THE EFFECT OF VISCOLIZATION ON SOME OF THE PHYSICAL PROPERTIES OF MILK THESIS FOR THE DEGREE OF M. S. Charles Patrick Halloran 1932 .. . ..A r 1. .1. .2 “a THE EFFECT OF VISCOLIZATION ON SOME OF TEE PHYSICAL PROPERTIES OF MILK TEE EFFECT OF VISCOLIZATION ON SOME OF THE PHYSICAL PROPERTIES OF MILK Thesis Respectfully submitted to the Graduate SChool of Michigan State College of Agriculture and Applied Science in partial fulfillment of the requirements for the degree of Master of Science. By Charles Patrick Halloran “I.— ' 1952 r» I THESIS ACKNOWLEDGMENTS _ & The writer wishes to express his sincere appreciation to G. Malcolm Trout, Assistant Professor of Dairy Manufactures, for his kindly advice and guidance in carrying out this work, and for his aid and criticism in the preparation of this manuscript. The writer also wishes to thank E. L. Anthony, Professor of Dainy Husbandry, and P. S. Lucas, Associate Professor of Dairy Husbandry, for their cooperation in making this work possible. 96499 TABLE OF CONTENTS INTRODUCTION REVIEW OF LITERATURE 1. 2. 5. 4. 5. 6. 7. 8. 9. 10. ll. 12. 15. 14. 15. 16. 17. 18. 19. Extent of Viscolization Theory of Viscolization Effect of Viscolization on the Creaming of Milk "Viscolized" Milk Detection of the So Called Viscolized Milk Theory of Viscosity Effect of Viscolization on Viscosity Theory of Surface Tension Surface Tension Theory of Foaming Foaming of Milk Stability of Foams Effect of Viscolization on the Specific Gravity Fat Test of Viscolized Milk Stability of Proteins toward Alcohol . Size of Fat Globules Acidity of Viscolized Milk Flavor of Viscolized Milk Curd Tension of Viscolized Milk PURPOSE OF EXPERIMENT page 10 10 ll 15 15 17 18 21 22 22 25 24 25 26 27 28 PLAN OF EXPERIMENTAL WORK 1. 2. 5. RESULTS 1. 2. 5. 4. 4 5. 6. 7. 8. 9. 10. 11. Source of Milk Supply Experimental Methods Description of Tests Made Creaming of Viscolized Milk Viscosity of Viscolized Milk Surface Tension of Viscolized Milk Foaming of Viscolized Milk ' Stability of Proteins Titratable Acidity Babcock Test of Viscolized Milk Specific Gravity of Viscolized Milk Size of Fat Globules FlaVOr of Viscolized Milk Curd Tension of Viscolized Milk DISCUSSION CONCLUSIONS LITERATURE CITED page 29 29 29 5O 54 54 56 58 4O 42 44 46 49 49 52 55 59 65 67 INTRODUCTION For years the public has judged the quality of milk chiefly by the cream layer at the top of the milk bottle, reasoning perhaps that the deeper the cream layer on the milk the richer was the milk._ Such a de- ductionflhy the layman.is perfectly logical, especially when one realizes that the amount of cream which rises on a bottle of milk is the only standard by which the consumer may judge the richness, or fat content, of the milk. Unfortunately, this basis of measurement is not a reliable indication of the amount of butterfat present in the milk. \‘i’v A.bottle of milk showing a deep cream layer is not necessarily richer in fat than milk in which the cream layer is less pronounced. This fact was universally accepted by members of the dairy industry at the time of the adoption of the Babcock test to determine the fat content of milk and of cream. . 5’ Since the beginning of the market milk industry firms distributing milk and manufacturers of dairy equipment have concentrated their efforts upon the production of milk having a deep cream layer. Special dairy equip- ment has been devised in order to avoid adversely affecting the cream layer. Even.the milk bottle has been so constructed as to make the cream layer ap- pear as deep as possible. Much research has been conducted to determine the temperature that would destroy pathogenic bacteria and yet not reduce the cream layer. Q } The milk distributor has catered to this inaccurate method of judging milk quality on the assumption that "the consumer is always right", which ‘ assumption is only justified from a dollar and cents point of view. Instances have been cited in connection with children's homes, state institutions, restaurants, and even private homes in which the cream had been poured from the milk and the remaining serum had been given to the children. This is in Opposition to the doctrine broadcast by our health authorities who have been recommending to everyone that a quart of whole milk is‘needed by every growing child as well as every adult. It is here that homogenization, or viscolization, of milk finds the greatest argument in its favor. Furthermore, the introduction of the single service contain- er has minimized the importance of the cream line on milk. \q-} Viscolized or homogenized milk has been and is being processed with two different aims in view which are antagonistic to each other. One group went to the trouble of homogenizing cream and mixing it with milk of a low fat content to increase the volume of cream rising on the bottled milk. The use of this so called “Viscolized" milk promotes the common practice of using the top of the bottle of milk for coffee or cereal, thereby forc- ing the less fortunate members of the family to use the remaining portion which is little better than skim milk. -This process defeats the purpose of viscolization and renders the word a misnomer. The other group endorses the full meaning of the word homogenization, which renders the entire milk ‘ homogeneous and on which a cream layer does not form. I? Viscolization, or homogenization, of milk may be defined as the pass- ing of milk through exceedingly small openings at high pressure, as a result of which the fat globules are so finely divided that they are not affected ‘ by the force of gravity. Thus the fat remains evenly distributed through- out the milk. In view of the fact that considerable attention is being given to homogenization of milk, and that the effects of the process upon the physical and chemical properties of milk are not so generally understood, a study of viscolization, or homogenization, of milk as affecting these properties seemed desirable. REVIEW OF LITERATURE Egtent of Viscolizatigg Although the principle of viscolization is not new to the dairy in? dustry the process has not been used extensively in this country in COD? nection with market milk. However, in some countries the process has been accepted commercially. Jones (5) states that homogenization has been extensively used in the preparation of sterilized milk in Europe. This product is simply milk homogenized, bottled and then sterilized at high temperature. According to Jones (5), Hudson (50) and Hollingfiworth (4), Canada is the pioneer in the application of the homogenization prin- ciple to the market milk trade. The first successful commercial introduc— tion of homogenized milk took place at Ottawa, Ontario, Canada in 1927. At the present time, the homogenization of milk in Canada is mainly a product of Ontario, Quebec, and British Columbia, with a scattering of individual dealers in the other provinces. In the United States the homogenizer is used chiefly in the prepa— ration of sweet cream, ice cream, and condensed milk. However, in some Specific instance market milk, chocolate milk, commercial sour cream and milk used in manufacturing various kinds of cheese has also been homog- enized. Theory of;Yiscpliza=;g§ The homogenizer and the viscolizer, although somewhat different in construction, operate upon the same principle. They are essentially high pressure pumps which are capable of pumping under a pressure of 5,000 tn 5p LIP-2.. i.“ pounds per square inch and are so constructed that the liquid is forced .through a small opening known as the homogenizing valve. The pressure at which the liquid is homogenized is regulated by the closure of this valve. These machines are usually constructed in sets of three cylinders, each having a suction and a discharge valve. The discharge from the three cyl- inders is into a common manifold which leads to the homogenizing head. The valves are usually of the pocket type and may be ground using a common valve grinding compound. The homogenizing head consists of a hardened metal seat, against which a block of hardened metal, or composition materi- al is held by a spring. The pressure is regulated by the tension of the spring on the homogenization block. August Gaulin of France according to Turnbow and Raffetto (l) is given credit for this invention. Sommer (2) states that there are several views concerning the manner in which this fine dispersion of fat is accomplished by the homogenization process. According to one view, the dispersion results from the shattering effect produced when the liquid impinges against the side walls of the homogenizing valve. With-a clearance of 0.0001 inch in a homogenizing valve, it has been estimated that the liquid is traveling at a velocity of 5,000hto 6,000 feet per second as it emerges through the valve. As the liquid emerges into Space already filled, the velocity of the stream.must be retarded before striking against the side wall, but the fact that the metal wears away in the homogenizing head, is proof that there is an im- pact of the liquid against the side walls. Another theory is that the diSpersion results from the shearing of the fat globules as they pass through the liquid in the homogenizing head. This is due to the liquids traveling at different velocities. The clear- Ml: Tladf ance in the homogenizing valve may also be smaller than some of the fat globules and these would certainly be sheared in passing through. In the valve clearance, the liquid in contact with the metal would be retarded while the liquid in the center of the clearance would be traveling at a high velocity. In like manner there must be a great difference in the velocities of the liquid mixture as it leaves the homogenizing valve. The dispersion of the fat globules may also result from the explosive action caused by the compression of the liquid followed by a sudden re- lease of pressure. Since the compressibility of butterfat is very low this explosive effect would be slight. Effect of Viscolization on the Creaminggongilk Viscolization, or homogenization, as used in the dairy industry COD? sists of forcing milk or cream through small openings under high pressure. Butterberg (42) in 1905 was perhaps the first to report that when milk is homogenized, the fat does not separate. His method consisted of heating milk to 85° c. and forcing it, under 250 pounds pressure, through a tube of one millimeter in diameter and then between closely applied plates of agate and metal. Bishop and Murphy (45) further state that the fat of homogenized milk could not be separated by centrifugal separation nor could homogenized cream be churned. Cream from homogenized milk testing 5.5 per cent was found to test only 7.5 per cent fat while the skim milk tested 5.2 per cent. Later Hammer (5) reported that when milk is homogenized no cream layer is found. He attributed this loss of creaming to the breaking up of the fat globules, which have less tendency to rise than the original Us. III-.5. i...“ 4.! fat globules. Martin and Combs (6) Viscolized a sample of milk at 2,000 pounds pressure and compared its creaming ability with a check sample. The volume of cream rising on the check sample was 10 per cent while that on the Viscolized sample was two per cent. Troy and Sharp (7) observed that the fat is not clumped in homogenized milk. Doan (8) noted that the degree of clumping increased with the OOH? centration of the fat in the mixture. This lead him to conclude that the ratio of the amount of plasma colloids to the amount of fat in the mixture is the limiting factor in the fat clumping phenomenon. These results agree with Hening (9) who states that mixtures containing 5 to 10 per cent of fat clump but little while mixtures containing higher percentages of fat clump markedly on homogenization. Mortensen (10) found that by homogenizing cream the fat is brought to- gether in large clusters. Evenson and Ferris (18), Dahle and Martin (26), Sherwood and Smallfield (19), and Reid and mosely (52) have called atten- tion to the fact that homogenization of cream, or ice cream, not only causes a subdivision of the fat, but also causes a clumping of the fat globules. Reid (55) states that the clumping effect of ice cream is not influenced by changes in pressure of homogenization, while Doan (8) is of the opinion that clumping of cream increases as the pressure increases. Webb and Holm (27) also recognized the factor of fat clumping in their study of cream feathering. They suggested that the phenomenon may be due to the change of potential of the fat globules. Palmer and Anderson (28) have shown that heating the milk plasma de- stroys creaming. This agrees with Troy and Sharp (7) who state that cream— ing ability is dependent upon the ability of the fat to clump. They have further shown that heating the milk retards or destroys clumping. Like- wise Doan (8) found that heating the plasma also reduced the fat clump- ing when.milk containing 12 to 15 per cent fat was homogenized. Hening (29) has also shown that a temperature of 180° F. for 10 minutes diminr ished the size and number of fat clumps of homogenized ice cream mix. According to Doan (12) if fluid milk or cream containing eight per cent or more of fat is homogenized at a pressure of 2,000 to 5,000 pounds, a peculiar structure of the fat is created. The globules are greatly re— duced in size and tend to clump together in such a fashion as to occupy the greatest possible Space. He also concluded (12) (8) that such a milk or cream will not separate a cream layer regardless of whether the fat is clumped or not. However, if diluted with skim or whole milk, creaming takes place, the amount of creaming being greater as the fat clumping be- comes more pronounced, although samples containing no clumps form no cream layer on dilution with milk. “Viscglizedfi Milk The term "Viscolized" milk usually refers to that milk to which some Viscolized cream.has been added and which yields a definite cream.layer. Martin and Combs (6) were the first to give definite data which show the effect on the volume of cream rising on milk made from homogenized cream and skim milk. Later Doan (11) (12) and Troy and Sharp (7) have given similar data. Doan (11) reports that homogenization of a part of the milk decreased the creaming ability. Later Doan (12) homogenized 20 per cent cream at 110° F. under a pressure of 2,000 pounds and standardized it to four per cent butterfat with skim milk. He also standardized a four per cent milk using the same skim milk and unhomogenized cream. The volume of risen cream on the unhomogenized sample was 12 per cent while that on the homog— enized sample was 71.2 per cent. ~His results indicate that the greater the amount of cream Viscolized and returned to the milk the greater the cream layer, and also the richer the cream viscolized the larger the cream volume, although the cream volume does not correlate directly with the fat viscolized. This lead him to conclude that the factor exerting the great- est influence on the volume of cream rising is not the amount of fat ho- mogenized but the amount of cream in Which a given.amount of fat is cone tained. Doan interpreted this enormous increase in creaming ability to the looseness of packing of the fat clumps in the homogenized sample as compared to that of the normal sample. Microscopic examination of the homogenized milk showed the fat to be finely divided but gathered together in clumps containing hundreds of small globules, with no normal globules present, while the globules of the unhomogenized sample were large, mostly spherical, and individual in most cases, although a few clumps were present. To determine if the so called "Viscolized" milk could be heated with— out deleterious effects, Doan (12) pasteurized the milk spoken of above at 145° F. for 50 minutes. The volume of cream.on the homogenized sample was 40 per cent in this case, while that on the unhomogenized sample was 10.8 per cent. Microscopic examination of the homogenized sample showed smaller clumps along with a greater proportion of individual globules._ This would explain the decrease in volume of cream layer. The volume of creaming, how- ever, was still fOur times that of the normal milk. From this he concluded that pasteurization can be practiced without destroying the ability of ho- mogenization to increase the cream layer. 10 Milk exhibiting a larger cream layer than normal, considering the fat content, may be suspected of being Viscolized. This according to Doan (12) can be determined by a simple microscopic examination. By this method the sample of milk is mixed well and a small portion is transferred to a drop of water previously placed on a cover glass. The water and sam- ple are not mixed. The cover glass is then inverted over a depression slide and examined under a microscope. Normal milk will contain round globules mostly individual and fairly uniform in size. Any irregular dark patches indicate "Viscolized" milk. "Viscolized" milk may also come tain normal fat globules. This depends upon whether only a portion of the fat was homogenized in the form of cream. Along with the "visco-clumps" a comparatively large number of small globules help in the identification. Care must be taken to mix the milk well before the slide is made or too much fat may appear in the microsc0pic field. In this case the globules and clumps may appear too close together to distinguish the characteristics of the sample. Doan claims to be able to distinguish as little as one- half of one per cent of homogenized cream when added to milk by this method, even though this small amount had practically no effect upon the cream volume. Theogy of Viscosity Miscroscopical examination of the fat globules before and after homog- enization, showed that their average size had been greatly reduced. Accord— ing to Sommer (2) the increased viscosity produced by a given amount of fat is increased as the fat is divided into smaller globules. This is in ac— ll cord with Bingham's (45) discussion of emulsions who stated that a de- crease in the particle size of the dispersed phase also decreased the fluidity. Hatschek (54) was of the opinion that this increased viscosity was due to an adsorption film of the liquid phase around the particles, the thickness of which was independent of the degree of dispersion. Associates of Rogers (54) stated that by the process of homogeniza- tion, the fat globules are subdivided and diapersed throughout the medium. These globules are stabilized by a protein membrane formed at the fat liquid interface which prevents their coalescence. V Bateman and Sharp (14) are of the opinion that since the thickness of the adsorption film varied slightly, if at all, with the particle size, and the amount of adsorption depends upon the surface, more of the skim milk phase will be adsorbed in the case of whole milk. This resulted in an increased viscosity because of a decrease in the free liquid. Increased viscosity during aging is undoubtedly due to the altering of the proteins. argue: Viscoliza ion on Nisgm Numerous studies of the viscosity of whole milk and cream have been carried out. The methods used by the different investigators have varied greatly. This makes it difficult to compare the work of one experimenter with that of another. Viscosity according to Turnbow and Raffetto (1) may be defined as the resistance offered by a liquid to shearing, stirring or flow through a capillary tube. Buglia (15), and Bateman and Sharp (14) found that homogenization in- creased the viscosity of whole milk while it had no effect on skim milk. Wiegner (15) obtained similar results for that of whole milk. He attributed 12 this increase to the increased adsorption of the protein especially casein. Kobler (16) reported that viscosity of milk is due to both the fat and the protein content, it is diminished by skimming and dilution with water. The viscosity is also lessened by shaking, but returns to normal in about 10 to 12 hours. Taylor (1?) concluded that the viscosity of milk is not proportional to the total solids but is a function of the fat and solids not fat. Milk heated to 60° C. decreased in viscosity, but increased in viscosity when heated to 70° C. He attributed this later increase to coagulation. Evenson and Ferris (18) reported that homogenization at 5,500 pounds pressure increases the viscosity of milk as well as cream. Pressures of 1,200 pounds increased the viscosity of cream, but affected the milk only slightly. They also found that pasteurization at 62° to 65° 0. decreased the viscosity, but heating to 75° to 800 C. increased the viscosity. Mortensen (10) noted that cream decreased in viscosity by pasteuriza- tion, but homogenization increased the viscosity. Babcock (20) found that homogenization is very detrimental to the whipping prOperties of cream and this effect is increased as the homogenization pressure increases. Homog- enization and pasteurization together practically destroy the whipping properties of cream. Sherwood and Smallfield (19) indicated that the increase in viscosity of cream during aging can'be attributed to the greater grouping of the fat g16bules. Agitation caused a reduction.of the viscosity with a correspond- ing decrease in fat clumping. They also believed that the increase in.vis- cosity immediately after homogenization was due to the taking up, or fixing, of more of the milk serum on the increased surface of the fat globules. 15 Babcock and Russell (55) found that pasteurization‘bfoke up the clusters of fat globules present in raw normal milk, and they attributed the decrease in viscosity produced to the breaking up of the fat clusters. Wall (56) also pasteurized milk and cream and noted a decrease in viscosity. Pasteurization of skim milk decreased in viscosity slightly While pasteur- ization of whey increased the viscosity. Weinlig (57) heated milk to 600 to 65° c. and found that it decreased the viscosity when cooled back to the original temperature, but heating the milk to 80° 0. had the opposite ef- fect when the milk was cooled. He attributed the decrease in viscosity to a change in the casein, and the increase at higher temperature to evapora- tion of water along with changes in the albuhin. According to Bateman.and Sharp (14) pasteurization of skim milk at 62° C. for 50 minutes caused a slight decrease in viscosity when determined at 25° C. The viscosity of skim milk also progressively increased with age. This increase in.viscosity could not be brought back to that of the fresh sample by repeatedly running it through a capillary tube. They also re- ported that agitation may cause a decrease in the viscosity of milk contain- ing clumps of fat globules, due to the breaking up of the clumps. However, mechanical agitation produced no change in the viscosity of fresh skim milk or homogenized milk. Whitaker, Sherman, and Sharp (58) found that as the temperature is raised from 5° to 600 C., the viscosity of skim milk decreases faster than that of water; from 60° to 700 C. the viscosity of both decrease at the same rate; and above 700 C. the viscosity of skim milk decreases more slowly than.does the viscosity of water. Pasteurization of skim.milk for 50 mine utes between 40° and 72° C. caused a decrease in viscosity, while pasteuriza- 14 tion at higher temperature caused an increase. Whey decreased in viscosity when pasteurized below 60° 0., increased in viscosity from 60° to 100° 0. and decreased in viscosity from 100° to 1208 c. Dahlberg and Hening (25) stated that the viscosity of unhomogenized cream increased with aging and with increased percentage of fat, but both effects were variable. They also found that pasteurization slightly reduced the viscosity of milk and greatly reduced the viscosity of cream. Pasteur- ization largely inhibited the effect of aging. Doan and Minster (59) found that the use of a two stage homogenizer or double homogenization decreased the viscosity and fat clumping of milk as compared with the use of a single stage homogenizer. Dahle and Barn, hart (40) reported that homogenizing of ice cream mix at 170 to 1800 F. resulted in.a lower viscosity and greatly reduced fat clumping. Reid (55) and Reid and Garrison (41) stated that when the pressure on the first valve of the homogenizer is increased there is a resulting increase in the vis- cosity of the mix. However, when the pressure is increased on the second valve of the homogenizer, the viscosity is not always decreased, but may also be increased. Babcock (44) in.a recent article stated that homogenization of cream increased its viscosity. This increased viscosity is in direct relation to the homogenization pressure. However, the increase in viscosity due to homogenization at any definite pressure depended upon.the temperature at which the cream is homogenized. Rehomogenization of cream lowers the vis- cosity. Babcock also reported that the viscosity of cream increases as the per cent of solids not fat increases. 15 so 0 S face Te 3 on Surface tension.may be defined as the resistance of a liquid to rup- ture. According to Sommer (2), surface tension arises from the ferce of attraction between closely adjacent molecules. This force of attraction is toward the center at all times. However, the molecules within.the liquid have these forces balanced by other molecules which completely sur- round it. But with molecules at the surface only the lower half of this sphere of forces are balanced by similar forces. For this reason the molecules of the surface are pulled inward by the molecules of the liquid. The unbalanced forces may be thought to bend over to the surface. This re— sults in a state of stress at the surface which is known as surface tension. Getman (55) stated that some liquids like water wet the walls of a glass capillary tube, whereas others, like mercury, do not. In the first case the surface of the liquid is concave, while in the second case it is convex. The surface area in each case tended toward a minimum. Sarggce Iegsion Kolber (16) in 1908 was one of the first to study the surface tension of milk. According to his studies, factors which altered the viscosity al— so changed the surface tension. Burri and Russbaumer (46) discovered that the surface tension of milk decreased on aging. However, in milk where the temperature does not go lower than 20° 0., the surface tension fell but slightly, but cooling to 10° or lower produced a marked depression. The decreased surface tension due to cooling was permanent in character and could not be restored by heating the milk to body temperature. I11. hrll| ‘4 16 Bauer (47) confirmed the results of Burri and Nussbaumer, but stated that warming the milk at 500 C. almost restored the surface tension to its original value. He attributed this decrease in surface tension to the solidification of the fat. 0n the other hand Qualiariello (48) stated that the lowering of the surface tension by cooling to 100 C. or lower can not be undone by warming. He thought the glycerides of the higher fatty acids become solid at lower temperatures and liberated mixed lower glycer- ides which are slightly soluble in water, thus lowering the surface tens sion. Homogenized milk, he stated, has always a lower surface tension than normal milk, and is not affected by low temperatures. Dahlberg and Hening (25) found that the surface tension of milk and cream decreased with an increased fat content. It also usually decreased with aging. Pasteurization as a rule increased the surface tension and aging would not reduce it to normal. Behrendt (49) stated that the fat has no essential influence upon the surface tension of milk. He found that milk with a reduced protein con- tent has a considerably higher surface tension than normal milk. Doan.and Minster (69) found that the surface tension of milk was ir- regularly affected for both single and double stage homogenization, but when the fat content was more than four per cent, single stage homogeniza- tion increased the surface tension, whereas in skim milk it was lowered. They (50) also stated that homogenization lowers the surface tension of skim milk, except where the skim milk has been heated to a temperature of 1200 F., in which case there appears to be an increase. Homogenization of milk containing fat always increased the surface tension. If the viscosity 17 is increased greatly the effect is pronounced. Rehomogenization of the milk destroys the viscosity, which lowers the surface tension. Reid (55), who worked with ice cream mixes, found that the surface tension is increased as the pressure of homogenization is increased. 212.2922. of anggi‘gg A foam consists of a gas phase, which is usually air, dispersed in a liquid. The gas phase, according to the Associates of Rogers (54), is in the form of bubbles of microsc0pic size. Thus an air phase of enormous surface area is produced which is covered by film of micronic, or submi- cronic thickness. To produce these films, the surface tension of the liquid phase must be sufficiently reduced so that the active agents may spread into a thin film. However, Hillyer (51) has shown that a low sur- facs tension alone is not all that is required to produce a stable foam. The film must be sufficiently elastic so as to prevent coalescense of the air bubbles. Associates of Rogers (54) stated that the tendency of milk to foam when agitated is evidence that a surface tension depressant is present, which is this case is a protein. Rahn (52) believes the accumulation of an albuminous substance which passes into the walls of the foam cells, re- duces the surface tension causing the formation of a foam. If left undis- turbed, the foam falls leaving a thin wrinkled layer on the surface. This material is composed of a solid substance which is similar to that of al- buminous material, in that it appears irreversible. When cream is whipped it forms a network of solidified albuminous substance intermingled with solid fat having the form of foam. This foam is prevented from falling 18 by the fat. The chemical nature of this foaming substance is not known. It is different from that of albumin and is not casein. Otswald and Steiner (55) are of the Opinion that there is no rela- tionship between surface tension and foaming. Adsorption on the surface, such as fatty acids on water, or small colloidal particles on the surface of a liquid, is necessary to form a membrane before foam forms. Foaminnaqur Milk A thick stable foam is desirable in the whipping of cream or in the manufacture of ice cream. In the Operation of such machines as the sepa- rator, clarifier, or the filling of bottles, vats, cans, and so forth, the formation of foam presents a serious problem. Sanmann and Ruehe (25) heated raw whole milk and skim milk to 145° F. and homogenized it at several different pressures. These were cooled promptly in ice water and stored over night at 40° F. The foaming ability was then determined on both the check and the homogenized samples. Their data indicated that homogenization increased the foaming of whole milk at both 40° and 80° F. but decreased the foaming at 140° F. Skim milk showed a slight increased ability in all cases. They also found that with indi- vidual cows there was no relationship between the fat and total solids con- tent and its foaming ability. However, when the influence of individual characteristics of the milk was standardized the fat generally decreased the foaming ability while the solids not fat generally increased the foam— ing ability. Leete (24) also using mixed herd milk, reported that no defi— nite statement could be made regarding the effect of butterfat without cone sidering temperature. 19 Sanmann and Ruehe (25) studied the effect of temperature from 55° to 180° F., using pasteurized skim milk, pasteurized whole milk, and 20 per cent cream. They found the greatest amount of foam was produced at the lowest temperature. With increased temperature, the volume of foam decreased to a minimum at 70° to 800 F. for whole milk, 80° F. for skim milk, and 90° F. for 20 per cent cream. Further increase in.temperature resulted in an increase of foaming, to a second maximum of 110° F. for skim and whole milk and 120° to 150° F. for 20 per cent cream. At low temperature skim milk foamed most, whole milk next, and 20 per cent cream least. Pasteurization of whole or skim milk at 140° F. for 50 minutes had no effect upon the foaming of milk. Heating to 180° F. for 50 minutes caused a slight but regular decrease in foaming ability. Leete (24) found that skim milk and milk containing between three and five per cent fat had a minimum foamingalt from 20° to 50° C. Lower temp- eratures produced large amounts of light airy foam with large bubbles, while at higher temperatures, 50° to 80° C., the foaming also increased but the air bubbles were small. With cream, containing 18 per cent fat, the minimum amount of foaming occurred at 40° C. and increased to a maxi- mum at 80° C. A slight decrease in foaming occurred at 90° C. At lower temperatures, 40° to 20° 0., the foaming increased, then.gradually de- creased from 20° to 5° C. Leete also stated that immediate measurements of the foam on raw milk containing from three to five per cent fat showed more foam than on pasteurized milk under the same condition. While meas- urements made ' one minute later showed the pasteurized milk to have the greater foaming. One minute measurements were the same for both raw and pasteurized samples held 24, 48 and 72 hours. Immediate measurements of the foam on raw skim milk were greater than those on pasteurized milk while Dairy. i... a. .Fl..r . 20 the reverse was true at the end of one minute. Dahlberg and Hening (25) stated that a 50 cc. sample of pasteurized skim milk whipped to a volume of 230 cc. at 4.4° 0., while the same amount of raw skim milk whipped to a volume of 196 cc. at the same temperature. Skim milk also whipped to a much greater volume than milk containing 10 per cent fat. According to the Associates of Rogers (54) the tendency of milk to foam is at a minimum between the temperatures of 20° and 500 C. Below this range foaming ability increased with decreased temperature, while above this temperature foaming ability also increased rapidly. Pasteur- ization reduced slightly the foaming ability. As the fat content of the milk increased the temperature of minimum foaming shifted toe: higher temperature. According to Leete (24) aging at a temperature of 10° C. had but little effect on the foaming ability of either milk or cream. Skim milk showed a slight variation at 5° and 10° C. At these temperatures the im- mediate measurements showed a gradual increase in amount of foam after aging 24 and 48 hours, which was followed by a decided falling off after aging 72 hours. In.this case theiamount of foam was less than on the fresh milk, however, no such condition was found at the one minute measure» ment. Sanmann and Ruehe (25) found that the temperature at which milk is held is significant in determining the effect of’age on the foaming abil— ity of milk. Measurements made after the milk had been.held for three or four hours at 98° F. were almost identical with those of the fresh milk. Freshly drawn milk and milk held at 98° F. had approximately the same foam- ing ability at both 80° F. and 140° F. while in previously cooled milk the 21 foaming ability of the whole milk was much less at 80° F. than at 140° F. Milk held at 400 F. for three or four hours showed a slight decrease in foaming ability at 400 F., and a great decrease at 800 F. All milk showed the same foaming ability when measurements were made at 1400 F. These authors believed that the solidification and clumping of the fat globules when milk is cooled, influenced the foaming ability of the milk. tab 1 0 ca 5. Leete (24) believed that temperature is the major factor in foam stability. Low temperatures did not as a rule produce stable foams, where- as high temperatures produced quite resistant foams. Temperatures that pro— duced the least amount of foam also produced the least stable foams. As the temperature increased above that of minimum foam production, the sta- bility of the foam increased. For milk the stability of the foam was ap- proximately the same at temperatures of 50° to 90° C., while cream showed about the same amount of stability from 600 to 900 C. At temperatures of 50 to 100 C., skim milk produced a slightly stable foam, however, milk containing three to five per cent of butterfat produced practically no foam. Age had practically no effect upon foaming stability. The butterfat content also exerts an influence on foam stability. Dahlberg and Hening (25) found that milk with 10 per cent of butterfat gives a fairly stable foam while the foam from skim milk lacked perma— nency. This agrees with the Associates of Rogers (54) who stated that large increases of fat content not only increases the foaming but also stabilizes the foam. 22 Effect of Viscolizgtiog 03 the Specific Gravity Weigner (15) is of the opinion that there is no measurable change in the density of milk upon homogenization. Weinlig (57) states that definite influence on the specific gravity of milk could not be ascribed to pasteurization. Hahn (61) concluded that any decrease in the specific gravity of milk which occurs after passing through a separator, pasteur- izer, pump, or cooler, was due to the incorporation of air during the process. For this reason several hours is necessary for the specific gravity to return to normal. Eat Test of Viscolized Milk Butterberg (42) reported that the Adams test gave a much lower fat test on.homogenized milk than the Gottlieb method. Henseval (56) stated that some difficulty was experienced in applying the Gerber method to homogenized milk. Six samples of homogenized milk showed an average of 5.56 per cent by the Gerber method, 5.51 per cent by the Soxhlet method, and 5.65 per cent by the Gottlieb method. Likewise, Burr (57) concluded that the Rose—Gottlieb method was more accurate in testing for fat in homogenized milk than the Adams or Gerber method. Burr and Weise (58) in a later report stated that from 0.1 to 10 per cent of the fat remained in homogenized milk tested by the Gerber method over that tested by the Rose- Gottlieb process. Hudson (50) and Hollingsworth (4) stated that dealers have come to realize that a 5.6 per cent pasteurized milk will not yield a 5.6 per cent homogenized milk by the Babcock test. The reason given for this discrep- ancy is due to the fact that the fat globules are so finely divided that the smaller ones cannot be raised with the fat column in the Babcock Test 25 bottle. Doan and Swope (59) disagreed with the majority of investigators and stated that homogenization of whole milk or cream, even at high press- ures, exerted but little influence on the Babcock test. Stab 't of Proteig toward alcohol Homogenization, according to Doan (62), strikingly changes the pro- tein stability of milk where fat is present. He further shows that as the fat content increases, the stability of protein toward alcohol decreases, and this increase is much more rapid than that in unhomogenized samples. If no fat were present, homogenization produces no appreciable change in the alcohol number. Doan also examined the milk at the alcohol floccula- tion point under the microscope and found the floccules indistinguishable from fat clumps. He also found that samples containing 16 per cent fat gave a flocculated appearance when diluted with water alone. This suggests that the stability of the proteins may be dependent upon fat clumping. Webb and Holm (27) who studied the protein stability by the resistance of the sample to heat, found that increasing the fat content of homogenized cream decreased the protein stability as did also higher pressures of homog- enization. Doan (62) agreed that the same relationship exists as determined by the alcohol test.- When.the milk was heated before homogenization, Doan (62) reported that the proteins were rendered more stable. In other words, heating causes the protein to become more stable, thus reducing the effect of homogenization. This is in agreement with the results obtained by Webb and Holm (27) on cream. It has also been shown by Doan (8) and Hening (29) that heating the plasma inhibits the fat clumping. This agrees with Doan's (62) suggestion that fat clumping may influence the protein stability. Doan and Minster (50) 24 concluded that high temperature of preheating will not eliminate fat clump- ing in any of the mixtures containing over seven per cent fat, if the mixt- ure is subsequently homogenized at low temperatures. This, they stated, indicates that the precipitation of calcium ions is probably not as import- ant a factor as has been thought. Auzinger (64) concluded that the alcohol reaction with milk is not de- pendent upon the amount of acid present, but is probably caused by the trans— fer of calcium ions in its reaction to the protein substance. Later Sommer and Binney (66) demonstrated that the addition of calcium salts decreases the protein stability of milk protein in the alcohol test, while sodium citrate and disodium phosphate increases the stability. Since the total area of the fat surface is increased greatly by homog- enization, Sommer (2) quoted Tracy and Ruehe (65) as suggesting that the de- creased stability of milk protein as the result of homogenization may be due to the increased adsorption of phosphates and citrates at the fat-serum in- terface. This leaves less of these salts in the serum proper. Sommer (2) concluded that this explanation is in harmony with the observation that the presence of fat appears to be essential for the destabilizing effect of homogenization. Size cf Eat'globgles The main result of homogenization is the breaking up of the fat into many small fat globules. According to Butterberg (42), the fat globules in ordinary milk vary in size from 1.6 to 10 microns, while those in.homog- enized milk vary in size from 0.8 to 2.8 microns. Weigner (15) in.his studies found that the fat in normal milk averaged 2.9 microns and in ho- mogenized milk 0.27 microns. 25 Baldwin (60) observed that the degree of dispersion generally in- creased as the pressure increased. He found that the majority of the fat globules in homogenized milk ranged between one and two microns in diame- ter, whereas the majority of normal fat globules range in diameter from five to six microns. According to the Associates of Rogers (54) Rahn found that the greater part of the fat in homogenized whole milk was dispersed into globules of less than two microns in diameter. They also state that homogenization as carried out rendered the fat in a dispersed form more finely divided than the fat remaining in skim milk. Sommer (2) pointed out that the bulk of the fat in milk and cream ex- ists in globules of from six to eight microns and that properly homogenized ice cream mixes contain most of the fat in globules of between one and two microns in diameter. A globule of six microns in diameter upon homogeniza- tion.yields 216 globules of one micron, while a globule of eight microns diameter yields 512 globules of the same size. This decidedly changes the properties of the ice cream mix. Acidity of Viscolized Milk Schoops (68) and Istaz and Van Svest (67) concluded that homogeniza— tion does not increase the acidity nor noticeably alter the chemical com- position. However, Doan (62) gives data to show that the pH of raw milk is lowered whenever fat is present. This occurs regardless of whether the initial pH has been altered prior to homogenization. Alcohol tests were also made but this lowering of the pH accounted for only a small part of the protein stability. 26 Weinlig (57) and Rupp (51) found that pasteurization decreased slightly the titratable acidity of milk. This they attributed to the loss of gases during the heating process. Dorner and Widmer (70) found that the titratable acidity of raw milk increased as the pressure of homogenization increased, although the acidity did not develop at the same rate in all samples. Aging the raw homogenized milk showed a continued increase for 24 hours. Increasing the acidity markedly before processing prevented changes in acidity due to homogenization. However, the increase in titratable acidity found after homogenization of raw milk was not due to the action of bacteria. Iflaypr_af;Vi§galizedjhilk Doan (69) is of the opinion that homogenization may be carried out with comparable results on either raw or pasteurized milk. He cites one instance where the dairy short course students at the Pennsylvania State Dollege gave a preference for milk homogenized at 1000 F. over the same raw milk before homogenization. However, Dorner and Widmer (70) found that homogenization caused raw milk and raw cream to become distinctly rancid within a few hours. The development of rancidity increased as the homog- enization pressure increased. They attributed this rancidity to a lipase. Lipase was detected in all samples examined although the activity in differ- ent samples varied greatly. In unhomogenized samples the lipase acts so slowly that it cannot be detected, but since a greater fat surface is ex- posed in homogenized milk rancidity develops much more rapidly. This lipase was very sensitive to heat, milk held.at 55° c. for 20 minutes completely destroyed its activity. 27 Considerable disagreement may be found in the literature as to whether the enzyme lipase is present in normal raw milk. However, Nair (65) states that a true lipase is a normal constituent of raw cow's milk. This is indicated by an increase in titratable acidity of high butterfat cream preserved by sucrose and by rancid odors deve10pment. Pasteurization inactivates lipolytic enzymes. Chard Tension pf Xiacioili zed Milk The study of soft-curd milk has received considerable attention during the last few years because of its beneficial effects as an infant food. However, this study of the effect of viscolization on the curd tension of milk may be considered only as a preliminary report. Therefore, a complete review of literature will not be given. Washburn and Jones (22) found that the curd formed from homogenized milk did not become hard and tough as in the case of untreated milk. Ho- mogenized milk coagulated as promptly as did the control samples. However, its curd was so flocculent that it took five hours to precipitate it as compared to 20 minutes for normal milk. Hill (71) boiled milk and secured a curd which was only 51 per cent as hard as that of the original milk. However, pasteurization of the milk at 145° F. for 50 minutes had little effect on the hardness of the curd formed by its coagulation with pepsin. Hill (72) also stated that removal of fat renders the curd harder, while the addition of cream to the skim milk restored its normal curd tension. Espe and Dye (75) concluded that doubling the curd tension of milk in— creased the length of digestion period from 50 to 65 per cent. Boiling the milk lowered the curd tension markedly. However, acidifying the milk be- fore coagulation with rennin raised the curd tension. 28 PURPOSE OF EXPERIMENT The purpose of this experiment was to observe and to study the ef- fect of viscolization at different pressures, upon the following proper- ties, using both raw milk preheated to 52.20 C. (900 F.) and pasteurized milk heated to 62.80 0. (145° F.) and held for 50 minutes: 1. 4. 7. 9. 10. ll. Creaming ability of the Viscolized and unviscolized samples at 24 and 48 hours. Viscosity of the Viscolized and unviscolized milk at 200 C., both while fresh and after aging for 24 hours. Surface tension of the Viscolized and unviscolized samples immedi- ately after processing and after aging for 24 hours. Foaming ability of the Viscolized and unviscolized samples at 4° to 5° C. immediately after cooling. Titratable acidity, while fresh and after aging for 24 hours, as affected by viscolization. ‘ Butterfat content of the Viscolized and unviscolized milk as de- termined by the Babcock test. Specific gravity at 15° C. both of the Viscolized and unviscolized milk. Protein stability toward 95 per cent alcohol of the Viscolized and of the unviscolized samples. Size of fat globules both in the check and in the Viscolized samples. Curd tension of the Viscolized and of the unviscolized samples. Flavor of the Viscolized and of the unviscolized samples. IZIP. .'.. 29 PLAN OF EXPERIMENTAL WORK Somme lorflMillellaalx The milk supply used in this experiment was secured from two herds which delivered milk to the College Creamery. These herds were selected because each delivered daily approximately the amount of milk needed in the experiment. The first six experiments were carried out using milk from the herd number one, which consisted of four Holsteins, three Guern- seys, two Jerseys, and one Brown Swiss cow. Because of a shortage of milk supply from this herd at that time, the rest of the experiments were car- ried out using milk from the second herd, which consisted entirely of Hol- steins. All of the milk was delivered at a temperature of less than 65° F. madamental Methords The milk, as soon as delivered to the College Creamery, was taken to the experimental laboratory and placed in-a 50 gallon Cherry-Burrell coil type vat pasteurizer. It was immediately heated to 900 F. and a portion viscolized at 500, 1500, and 2500 pounds pressure. About two gallons of the milk was run through the viscolizer at the desired pressure before tak- ing samples to insure the proper processing at each pressure. The remain— ing milk in the vat, unless otherwise stated, was quickly heated to 145° F. and held for 50 minutes. This milk was then Viscolized at the pasteuriz- ing temperature using the same procedure as in the raw milk. The viscolizer used was a Union Steam Pump Company viscolizer of 200 gallon capacity, COD? taining "Duo-Visco" valves. Viscolized and check samples of the milk were taken in gallon ice cream cans. These were immediately emptied in pint bottles and cooled in 50 ice water. Samples for creaming ability were placed in 100 cc. graduated cylinders. These were also cooled in ice water. Unless used immediately all samples were stored in an electric refrigerator held at a temperature of 35° to 40° F. geagnihtignlgf Ire sit sr Made The creaming ability was determined by observing the cc. of cream appearing on 100 cc. graduated cylinders both at 24 and 48 hour periods. These observations were recorded as per cent. To insure that the samples were well mixed, all samples were poured from one bottle to another twice before any tests were made. Viscosity determinations were made by means of the Improved MacMichael Viscosimeter. In.all determinations, gauge wires, number 54, were used. These were standardized against distilled water at 20° c. by the following method: one hundred cc. of distilled water was placed in the dash pot and the pointer adjusted to the zero mark on the dial. The machine was then allowed to run until the reading on the dial remained constant. The read- ing was made in degrees M. deflection of the dial. This equaled one centi- poise. Therefore, the degrees M reading of the milk divided by the degrees reading of the distilled water equals the number of centipoise viscosity of the milk. In each viscosity determination 100 cc. of the milk sample were used. The milk was first tempered to 20° C. and placed in the cup on the turntable. After making the reading to the closest one-half degree M., the temperature of the milk was taken. The trial was repeated if the temperature varied more than one-half of one degree Centigrade. Before re- moving the sample of milk the movable index arm was checked to see if it was directly over the zero mark on the disc. 51 The surface tension of the milk was determined by the Du Nouy Tahsiometer on the same sample as the viscosity determination. This machine measures the force in dynes required to pull a platinum ring four cm. in circumference, free from the surface of the liquid. Before each sample was examined for surface tension the platinum wire was rinsed in distilled water and burned in a Bunsen flame. Each sample of milk was placed in a different petri dish which was previously boiled in cleaning solution. All readings were made at 200 C. plus or minus one—half of one degree. In all cases the readings used checked within one-tenth of one dyne. The foaming ability of the samples of milk was determined immediately after cooling by a method similar to that suggested by Sanmann and Ruehe (25). The method used was to place 200 cc. of the sample in a graduated 500 cc. tall form beaker, and whip it for one minute in an electric stir- ring machine such as is used at soda fountains in the preparation of malted milks. After one minute stirring, the agitator was withdrawn. Readings of’ the total volume of sample and foam were made 15 seconds after agitation. The volume of foam was calculated as the per cent of the original volume. Acidity tests were made by titrating with N/lO sodium hydroxide im- mediately after processing and again after aging for 24 hours. In order to increase the accuracy of the test 17.6 cc. samples were used for titrat- ing and the results were recorded in per cent of lactic acid. Because of the rise in acidity observed in the raw viscolized samples, a few trials were run to determine if preheating to 1450 F. and if pasteurizing after viscolization would show the same results. ‘VM-v— I I I l . l L 52 A Westphal balance was used to secure the specific gravity of the milk. All determinations were carried out at 15° C. Protein stability was determined by diluting two cc. of the sample of milk with the least amount of 95 per cent ethyl alcohol required to produce a noticeable trace of flocculation. The size of the fat globules were measured by means of an eyepiece micrometer. The milk used for this work was diluted with a one per cent solution of gelatin at the rate of one part of milk to 50 parts of gela- tin solution. This prevented Browning movement. One lOOpful of the di- luted milk was placed upon a slide and examined under a dry oil immersion lens of the microsCOpe. The average size of the fat globules was reported in microns. After most of the experimental work of this problem had been completed several trials were carried out to determine the effect of viscolization on the flavor of milk. Therefore, separate lots of milk were viscolized and held in order to study the flavor development due to viscolization. In one case the milk was viscolized as previously stated. In another trial raw whole milk, skim milk and milk standardized to the same per cent fat were used in the same manner. These latter samples were all from the same orig- inal source. Milk from the different patrons of the College Creamery was also viscolized at 2500 pounds pressure. All the samples were judged for flavor within two hours after viscolization and again after several hours, or until distinct off flavors appeared. The check samples were also held for several days to determine if the same off flavors due to age developed. 55 The curd tension of the milk was determined as suggested by Hill (72), using an American Curd—O-Meter. In each trial 100 cc. of milk was placed in the coagulation cylinder and heated to 95° F. Ten cc. of the coagulant, consisting of a mixture of three parts of 0.6 per cent solu- tion of one to 5,000 dry scale pepsin to one part of calcium chloride solution containing 578 grams of dry granular calcium chloride per liter, were added to each 100 cc. of milk. After standing for 10 minutes the knife of the Curd—O—Meter was gently pushed through the coagulated milk. The reading was recorded directly in grams. .flfl. r... m. 54 RESULTS QIXQaEiDEL of list: cilized Milk That viscolization destroys the creaming ability of milk has been known for several years. However, the effect of varying pressures of viscolization on the creaming ability of milk is not so generally under- stood. Table I shows the creaming after 24 hours of both raw and past- eurized milk viscolized at 500, 1500, and 2500 pounds pressure. Pressure as low as 500 pounds was not efficient in completely destroying the cream layer. The average of 12 trials shows the cream layer of raw unviscolized milk was 15.5 per cent while that viscolized at 900 F. under 500 pounds pressure was 1.85 per cent. Likewise, the milk pasteurized at 1450 F. for 50 minutes before processing at that temperature reduced the cream layer from 12.42 per cent in the raw milk to 0.65 per cent when viscolized at 500 pounds pressure. This shows greater creaming of the milk viscolized at the lower temperature. However, the creaming ability of the sample vis— colized at 500 pounds pre3"ure varied from zero to six per cent in the raw milk and from zero to two per cent in the pasteurized milk. .In no case was there enough creaming to measure in the samples viscolized at the higher pressures regardless of the temperature used. Table II indicates that the cream layer of milk viscolized at low pressure continues to increase even after 24 hours while that of the unvis— colized samples decreases. The average of the 12 trials shows that the raw unviscolized milk decreased 1.08 per cent in cream volume while the samples ‘viscolized at 500 pounds pressure increased 0.62 per cent in cream volume. In like manner the pasteurized unviscolized milk decreased 0.55 per cent in cream volume and the pasteurized milk viscolized at 500 pounds pressure 55 Table I. Effect of Viscolization on the Per Cent of Cream Rising on Raw and Pasteurized Milk Held 24 Hours after Processing. -‘L A *4 AA A.‘4¥J4_L14A__4_AA ‘L‘JAAAJAAAJA—A# 4A44+A A111_1 Raw (899 F.A1 A AAAA: A PasteurizedALI45 FA.):AAA1 Lot Pounds Pressure of Viscolization : Pounds Pressure of Viscolization go. 11 DA A A A A5AOpAAAA1 1500112500 A1AA ALA A 01 A A A5OO1A A A A A1590 11125001 1 14 5 trace - z 12 2 trace - 2 16 1 - - : 14 2 - - 5 17 trace - - : 16 trace - - 4 16 2 - - : 15 1 - - 5 l7 - - - : 10 - - - 6 15 5 - - : 11 trace - - 7 15 - - - : 12 trace - . - 8 14 6 - - : 15 trace - - 9 16 - - - : 15 - - - 10 15 l — - : 14 trace 4 - 11 15 2 - - : ll 1 - - 12 16 2 - - : 10 1.5 - - AVAeA-A A ALSaSll AleAQZLA _ A-A w A A A A-: AA A A:A . 12.42 ADA-£5 ll AlA-AA AA A A-A lA l Table II. Effect of Viscolization on the Per Cent of Cream Rising on Raw and Pasteurized Milk Held 48 Hours after Processing. QAAAgAgA AAAHA—HAAA A _‘_‘_.‘L L 1A ARawA [909 F .1 A A AA A:A PAasLtAeurized (1459A AFA 1 Lot Pounds Pressure of Viscolization : Pounds Pressure of Viscolization Alia-A A AAAOAAlA A502 A A 111500 1 2500 1A : A “0111509 A AA A “1509 AA 2ASAOOA Al 1 14 5 trace - : 12 2 trace - 2 15 l — - : 14 2 - ~ 5 15 trace - - : 14 2 - - 4 14 5 l - : 12 2 1 - 5 15 1 trace - : 10 1 - - 6 15 7 - - : 11 trace - - 7 14 l - - : 12 1.5 - - 8 l5 7 - - : 12 l - - 9 15 1 - - : 12 l - - 10 14 1.5 - - : l4 1 - - 11 15 2 - - : ll 1 - - 12 16 2 - - : ll 2 - - Ave.A A14. 42 2.A45A AQ.Q81AAAA 11A : 12.09 1.57 0.08 - increased 0.74 per cent in cream volume. At the 48 hour interval only one sample shoved enough creaming to measure when viscolized at 1500 pounds pressure. In no case was any creaming shown at 2500 pounds press- ure. [‘3 (D Q; '3’ I :a 9"" 5.1 s' Viscosity of Viscol; The viscosity of raw milk may be either increased or decreased by viscolization as shown in Table III. The general trend, however, is an increase in Viscosit due to viscolization. Seven of 11 trials show that the viscosity of raw milk is increased by viscolization, five of which indicate that the viscosity increases as the pressure increases. 0n the other land, two trials showed a decreased viscosity by viscoliza— tion and two samples were affected irregularly. The average of the 11 samples indicates that the viscosity of raw milk is increased by visco- lfzation in proportion to the pressure used. The average results after agir? raw milk for 24 hours show an in- crease in viscosity due to viscolization. However, as shown in.Tab1e IV, the viscosity of any one sample may increase, decrease or remain the same as compared to the determination made 24 hours previously. Immediate measurements of viscosity on the milk pasteurized prior to viscolization show a decrease in every case. The results are shown in Table III. Five samples were lowered in viscosity as the pressure increased. In the remaining samples, as the pressure increased, the viscosity was ir- regularly affected, but was always lower than that of the unviscolized milk. The average of the 11 trials shows the pasteurized unviscolized milk to have a viscosity of 2.142 centipoises; that viscolized at 500 pounds press- ure 2.957 centipoises; 1500 pounds pressure 1.869 centipoises, and 2500 pounds pressure 1.814 centipoises. 57 Table III. Effect of Viscolization on the Viscosity of Raw and Pasteurized Milk Immediately after Processing. The Viscosity Is Expressed in Centipoise at 20° C. AAAA ¥A ~k- LAA ‘_ LFAg AL-hhh»h—n ~‘v nun-vb- is A AA say; mail 11A A A LA .: :A PAa'éit‘Aé'msz-ed"(fi5°F.) Lot Pounds Pressure of Viscolization : Pounds Pressure of Viscolization ITO. 0 500 1590 2500 : 0 599 L L 1590 LLLZLSOQL L L LL_L_ 1 1.58 1.75 1.88 2.15 z 2.18 1.85 1.82 1.85 2 2.12 2.09 2.24 2.24 : 2.06 2.05 1.87 1.81 4 2.18 2.21 2.55 2.51 : 2.27 2.18 2.00 1.64 5 2.24 2.18 2.12 2.55 : 2.24 1.82 1.79 1.82 6 2.12 2.00 2.09 2.06 : 2.00 1.79 1.79 1.67 7 2.15 2.26 2.26 2.25 : 1.97 1.90 1.85 1.70 8 2.50 2.20 2.15 2.00 : 2.57 1.80 1.77 _ 1.77 9 2.27 2.50 2.57 2.45 : 2.27 2.05 1.90 2.00 10 2.55 2.40 2.57 2.57 : 2.20 2.17 1.95 1.87 11 2.17 2.55 2.40 2.47 : 2.25 2.15 2.15 2.15 12 2.25 2.26 2.26 2.47 : 1.85 1.80 1.75 1.70 Age. L2.l§2flfl2.178JLL2.24lLJLgt515 LLL; 2.142LL1,¢_4 L14869LLL1.813LLLLL Table IV. Effect of Viscolization on.the Viscosity of Raw and Pasteurized Milk Held 24 Hours after Processing. The Viscosity Is Expressed in Centipoise at 200 C. A A AAA AA fiawitéb: F.) is A As A All 4..-“: P? .5 Eeuaizei (145“ 3.) A1: A Lot Pounds Pressure of Viscolization : Pounds Pressure of Viscolization No. 0 500 LL1L50L0L AL 2500 L L L L:_ LL 0 L 590 L L __1L590L LL LL2§LQQL L L 1 2.18 2.12 2.18 2.24 : 2.15 1.76 1.67 1.67 2 2.24 2.50 2.56 2.48 : 2.50 2.15 2.06 2.09 4 2.09 2.15 2.27 2.42 : 1.97 1.97 2.05 1.97 5 2.12 2.21 2.27 2.50 : 2.12 2.06 2.00 2.05 6 2.15 2.15 2.50 2.50 : 2.00 1.90 1.85 2.05 7 2.07 2.55 2.26 2.25 : 1.67 1.97 1.95 2.00 8 2.20 2.17 2.50 2.27 : 2.27 2.00 1.97 1.90 9 2.55 2.27 2.55 2.57 : 2.55 1.90 2.00 2.07 10 2.50 2.47 2.57 2.60 : 2.57 2.50 2.25 2.20 11 2.20 2.27 2.50 2.45 : 2.20 2.15 2.15 2.15 12 2.26 2.16 2.56 2.27 : 2.55 2.20 2.20 2.07 Ave. L 2.19le LL2L.2L5L6L LL L2.L5L46LL L2 . 55 _5 : 2.155 2.051 3;.01121 $.014L L A ll AA 58 Aging all of the samples for 24 hours after viscolization increased the average viscosity although individual samples were affected irregular- ly. Eight of the 11 samples still showed a decreased viscosity due to viscolization of the pasteurized milk; one showed an increase in viscosity; and two were affected irregularly. gpggace TensionLgfLViscolized Milk Results of surface tension study indicate that the surface tension of unpasteurized milk is always lowered by viscolization. However, the de- crease in surface tension does not lower as the pressure increases. Table V shows that the surface tension was lowest at 1500 pounds pressure in nine of 12 times. The 2500 pound pressure samples showed the lowest surface tension only twice, while the 500 pound pressure of viscolization was also lowest twice, one of which was the same as that at 1500 pounds pressure. The average of 12 trials shows the surface tension of the unviscolized raw milk to be 45.62 dynes; that viscolized at 500 pounds pressure to be 59.61 dynes; that viscolized at 1500 pounds pressure 58.47 dynes; and that vis- colized at 2500 pounds pressure 59.16 dynes. Table V also shows that the surface tension of pasteurized milk was as a rule increased slightly by viscolization. However, in two trials the surface tension of the milk viscolized at 500 pounds pressure appeared, one-tenth of a dyne lower than that of the unviscolized milk. In only one trial was the surface tension at 1500 pounds pressure slightly lower than that at 500 pounds pressure. At 2500 pounds pressure the surface tension was always the same or higher than that of the other samples. The average of the 12 trials shows the surface tension of the pasteurized milk to be 59 Table V. Effect of Viscolization on the Surface Tension of Raw and Pasteurized Milk Immediately after Processing. The Surface Tension is Expressed in.Dynes at 20° C. ‘4 ,Baw L900 F.) g A z, W Pasteurized (14s: L) ‘44 Lot Pounds Pressure of Viscolization : Pounds Pressure of Viscolization NOLA - 90 A k 400 A; H1500 M 2500 5A pgkg 500 A 1500gg 2500 H 1 46.1 41.6 59.1 59.7 : 45.9 46.9 46.6 47.0 2 44.5 41.2 59.4 59.5 : 46.4 46.5 46.5 46.5 5 44.8 42.0 41.4 40.4 : 45.1 46.5 46.4 46.8 4 44.1 59.7 58.5 59.6 : 42.6 45.5 45.6 45.8 5 42.0 57.0 57.8 59.5 : 45.2 45.5 45.9 44.1 6 42.8 59.5 57.5 57.6' : 45.8 45.7 44.5 44.9 7 42.5 58.0 58.0 59.2 : 44.0 44.6 44.9 45.1 8 45.2 59.5 58.7 59.7 : 44.4 44.5 44.8 45.0 9 44.4 40.5 58.9 59.7 : 44.0 44.8 45.2 45.7 10 45.1 59.5 59.1 59.5 : 45.2 45.1 45.8 46.0 11 45.6 58.5 57.5 57.9 : 44.7 44.9 45.5 45.5 12 42.5 58.5 56.0 57.8 : 45.0 45.5 45.8 46.5 la 4 44.; 11515.19] 1 515431 assess. in glegwgasg A 59.61, #155,511; sane f Table VI. Effect of Viscolization on the Surface Tension of Raw and Pasteurized Milk Held 24 Hours after Processing. The Sur- face Tension Is Expressed In Dynes at 20° C. an A in 5.3.3499?er in ;l r it : a a Re sjcearizgallasa LL 4 in Lot Pounds Pressure of Viscolization : Pounds Pressure of Viscolization Jig-l l A Di. “509i illlSDlQ li.2_599 A l Also; in §QQ _ 4500 - ‘ lgsoodil : 1 45.6 45.0 57.5 57.5 : 46.5 46.4 46.6 46.7 2 44.5 40.5 54.5 55.8 : 44.9 44.5 45.5 45.5 5 45.5 58.8 59.0 58.5 : 44.5 45.5 45.8 46.5 4 42.5 57.2 55.0 55.8 : 45.2 45.0 45.1 45.9 5 45.5 54.9 54.8 55.5 : 45.5 45.2 45.5 44.5 6 42.5 57.5 55.5 55.0 : 45.8 45.5 44.4 44.8 7 42.5 57.7 55.0 55.5 : 45.8 44.5 44.5 44.7 8 44.2 59.2 57.5 57.0 : 44.6 -45.4 45.5 45.7 9 44.2 40.0 57.0 57.0 : 44.8 45.2 45.5 45.9 10 42.8 58.5 54.0 56.5 : 44.0 44.2 45.4 45.6 11 45.2 57.5 55.0 55.5 : 44.5 44.6 45.0 45.5 12 41.9 57.5 55.0 54.5 : 44.8 44.9 45.9 45.9 Ave. 45.56%58.A51 g 55.47 56:11, : 44.59 44.54 45.06% 45.442 pg 40 44.54 dynes; that viscolized at 500 pounds pressure 44.97 dynes; at 1500 pounds pressure 45.27; and at 2500 pounds pressure 45.55 dynes. Aging the milk for 24 hours appeared to cause a slight decrease in the surface tension of the pasteurized milk and a more marked de- crease in the raw milk, as shown in Table VI. However, the aged past— eurized and viscolized milk was irregularly affected, but the average of the 12 samples shows a slight decrease. The raw viscolized milk ins dicates slightly different results. In this case the milk viscolized at 1500 and 2500 pounds pressure was always lower in surface tension. Raw milk and viscolized milk at 500 pounds pressure were both irregular- ly affected but the average shows a slight decrease. Ejoaggi pg of Viscolizgd‘yil}; The foaming of milk is of considerable importance in the prepara- ‘tion of market milk. In this study foaming was determined only at low temperatures such as might be used in the bottling of milk. The results of this study as shown in.Table VII indicate that foaming ability, as car- ried out, is reduced by the viscolization of raw milk while pasteurization has the opposite effect. Pasteurization alone appeared to affect the foam— ing ability irregularly. The viscolization of raw milk always lowered the foaming ability, however, the pressure at which the minimum foaming occurred is not necessarily the highest one used. In only four out of 12 trials did the foaming decrease directly as the pressure increased. In two trials the foaming at 1500 and 2500 pounds pressures was the same. ‘ However, in six of the 12 trials 1500 pounds pressure gave the lowest foaming. Viscolization of raw milk at 500 pounds pressure always gave the same or a higher foaming ability than at 1500 pounds. This relationship did not 41 Table VII. Effect of Viscolization on the Foaming of Raw and Pasteurized Milk Immediately after Processing. The Foaming Ability Is EXpressed in Per Cent at 40 to 50 C. L—AL-A hL-‘AA—A -LAkk- FA—LA—AL‘AA‘ 4+; _._ 4449*— gL ALL _# kRawL flair.) w my Wu 3; LgPasteurigzed (1453 LL Egg Lot Pounds Pressure of Viscolization Pounds Pressure of Viscolization Hog, A p 0 A __50Q g 1500 g 2500 g 1+0 g; 300 A 1500 2500 ___ 1 122.5 112.5 60.0 50.0 150.0 157.5 162.5 162.5 2 145.0 95.0 82.5 82.5 127.5 150.0 157.5 162.5 5 120.0 75.0 70.0 67.5 110.0 112.5 157.5 140.0 4 150.0 75.0 75.0 77.5 125.0 145.0 150.0 160.0 5 140.0 87.5 82.5 92.5 145.0 142.5 160.0 162.5 6 150.0 107.5 77.5 75.0 120.0 140.0 162.5 162.5 7 140.0 115.0 87.5 100.0 140.0 155.0 157.5 157.5 8 157.5 115.0 105.0 105.0 157.5 150.0 152.5 150.0 9 155.0 105.0 100.0 92.5 142.5 142.5 152.5 160.0 157.5 85.0 72.5 75.0 125.0 157.5 150.0 157.5 122.5 55.0 47.5 67.5 127.5 152.5 150.0 160.0 112.5 60.0 47.5 67.5 87.5 92.5 112.5 127.5 ve. 151.0 90:6 75.5 79:4; 126.5 __59 8 _150.4 _155.2 42 hold when comparing foaming at 500 and 2500 pounds pressure. In this latter case four of the 12 samples showed a greater foaming at the higher pressure. The average of 12 trials shows the foaming of unviscolized raw milk to be 151 per cent; that viscolized at 500 pounds pressure 90.6 per cent; that at 1500 pounds pressure 75.5 per cent; and that at 2500 pounds pressure 79.4 per cent. As the pressure of viscolization increased the foaming ability of pasteurized milk either increased or remained the same, except in one case at 500 pounds pressure when the foaming was slightly less than that of the check pasteurized sample. However, the average shows a gradual increase in foaming from 126.5 per cent in the pasteurized unviscolized sample to 155.2 per cent when viscolized at 2500 pounds pressure. While the foaming ability of raw viscolized milk was always less than that of the pasteurized viscolized milk, its foam appeared more stable. The air cells were also much larger in the raw viscolized milk and had a rather frothy appearance which broke down slowly. The air cells in the pasteurized viscolized milk were very small and appeared to break down rather rapidly. ‘ Enabilityiolii Erntein Viscolization of whole milk not only disperses the fat, but in every case it also lowered the stability of the protein toward alcohol. Table VIII shows that the proteins of viscolized milk were less stable to 95 per cent alcohol than that of the original milk. However, milk pasteurized before viscolization is considerably more stable to alcohol than that of raw milk. 45 Table VIII. Effect of Viscolization on the Protein Stability of Raw and Pasteurized Milk Immediately after Processing. The Protein Stability Is Expressed in cc. of 95 Per Cent Alcohol to Co- agulate Two cc. of Milk. _gg_ggkfiaw;(90°AF.)LF#~## __ k_A : AAflPasteurizedklefiva,)_A AL_LA_ Lot Pounds Pressure of Viscolization : Pounds Pressure of Viscolization lioafffpf- i - 500i 111509 if 2509 ii 31 - Diff L159!) iii 15091112590 - i 4 2.1 1.5 1.0 0.9 : 5.6 2.9 1.7 1.6 5 5.5 1.2 1.1 1.1 : 5.6 5.5 5.2 2.8 6 5.4 1.9 1.0 1.0 : 5.4 5.2 5.2 5.1 7 5.5 2.2 1.1 0.9 : 5.5, 5.1 2.9 2.6 8 1.2 1.0 0.8 0.8 : 5.4 2.7 2.5 2.5 9 1.6 0.7 0.7 0.7 : 5.5 2.5 2.5 2.2 10 5.5 1.9 0.9 0.8 : 5.5 5.2 2.7 2.0 11 1.7 1.0 0.8 0.5 : 5.5 5.0 5.0 5.0 AyB-c.2o5.f 1:4; L g0.92 k 0.84 : g5.46 5.01 2:69 _ 2.47, A 44 Table VIII also indicates that as the pressure of viscolization in- creases the destabilizing effect becomes more pronounced, but this effect is far less marked in the pasteurized milk. In other words, only one- third as much alcohol was required to produce a visible coagulation of the milk protein in raw milk viscolized at 2500 pounds pressure as in the pasteurized milk viscolized at the same pressure. Titgatable‘Acidggy The titratable acidity is increased in every case by the viscoliza- tion of raw milk. However, if the milk is pasteurized before viscolization no such raise in acidity is apparent. This is shown conclusively by Table IX. According to this table, the titratable acidity of raw milk always in- creases or remains the same as the pressure increases. The average of 12 trials shows the raw unviscolized samples to contain 0.175 per cent acidity; milk viscolized at 500 pounds pressure 0.195 per cent acidity; 1500 pounds pressure 0.201 per cent acidity; and 2500 pounds pressure 0.208 per cent acidity. These results might be interpreted to show that the titratable acidity of viscolized raw milk is less rapid as the pressure increases. Results after aging for 24 hours show the same trend as that stated above. Table X shows no marked change in titratable acidity if the milk had been pasteurized previous to viscolization. However, the titratable acidity of the raw viscolized milk continued to increase to a greater ex- tent than that of the raw unviscolized milk. It appears from‘Tables IX and X that the average titratable acidity of the fresh milk increased 0.008 per cent; that viscolized at 500 pounds pressure 0.012 per cent; 1500 pounds pressure 0.056 per cent; and 2500 pounds pressure 0.057 per cent. 45 TableIX. Effect of Viscolization on the Titratable Acidity of Raw and Pasteurized Milk Immediately after Processing. The Titratable Acidity Is Expressed in.Per Cent Lactic Acid. AA—AiLgA—AA—HLLL ~kkg‘4k‘4“ LL A# #4 ¥A¥LFALLA¥ 11 infirm 190911" .) A A if f- 111 flan jesteurihed 114531131 r in 1 Lot Pounds Pressure of Viscolization : Pounds Pressure of Viscolization Moi-111101 11.599. iii 159911, 2509 A- A: f- 9. if 1-50911111115109i1215QQ 1.1 1 .190 .195 .250 .250 : .180 .180 .180 .180 2 .175 .185 .185 .200 : .165 .170 .170 .170 5 .160 .190 .190 .200 : .160 .160 .160 .160 4 .195 .220 .250 .240 : .190 .190 .190 .190 5 .160 .175 .195 .195 : .155 .155 .155 .160 6 .175 .195 .210 .220 : .170 .170 .170 .170 7 .175 .190 .195 .200 : .165 .165 .165 .165 8 .175 .195 .200 .200 : .170 .170 .170 .170 9 .175 .185 .185 .190 : .160 .160 .160 .160 10 .180 .200 .210 .215 : .175 .175 .175 .175 11 .175 .195 .195 .205 : .175 .175 .175 .175 12 .170 .185 .190 .195 : .170 .170 .170 .170 AyegkAél75AAgA¢1§A5g_A 5201; g .20§LAA {g .leQ.. .170.111elZQc .170,44_ Table X. Effect of Viscolization on the Titratable Acidity of Raw and Pasteurized Milk Held 24 Hours after Processing. The Ti- tratable Acidity Is Expressed in Per Cent of Lactic Acid. — gay ( 90° F.) Fasgefiized (145911.); A A A Lot Pounds Pressure of Viscolization; : Pounds Pres sure of Viscolization 1101.1 A IL A 50fo - .1le09 .1 .2599 if - .11 D. 500 1500 2500 5 .165 .190 .210 .220 : .160 .160 .160 .160 4 .205 .255 .260 .270 : .195 .195 .195 .195 5 .160 .180 .200 .215 : .155 .155 .160 .165 6 .190 .210 .255 .255 : .170 .170 .170 .170 7 .180 .195 .255 .240 : .175 .175 .175 .175 8 .180 .205 .240 .245 : .175 .175 .175 .175 9 .190 .205 .220 .225 : .175 .175 .175 .175 10 .180 .215 .265 .265 : .175 .175 .175 .175 11 .185 .215 .270 .270 : .175 .175 .175 .175 12 .180 .200 .255 .255 z .170 .170 .170 .170 ,AgeLAA5152 .295111152574AA_g§4§ : 4.175 gl7§-A-,x115 .lZ5AAg 46 Since only 0.008 per cent of the acidity as shown in the unviscolized sample could be attributed to bacterial origin, viscolization must have been responsible for the marked increase at the higher pressures. Preheating the milk to 1450 F. before viscolization apparently pro- hibited the increase in acidity caused by viscolization. Results of two trials as shown in Table XI show this very clearly. Pasteurization of the raw milk after viscolization at 900 F. appar- ently did not prevent the titratable acidity increase. However, as shown by Table XI the acidity after aging 24 hours showed no increase in one case and only a slight increase in another. Because of the rise in titratable acidity always noted in viscolized whole milk, several samples of skim milk were also viscolized. No change in acidity was observed as shown in.Table XI. This would indicate that the rise in titratable acidity due to viscolization must be associated with the butterfat content of the milk. 23,59,ch Test of Viscoli‘gdjgzlk It appears from this study that viscolization has little, if any, effect on the Babcock test of whole milk. If the size of the fat globule directly influenced the Babcock fat test, it would be expected that the butterfat content as shown by the Babcock test would be lowered as the pressure increased. The results in.Table XII show that no such condition exists. In no case does the results at different pressures vary more than two-tenths per cent and then only in the results of the first four experi- ments. Considerable difficulty was experienced at this time in securing 47 ‘4‘1‘11‘l4 W1 1 4 4111411 .m com nonwoaoum l1‘1‘111‘1‘1141] own. oma. omH. 00H. u omH. owd. 00H. 00H. AHA: swam tum ma u .h oom cmvmmnmnm owH. owfi. OmH. Cod. « Oma. Cod. OmH. omH. mas: Edam tum «a ova. Qua. Qua. 05H. « ova. Qua. 05H. 05H. .m owed copwmAmem ma mua. mna. mea. mud.. « mud. mud. med. mud. .h omea copwmnohm Ha u mqwmmoooum Ampmw ,y com. com. mma. owa. " com. com. mad. omH. omufihsmpmwm Ha u wufimmmoonm nmumm 0mm. mam. oow. med. ” mam. cam. cow. mud. @mNfiHSmpmwm OH 11 comm, 1 82 1 com o J " 8mm 4 18me t {84m 1110 J i J t -Iaom noapweaaooma> mo madmmmnm meadom » goapmufiaoomd> mo mndmmohm meadow pnmepwona aoq « \muflmmm00hm,uopmw mhdom em wwfimmmoopm nmpwd AflopmwcmfisH lililil Jill 14“ {4‘ 14414 Jill lJJJ‘JJ+ 41‘ J14 [444111 1 [4+4 141 J J11<11|1 .@Ho< ofiwowq 9:00 pom aw Ummmmnmxm mHathuHo¢ manwpmnpwa one .mcfimmoooum gowns cmufihdmpmwm MHHE 3mm mo new .h owed on vopwmnonm xfifiz mo hpfivwo< mapwpwpuwa map.no noavmnaaoomw> mo pommmm .HM canes 48 Table XII. Effect of Viscolization on the Percentage of Fat as Deter- mined by the Babcock Fat Test. gig—AAQAAAALAAJJ L-‘A‘AJALQAWJ AAAAJAA444‘4_A AJL‘4A -HJaEKSEQS Llawa atEuEizE . 1:458:11 J: A . A ll Lot Pounds Pressure of Viscolization Pounds Pressure of Viscolization floral; #0; ”if liQQ - iii .LS‘QOllU 42599444 :. A - AQaiiileQ A ll #355490. LPTZSAQQ A a A 1 5.50 5.25 5.20 - 5.50 : 5.50 5.50 5.25 5.50 2 4.00 5.85 5.85 5.80 : 4.00 5.90 5.90 5.90 5 4.20 4.10 4.10 4.15 : 4.20 4.20 4.15 4.10 4 4.00 4.00 4.05 5.95 : 4.05 4.10 5.9 4.10 5 5.85 5.85 5.90 5.85 : 5.85 5.85 5.90 5.90 6 5.25 5.20 5.15 5.20 : 5.25 5.20 5.20 5.15 7 5.50 5.50 5.45 5.45 : 5.50 5.45 5.45 5.45 8 5.25 5.50 5.50 5.25 : 5.25 5.50 5.55 5.25 9 5.60 5.60 5.55 5.60 : 5.60 5.60 5.60 5.60 10 5.70 5.70 5.70 5.70 : 5.70 5.70 5.70 5.75 11 5.60 5.65 5.60 5.60 : 5.65 5.60 5.60 5.60 12 5.85 5.80 5.80 5.85 z 5.80 5.80 5.85 5.80 Ave. 5.67 5.65 5.64 5.64 : 5.67 5.67 5.65 15.66 HJ k‘AJAWA A#_ A__A_.‘AAJ_4_‘_44__A ##A l A‘A4A‘A ~_‘ . 444A_._4_A AAAAAJ AA_4_444_‘_* ,h Jilin .: 73....” smith 5 .1? . fir}.4«t.. an. f49 clear tests, due to the use of too strong acid. After standardizing the sulphuric acid to a specific gravity of 1.82 to 1.85, no difficulty was experienced. Specific Gravity of Viscolized Milk The results of this experiment indicate very clearly that viscoliza- tion has no effect upon the Specific gravity of milk. Slight variation as shown in Table XIII might be explained as due to slight differences in temperature or to the incorporation of small amounts of air during the mixing process. gfiggngLIhtpglpbules The principal physical effect of viscolization of whole milk is the breaking up of the fat into many small globules. Results in Table XIV Show the globules to be broken down from an average of 5.88 microns in whole unviscolized milk to an average diameter of less than 1.5 microns in the milk viscolized at 2500 pounds;pressure. It appears that the degree of dispersion depends not only upon the pressure used but also upon the tem— perature of viscolization. The fat globules in the milk viscolized at 900 F. were not as finely dispersed as those viscolized at higher temper- atures even though the pressure of viscolization remained the same. Although the average diameter of the globules was greatly reduced, the size of the individual globules varied greatly. The average for the largest fat globules in the whole milk was found to be 15.57 microns while the largest for the milk viscolized at 2500 pounds was found to be between 5.5 and four microns in diameter. 50 Table XIII. Effect of Viscolization on the Specific Gravity of Raw and Pasteurized Milk as Determined at 15° C. flaw (900 E.) : Pasteurized £145UXE.E Lot Pounds Pressure of Viscolization : Pounds Pressure of Viscolization rummagingsoo8111159011alarmingly”allaqqiiigoalA.252in 1 1.0516 1.0516 1.0516 1.0516 : 1.0518 1.0515 1.0515 1.0516 2 1.0516 1.0514 1.0515 1.0515 ‘ : 1.0516 1.0516 1.0516 1.0515 5 1.0515 1.0514 1.0510 1.0511 : 1.0515 1.0510 1.0515 1.0515 4 1.0524 1.0525 1.0525 1.0525 : 1.0550 1.0550 1.0550 1.0550 5 1.0508 1.0508 1.0509 1.0509 : 1.0510 1.0510 1.0510 1.0515 6 1.0510 1.0510 1.0510 1.0510 : 1.0510 1.0510 1.0510 1.0510 7 1.0515 1.0515 1.0515 1.0511 : 1.0515 1.0515 1.0515 1.0511 8 1.0520 1.0517 1.0520 1.0517 : 1.0520 1.0520 1.0517 1.0517 9 1.0515 1.0515 1.0515 1.0515 : 1.0515 1.0515 1.0515 1.0515 10 1.0520 1.0520 1.0520 1.0520 : 1.0520 1.0520 1.0520 1.0520 11 1.0518 1.0518 1.0518 1.0518 : 1.0518 1.0518 1.0518 1.0518 12 1.0519 1.0519 1.0518 1.0519 3 1.0519 1.0518 1.0519 1.0519 : Ave. 1.0516 1.0516 1.0516 1.0516 : 1.0516 1.0516 1.0516 1.0516 LALW._‘_‘_‘JJ‘JJJ+ ‘AJAJJLJA‘AJAAAAAA f L > L L L L r L L b L i A . ‘ .4 AA .4 A .._.A____ ,IIIIL 5| . 0 51 Table XIV. Effect of Viscolization on the Size of the Fat Globules of Raw and Pasteurized Milk. The Size of the Fat Globules Is Expressed in Microns. Pounds Pressure of Viscolization Lot Pounds Pressure of Viscolization QQA;JJJA4LAA‘A_41AJ_AAA 50... A Q a I All 50101 A is 411590. A if -2590 0 500 :1 A A .1590; a i A 25001 41 3 5.95 2.85 2.14 1.45 : 5.95 2.50 1.78 1.45 5.95 2.85 2.14 1.45 : 5.95 2.85 1.78 1.45 5.64 2.85 2.14 1.49 : 5.64 2.55 1.78 1.45 5.57 2.50 1.78 1.42 : 5.57 2.14 1.78 1.45 5.57 2.50 1.78 1.42 z 5.57 2.14 1.96 1.25~ 5.57 2.68 2.14 1.42 : 5.57 2.68 2.14 1.25 5.00 5.05 2.50 1.56 : 5.00 2.85 2.14 . 1.42 5.89 2.51 2.09 1.46 : 5.89 2.50 1.91 1.58 AAAA‘FA—‘444AAAJ‘LLAWAA“AAAJAJJ— 52 Elation 10f Viagoli zed milk Since most of the experimental work in this study was carried out on raw and pasteurized milk before and immediately after viscolization and of viscolized pasteurized milk in storage, any off flavors due to viscolization were not observed until later, when an off flavor in stored raw viscolized milk was called to our'attention. Special work was, there— fore, carried out on this phase of the subject. Results in Table XV show conclusively that viscolization of raw milk at 2500 pounds always developed a rancid flavor within two hours after viscolization. In some samples the rancidity developed much more rapidly than in others. However, at the end of six hours most of the viscolized milk was unfit for human consumption. The unviscolized check samples held at low temperature for five days de- veloped a rancid flavor only in four of 27 trials. Results of two samples of raw milk viscolized at different pressures indicate that the rancidity develops in proportion to the pressure used. However, at the end of 24 hours all of the raw viscolized samples were un— fit for human consumption. Viscolization of separated milk re-standardized to the original fat content indicates that the rancidity develops at the same rate as that of the same milk viscolized without separation. This is shown in Table XVI. Pasteurization of the milk at 145° F. for 50 minutes before viscolization prevents the deve10pment of rancid flavors. The results in.Table XVI also show that viscolized skim milk does not develop rancidity. From this we might conclude that fat must be present before a rancid off flavor due to viscolization develops. Viscolization appears to have little, if any, effect upon the natural flavor of the pasteurized milk. Table XV}. Effect of Viscolization at 2500 Pounds Pressure on the Flavor 0 f Raw Milk Herd LA‘URaw MilkAilar.llliii g_‘Viscolized Milk if- _ A __ Roll ii liglliours a 5 daxslr a - All 2 shameless landhours A ll 15 _ _ ** aaa 51 _ * ** *** 24 _ * * * ** 16 _ - *% *** 5 - * -** -*** 22 _ _ * *%* 25 - - ** *** 15 _ - ** *** 21 - _ ** '*** 17 _ - ** *** 26 _ - ** '*** 62 - _ as. -*** 51 - - ** ‘*** 25 _ * ** -*** 10 - — * '** 7 _ _ ** *** 12 . - - ** *** 2 _ - * ** 5 .. - «res *x- 15 _ _ ** *** 5 _ - ** *** 4 _ - * ** 11 _ - ** *** 5 _ _ ** '*** 59 - - **- *** so _ _ '** -*** 56 - - * '** - no off flavor * approximately 19 score on flavor ** approximately 15 score on flavor *** approximately 0 score on flavor 54 .1 xafle macaw o hampwsaxosdmw *** xHHs whoom ma hampwaHXOHQQw ** Mafia whoom ma mHmpwswaHQmw * Ao>mam mmo e: I xHfiE 3mm *** *** *** I u ** ** * I u * * I I wmmwwhwwcmpm ma * w I I u w I I I u I I I I .momea cmpwmzmsm ma I I I I u I I I I u I I I I .m owed .pmwm NH I I I I u I I I I u I I I I .m com Mafia aflxm ma I I I I u I I I II n I I I I .m oom MAME sfixm NH *** *** *** I u ** ** * I u * * I I .m oom sum ma ask. *** *** I » *** ** * I u * * I I .h com Sam NH I I1 odww. I 83 I II I don I I I Q IIuI II 08% I 83 com- I1 0 I” 8an I 83 J I odMI II I @Iwwlndwmmaflawegidz definesHHooma>detwudmmmmemdedomuumwwmwfiaeomw> mo muwmwmpm meadomwGOHpmmHHoowwswwo dewwmnmemqmmMI no son mason em u mason m » maden m endpwsmdsme 11111.1 1 1 J 4 14111 111 ‘4‘] 5:2 Sam Sam as 55.5 sea so: emaaenaegapm ad: 5m as :39 mafia emfismpmam $32 Bose seasoned :52 5% 5m 3:5 floss Ema no 35E 23 so compaflaoomg .8 585m, .HE mafia I IIIIII I'Il 1 55 Cprd»Tensiopflpfgyisgeligeggyfigg; Although the study of the curd tension of viscolized milk was orig- inally planned for the experiment, equipment was not available until most of the experimental work had been completed. Therefore, the data obtained are not sufficient to show definite conclusions. The results in.Table XVII indicate that the curd tension of both raw and pasteurized milk is lowered in proportion to the pressure of viscolization. However, viscolization of the skim milk showed no change in curd tension. The results in Table XVIII show the curd tension of raw unviscolized and viscolized milk from herds of different patrons who deliver milk to the College Creamery. All the milk was processed at 900 F. using 2500 pounds pressure. The average of 11 trials indicates that the curd tension was re- duced approximately 40 per cent by viscolization at 2500 pounds pressure. Individual samples varied greatly, one sample showed no reduction while ans other showed a reduction of 62 per cent. However, it is interesting to note that the sample which showed no reduction was slightly sour, which may have had some effect upon the change in the curd tension. 57 Table XVII. Effect of Viscolization at Different Pressures on the Curd Tension of Raw, Pasteurized and Skim Milk.** 0 H444#AJ#4A4MAW4JJAA—‘AL—A‘AJAJAAAAAJAAAA—‘LLW#J#AJJA4J44 LAALAAHHI#_A qugds Pressure of Viscolizatiog Temperature of Viscolizatiog o 500 1500 2500 55,99“ Raw 90° F. 57 27 25 12.5 7 Pasteurized 145°F. so 24 8 Skim 90° F. 58 44 39 59 LHLL‘A“AJ_‘_—AAL_‘AAAA‘AA‘4A44L‘ 4AA- k—A—AAAJJLAA‘A AAA—4A4H4AAAAAA—LA AA-h _— ** headings expressed in grams. Table XVIII. Effect of Viscolization at 2500 Pounds Pressure on the Curd Tension of Raw Milk from Different Herds.** Ah AAAAA‘AJJALA~A¥AL4_LALL#LAAAAAL_A AAAAAAAJ‘AMA4ALAA #4444‘44444—L4‘MA4L Herd No. Unviscolized Viscolized 15 50 26 51 51 16 24 50 50* 16 48 55 5 55 57 22 56 17 21 52 40 17 41 16 25 59 52 26 28 8 61 55 17 Ave. 45 26.7 ._A..‘ ‘A4AAkAAA#;;A_‘AAAAL_A_4..AA‘A4A4A44‘4. AA4A4-A4+‘;;AA_‘_A_‘A4AA_AAAJ_A_ * Sample sour to taste. ** Readings Expressed in grams. 59 DISCUSSION Viscolized milk does not form a cream layer providing the pressure of viscolization is 1500 pounds or higher. However, this applies only to the viscolizer used. Other machines of slightly different construction or perhaps machines of the same construction might be expected to give con- siderable different results. In milk viscolized at 1500 pounds pressure the globules were broken down to an average of about two microns in diam- eter while those at 500 pounds pressure were about 2.5 to 2.75 microns in diameter. From this it might be concluded that the pressure of viscoliza- tion must be sufficiently high to reduce the globules to an average diam- eter of two microns or smaller. The reason viscolized milk does not cream is not clearly understood. Numerous instances are cited in the literature stating that the fat in vis- colized milk is not clumped. In studying the size of the fat globules some clumping was observed. However, these clumps were small and few in number, each consisting of not more than 10 or 15 small globules. It is also known that no cream layer forms on viscolized cream although clumps of fat are al— ways present. This would indicate that the small number of fat clumps would have no effect on creaming. The slight creaming on milk viscolized at 500 pounds is in all probabilities due to the rise of the larger fat globules, while in the milk viscolized at higher pressures the globules are so finely divided that they fail to rise by the force of gravity. The fact that the milk viscolized at the lower pressure continues to increase in creaming even after 24 hours indicates that these larger single fat globules, which rise very slowly, may account for this increase. 60 The consumer has in the past judged the richness of the milk by the volume of cream at the top of the milk bottle. Because of the absence of a cream layer on viscolized milk, many consumers have asserted that the fat standards were not observed by the dealers. Health laboratories in a few caseshave found the fat in viscolized milk below the legal standards as shown by the Babcock fat test. The dealers have claimed that the fat globules are so finely divided that all the fat cannot be raised in the fat column of the Babcock test bottles. The results of this study indicate that the Babcock fat test is a reliable index to the fat content of viscolized milk. This study also shows that the average size of the fat globules viscolized at high pressures are between one and two microns in diameter. According to the Associates of Rogers (54) 52.8 per cent of the fat globules in normal milk are of less than two microns in diameter. While these small globules amount to less than two per cent of the total fat content, it follows that the majority of these small fat globules must be included in the fat column of the Babcock test or this test would vary considerably from that of the ether extract tests. The average viscosity of raw viscolized milk appears to be increased by viscolization as the pressure increased although individual samples were irregularly affected. Pasteurization of the milk before viscolization low- ered the viscosity in every case. The average shows a decrease as the pressure increases, but individual samples were also irregularly affected, although always lower than the pasteurized unviscolized samples. The in- crease in viscosity of raw milk may be accounted for by greater adsorption of the milk serum on the greatly increased fat surface. However, the low- 61 ering of the viscosity of viscolized pasteurized milk is rather difficult to explain, but it might be accounted for by the dehydrating effect of pasteurization on the milk protein. The average of the 11 samples shows a slight increase in viscosity of viscolized raw and pasteurized milk after aging for 24 hours. However, individual samples were affected ir- regularly. This increase in viscosity during aging may be due to either increased adsorption or hydration of the protein. 2 The titratable acidity of raw milk is always increased by viscoliza-4 tion, but pasteurized milk shows no such change. Preheating the milk to 145° F. before viscolization prohibited all acidity changes. Pasteuriza- tion of the raw milk after viscolization did not eliminate the acidity changes, although the titratable acidity of this milk during aging did not increase as it did in the viscolized raw milk. Viscolization of the raw skim milk did not increase the titratable acidity. Is the acidity increased a rancid flavor also appeared after a few hours in all the viscolized raw milk examined. However, no rancidity de- veloped in viscolized raw skim milk or milk pasteurized before viscoliza— tion. Preheating the milk to 145° F. before viscolization retarded the rancidity development greatly. Dorner and Widner (70) attributed the increase in titratable acidity and rancidity to‘a lipase. This agrees with the results of Nair (65) who determined the presence of lipase in.milk by an increase of titratable acidity of a high butterfat cream preserved with sucrose. Pasteurization of the milk destroys the lipase enzyme. Therefore, it appears as though the lipase releases the fatty acids of the butterfat thereby not only in- creasing the titratable acidity but also causing a very rancid flavor to appear in the milk. 62 Viscolization of raw milk always lowered the surface tension, while milk pasteurized before viscolization, in general, increased the surface tension slightly. Aging the samples decreased the average surface tension in both pasteurized and unpasteurized samples. However, individual samples were irregularly affected with the exception of the raw milk viscolized at 1500 and 2500 pounds pressure. These were always lowered. The lowering of the surface tension of viscolized raw milk and in- creasing of the surface tension on milk pasteurized prior to viscoliza— tion is difficult to explain. However, it appears that the release of fatty acids by the enzyme lipase would lower the surface tension in visco- lized milk but this does not account for the fact that nine of the 12 trials show the lowest surface tension at 1500 pounds pressure. Increase of the surface tension of milk pasteurized before viscolization might be accounted for by the increased adsorption of the milk serum on the greatly increased fat surface, along with a dehydration of the protein. This would leave more free water which would increase the surface tension. The foaming ability of the raw milk was always lowered by viscolization. Pasteurization of the milk before viscolization appeared to increase the foaming ability. In like manner viscolization decreased the surface tension of raw milk and increased the surface tension of pasteurized milk. However, the highest pressures used did not necessarily give the lowest foaming ability or lowest surface tension with raw milk. The average of 12 trials shows the lowest surface tension and lowest foaming to be at 1500 pounds pressure, al- though both were somewhat irregularly affected. The average for the pasteur- ized milk shows a gradual increase of'both surface tension and foaming as the pressure increased. 65 The larger air cells in the raw viscolized milk may be accounted for by the lower surface tension of the film surrounding the air pockets. In like manner the lower surface tension does not permit the withdrawal of the film surrounding the air cell. This gives greater stability. In the milk pasteurized before viscolization the air cells are much smaller due to the higher surface tension, which tends to give the greatest curva— ture possible to the surrounding film. This greater stress on the film hastens the coalescence of the air cells by the withdrawal of the film. For this reason the foam falls rapidly. As was expected, viscolization has no effect on the specific grav- ity of whole milk. Slight variations in the specific gravity may be ac— counted for by the incorporation of air or by minute changes in temperature. The proteins of milk were always rendered less stable to 95 per cent alcohol by viscolization. As the pressure of viscolization increases the viscolized milk becomes as a rule less stable but its effect is far less marked in milk pasteurized prior to viscolization. Since the total area of the fat phase is increased greatly by viscolization, it is logical to conclude that more of the milk serum would be adsorbed upon the fat phase. It is well known that the addition of calcium salts decrease protein sta— bility, whereas citrates and phosphates increase the stability. This is in accord with the suggestion of Tracy and Ruehe (65) who stated that the destabilizing effect of homogenization may be due to the adsorption of citrates and phosphates at the fat-serum interface. This leaves less of these salts in the serum proper. However, the increase in acidity due to viscolization of the raw milk may also change the relationship between the calcium salts and the citrates and phosphates. This may, in part, account . I} IO’ 1 ,. fl. . 64 for the decreased stability of the raw viscolized milk. Since no acid- ity change occurred in the pasteurized milk, greater stability of the protein would be expected. 65 CONCLUSIONS 1. Pressure of viscolization must be at least 1500 pounds to prevent creaming. 2. The average size of the fat globules must be less than two microns in diameter to prevent creaming. I 5. The Babcock test appears to be as reliable for determining the fat content of viscolized milk as of unviscolized milk. 4. The viscosity of raw milk viscolized at 900 F. appears to be increased as the pressure is increased. 5. fasteurization of milk before viscolization at 1450 F. always decreased the viscosity but not always in proportion to the pressure used. 6. Aging of viscolized milk appears to increase the viscosity. 7. Viscolization of milk at 900 F. always lowers the surface ten, sion, while pasteurizing of milk before viscolizing at 1450 F. appears to increase the surface tension. 8. There appears to be an inverse relationship between viscosity and surface tension. 9. Viscolization of raw milk at 90° F. always lowers the foaming ability, while pasteurization before viscolization at 1450 F. appears to increase the foaming ability. 10. There seems to be a direct relationship between surface tension and foaming ability. .IuIl-vk... II: I 66 ll. The titratable acidity of raw milk is always raised by visco- lization. Pasteurizing the milk before viscolization shows no such change. The titratable acidity of raw milk is increased only if fat is present. 12. Viscolization of raw milk always causes a rancid flavor to ap- pear within a few hours. This appears to be caused by a lipase. 15. The specific gravity of milk is not affected by viscolization. 14. The proteins of milk are always rendered less stable to alcohol by viscolization. As the pressure of viscolization increases the pro-‘ teins as a rule become less stable but this effect is far less marked in the pasteurized milk. 15. The curd tension of both raw and pasteurized milk appears to be decreased in proportion to the viscolization pressure, if fat is present. l. ‘2. '80 9. IO. 67 LITERATURE CITED Turnbow, G. D. and L. A. Raffetto 1928 Ice Cream. ix plus 407, illus. John Wiley & Sons, Inc. New York. Sommer, H. H. 1952 The Theory and Practice of Ice Cream Making. vii plus 611, illus. Author, Madison, his. Jones, W. F. 1929 Dispersed Cream Lines Tell No Tales Milk Dealer 18(9):1S4. Hollingsworth, J. B. 1951 Homogenized Market Milk - How It Is Increasing Consumption in Canada. Milk Dealer 20(9):65. Hammer, B. W. 1916 Studies on the Creaming Ability of Milk Iowa Agr. Expt. Sta. Res. Bul. 31. Martin, W. H. and n. 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