in gelatin. Clarity, color, and odor showed no relationship to quality. The gelatins contining gas-producing and liquifying organisms as determined by the fermentation test, were 81 with two exceptions, found to be among those with the highest bacterial counts. 9 A high correlation exists between price of gelatin and quality. 82 BIBLIOGRAPHY Getman, F.H. Outlines of Theoretical Chemistry, vol. 5, p. 80.. Hatschek, Emil. An Introduction to the Physics and Chemistry of Cellpid£.p. 21. menhart, V.H. Relative influence of three gelatins upon viscosity of ice cream. Ice cream Review, July, 1923; pp. 8, 106. Zoller, 3.3. Cited in Bogue's "Colloidal Behavior", vol. 2, pp. 804-805. ‘ Mortensen, M5 mechanism of overrun in the manufacture of ice cream. Creamery and.Milk Plant Monthly, vol. 3, no. 9 (1915), pp. 31, 22. Clayton, Colloid problems in dairy chemistry. Second Report on Colloid Chemistry and its General Indus- trial Applications, British Association for the Advancement of Science,(1919), p. 116; quoted by Palmer, L. 3., "The chsnistry of milk and dairy products viewed from a colloidal standpoint", Journal of Industrial and Engineering Chemistry, vol. 16, No. 6, p. 634. Parfitt, 3.3. Study of gelatin for manufacture of ice cream. Ice Cream Review, (Aug., 1923) p. 58,60; 76,78. ' . Alexander, Jerome, and Bullowa, Jesse, G.M. The influence of colloidal protection on milk. Jour. of 10 11 12 13 14 15 16 17 18 19 85 Am. med. Association, 55 (1910) p. 1196. Alexander, Jerome, and Bullowa, Jesse, G.m. The influence of colloidal protection on milk. Jour. of Am. med. Associaticn, 55 (1910) p. 1196. Dcwney, T. B. The food vflfiue of edible gelatin in ice cream. Ice Cream Trade Jour., (May, 1923) pp. 55,57. Downey, T. B. Edible Gelatin in ice cream. Ice Cream Review, vol. 7, no. 9, (April, 1924) pp. 106-108. Bogus, R. H. The Chemistry and Technology of Gelatin and Glue, p. 561. 'Masurovsky, B. I. Newer knowledge of the use of gelatin in ice cream. Ice Cream Trade Journal, vol. 20, no. 3 (1924), pp. 81-82. . ' Zoller, H. 3., and Williams, 0. E. Sandy crystals in ice cream; their separet ion and identification. Joure Agr. 388., 21 (1921) p. 791. Lucas, P.S. Personal interview. Burke, 8. D. Quality gelatin. Ice Cream Review, vol. 6, no. 10 (1923). pp. 44-48. Hall, T., and Houtz, R. L. Testing gelatin for use in the ice cream mix. Ice Cream Trade Journal, vol. 19, no. 6, (1923), pp. 55-57. Williams, 0. E. Why gelatin is required and its effect on quality. IMilk Dealer,, vol. 6, no. 5 (1917), pp. 18-21. Hanhart, V. H. Relative influence of three gelatins upon viscosity of ice cream. Ice Cream Review, (July, 20 21 22 23 24 25 26 27 28 29 84 1925) pp. 8; 106. Turnbo', G. D. The effect of gelatin on the texture of ice cream. Ice creamRevieI, (June, 1922) pp. 108-118. Parfitt, E. H. Some factors influencing quality in gelatin and the use of the fermentation test as an index of bacterial contamination. Jour. of Dairy Science, 6:278-282 (July, 1925). ' Bogus, R. H. The Chemistry and Technology of Gelatin and Glue, pp. 269-423. Alexander, Jerome. Glass and Gelatins, pp. 189-190. Smith, C. R. Determinations of the jellying power of gelatins and glues by the polariscope. Jour. of Ind. and Eng. Chem., (Sept. 1920) p. 878-881. Hall, 7., and Houtz, R. L. A Jelly strength test for judging edible gelatin. Ice Cream Trade Jour., vol. 19, no. 7, p.63-64. I Smith, E. s. U. 5. Patents no. 911, 277 (1919) Cited by Bogus, R.H., "The Chemistry and Technology of Gelatin and Glues", p. 375. Sheppard, Sweet and Scott. The jelly strength of gelatins and glues. Jour. of Ind. and Eng. Chem. 12, no. 10, pp. 1117-1011. Alexander, Jerome. Proteins. Cited by sheppard, Sweet and Scott. ."The Jelly strength of gelatins and glues", Jour. of Ind. and Eng. Chem. 12, no. 10, p. 1007-1011. Alexander, Jerome. U. 8. Patents no. 882, 731. Cited by Bogus, "The Chemistry and Technology of Gelatin and Glue", p. 374. 30 32 33 35 36 37 38 59 4O 85 Garrett. Philadelphia Magazine, vol. 6, no. 6, p. 374. Cited by Bogus, "The Chemistry and Technology of Gelatin and Glue", p. 394. Bogus, R. H. The structure of elastic gels. Jour. of Am. Chem. Soc., vol. 44, no. 6, pp. 1343-1356. Loeb, Jacques. Amphoteric colloids. Jour. of Gen. Physio., vol. 1, pp. 59; 257; 555; 485; 559. Burke, A. D. Gelatin, the good and bad. Ice Cream Review, vol. 6, no. 8, p. 78-82., Lucas, P. S. Unpublished data. Hnnziksr, 0. F. The butter Industry, pp. 597-599. Bogus, R. H. The Chemistry and Technology of Gelatin and Glue, p. 401. Ellenbsrger, H. B. A study of bacteria in ice cream during storage. Cornell memoir no. 18. Hammer, B. w. Bacteria and Ice Qream. Iowa Bulletin no. 134. Ayers, H., and Johnson, W. T. A bacteriological study of retail ice cream. U. 3. D. A. Bulletin no. 303. Gordon, J., Prescott, 5. G., Heinemann, P. G., and Pease, H. D. The bacteriology of ice cream. Report of experi- ments referred to at hearings on ice cream before Dr. C. L. Alsburg at Washington. National Association of Ice Cream7Msnufscturers, 1914. Cited by Ellenberger, H. 3.. Cornell Memoir 18. 86 41 Gordon, J., Ice Cream Trade Journal (Jan. 1912) p. 33. Cited by Hammer, B. W. "Bacteria and Ice Cream", Iowa Bulletin no. 134, p. 286. 42 Parfitt, E. H. Study of gelatin for manufacture of ice cream. Ice Cream Review, vol. 7, no. 1, (1923) p. 58; 60; 76. 43 Brannon, J. M3 and Tracy, P. H. Gelatin as a source of bacteria in ice cream. Jour. of Dairy Science, vol. 8, no. 2, pp. 115-127. 87 Appendix Table No. I. Number of Gelatin £53111 1 United Chemical Company 2 Chalmers 3 Atlantic 4 Swifts 3A 5 Swifts 4A 5 Swifts ea 7 Duche 8 united States 9 Crandsll Pettee 10 Grayslake 11 Whitten 12 Crystal 13 Dunne 14 NHlligan and Higgins 15 Delft Imperial 16 Delft Supreme 17 Essex "1711111171!11111111115