510 THE JOURNAL OF INDUSTRIAL AND ENGINEERING CHEMISTRY Vol. 13, No. 6 Precipitation of Grain-Curd Casein from Pasteurized Milk, Including Sweet Cream Buttermilk'tz By Harper F. Zoller

DAIRY DIVISION, BUREAUOF ANIMALINDUSTRY, u. s. DEPARTMENT OF AGRICULTURE,WASHINGTON, D. C. TABLEI The application of the normal grain-curd method to ______R dm. the manufacture of casein from milk, which has some- Temp. of gression ' Heating Time Per cent of Nature of time during its history been heated to pasteurizing Portion ' C. Min. Ash H+ Ion Curd A 50 60 3.80 Yes Soft temperatures or higher, cannot be made without certain B 63 60 4.28 Yes Soft. featherv C 80 60 4.84 Yes Very soft, fine and dark modifications. D 98 30 5.21 Yes Very soft,fine and dark It was found throughout the experimental study of E Unheated control 2.02 No Firm and normal the separation of casein from pasteurized milks that a few minutes from the time the curd was suspended when the identical conditions of the grain-curd pre- in the wash water (at pH 4.6) the pH of the supernatant cipitation were observed the resulting casein was of a water had increased to 5.6. The change in pH decidedly different texture from the normal type of could be followed quite accurately with methyl curd from unheated milk. The curd was softer, and red. It must be remembered that the curd had just the grains were less definitely formed and much smaller been taken from its whey which registered a pH of in size. Changing the velocity of stirring during the 4.6 to methyl red. From hydrogen-electrode measure- precipitation had no appreciable effect upon this ments' it is found that when methyl red registers a peculiar physical texture. It was found that this pH of 4.6 in skim milk the actual concentration of curd could not be economically handled upon the hydrogen ion is greater (pH 4.1 to 4.20) than that de- drain rack. Clogging of the pores of the cloth re- manded by the isoelectric point of casein. Hence this sulted, rendering rapid draining of the whey impossible. retrogression of the hydrogen ion in the wash water Working of the curd upon the cloth caused many fine is even more astonishing. This was further magni- particles to pass through the pores, while that which fied when it was found that the retrogression occurred remained upon the cloth became soggy and puddled. even after as many as ten-changes of wash water, Furthermore, an additional phenomenon was ex- although in these instances with protracted washings perienced during the washing of the curd. When the the curd began to disperse rapidly in the medium. curd was leached with water adjusted with hydro- This dispersion of the curd in the wash water is, again, chloric acid to the isoelectric condition of casein, i. e., contrary to the experiences with normal grain curd. pH 4.6, there was a marked retrogression of the hy- INFLUENCE OF TIME, AT CONSTANT TEMPERATURE, drogen ion. This phenomenon throws some light on UPON PHYSICAL NATURE OF CURD the influence of heat upon the protein andsalt equi- Like quantities of fresh skim milk were placed in librium in milk. The discussion of this question is shotgun milk cans, and these were set in a large vat reserved for a later paper. of water heated to 63" to 64" C. and maintained at Some of the experimental procedures aimed towards this temperature throughout the experiment. The the restoration of the normal texture to the curd will milk was thoroughly stirred in each can during the now be reviewed. heating. When the period of heating was over each INFLUENCE OF DIFFERENT PASTEURIZING TEMPERATURES can, in turn, was plunged immediately into running UPON NATURE OF CURD water at 18" C. The casein was precipitated under exactly the same Twenty-five-pound portions of fresh skimmed milk conditions as in the above experiments. The results were separately heated to the temperatures indicated are given in Table 11. in Table I. After cooling to 34" C., the casein was TARLEI1 precipitated ,with normal hydrochloric acid, using Retro- Milk Temp, of Time OF gression methyl red as indicator of the end-point as in the regu- Portion Heating Heating of lar grain-curd method.3 The curd was then thrown C. Min. Hf Ion Nature of Curd A 63 20 ' Yes Softer than control upon a cloth in a drain rack and allowed to drain free B 63 40 Yes Too soft to wash C 63 60 Yes Feathery from whey. Tap water adjusted to pH 4.6 was put D 63 90 Yes Very soft, and disperses in whey into a vat large enough to accommodate the drained E Unheated . . No Firm and normal curd. The edges of the drain cloth were gathered It is evident that the duration of heating has nearly together, and the curd was lifted from the tray and as much effect upon the nature of the resulting curd immersed in the wash water for a period of 10 rnin. as the degree of heating. It has been shown, however, When possible, the curd was agitated in the water so that it does not have quite the same effect upon the that the washing would be as thorough as possible. equilibrium of milk salts.2 The washing process was repeated in three changes RESTORATION OF FIRMNESS TO THE CURD BY USE OF of adjusted water. DIFFERENT ACIDS FOR PRECIPITATION The retrogression of the hydrogen ion was marked Before proceeding with the influence of the various in these experiments, especially in B, C, and D. Within anions of acids upon the firming of the casein curd 1 Received January 26, 1921. 1 W. M. Clark, H. F. Zoller, A. 0. Dahlberg and A. W. Weimar, Tms 2 Published with the permission of the Secretary of Agriculture. JOURNAL, 12 (1920), 1163. 8 THISJOURNAL, 12 (1920), 1163. 2 Unpublished results. June, 1921 THE JOURNAL OF INDUSTRIAL AND ENGINEERING CHEMISTRY 511 lrom heated milks, attention should be called to another USE OF COPRECIPITANTS WITY H,YDROCHLORIC ACID IN possible factor in the acid precipitation of the casein. PRECIPITATING CASEIN This idea is not original, since Lacquer and Sackurl The coprecipitants which would be suggested by found that casein which had been dried at high tem- the work of Freundlich,l Linder and Picton,2 Hardy,8 peratures suffered “cleavage,” and the alkali-soluble and others would be those possessing polyvalent portion, which they designated as “isocasein,” possessed cations, This is because it has repeatedly been demon- an increased base-binding capacity over normal casein. strated that casein exists in ordinary milk in the form From their conductivity measurements they arrived of a caseinate anion possessing a charge equivalent to at the conclusion that this body was a much stronger a tetra-, hexa , or octabasic acid (or multiple thereof). acid than ordinary casein and consequently possessed Hence as this charge becomes neutralized by positive a greater dissociation constant. hydrogen ion, as it does in acid precipitation, the casein With a set of buffer mixtures covering the probable finally reaches a point where its electrical charges are range of Hf-ion concentration in which the isoelectric equivalent, or zero in external effect (the isoelectric point would be found, and a 0.1 per cent solution of point), and in this state is extremely sensitive, as a sodium caseinate at pH 7.2 made from the curd from neutral colloid, to physical stimuli. Thus we should milk heated to 80” C. for 1 hr., the writer was unable expect those electrolytes which affect pure suspensoids to note any marked displacement in the probable iso- to affect similarly this neutrally suspended casein. electric point. The idea was to note the pH zone in Investigations by the above-mentioned workers have which the casein precipitated. Of course, this method shown that polyvalent cations produce maximum is very rough, and a more elaborate study should be effects upon such colloids and form firm coagula or made of this question. precipitates. Further it has been shown that these In the manufacture of casein by the grain-curd electrolytes, or “coprecipitants,” as they are termed process in the factory the writer frequently noticed in this paper, usually contaminate the precipitate, that when the skim milk was slightly sour from lactic which leads to the speculation that the mechanism of acid fermentation the resulting casein curd was ex- this phenomenon is one of adsorption. tremely firm and excellent to handle. Repeated The polyvalent cation salts available (readily) at trials in the laboratory confirmed this experience. this time were those of aluminium and the alums. Solutions of the following acids were prepared in normal Solutions of 0.2 M aluminium sulfate, ammonium concentration with respect to the hydrogen ion: alum, and potassium alum were prepared. These lactic, citric, oxalic, tartaric, acetic, phosphoric, solutions were strongly acid in themselves (pH 2.1 sulfuric, nitric, and hydrochloric. Two volumes of the to 2.4) and served to precipitate the casein alone without normal acid were mixed with one volume of normal the addition of further acid, but the addition of so hydrochloric acid, and the mixtures were used as the much extraneous salt was inadvisable. Ash analysis precipitants in fresh skim milk pasteurized at of some of the caseins prepared with aluminium sulfate 63’ C. for 1 hr. The casein was precipitated at 34” C. as the sole precipitant showed as much as 8.5 per cent under the control of methyl red. The physical nature ash. of the curd was carefully noted. The results appear The precipitation mixture which yielded an average in Table 111. curd from heated milks consisted of one volume of

TABLEI11 M alum solution with two volumes of N HCl. When Temp. of Retrogression the regular grain-curd process was followed with this Acid + HC1 Precipitation of H+ precipitant on milk heated to 80’ C. for 1 hr., the re- 2 Vols.: 1 VOl. c. Ion Character of Curd Lactic 34 No uite firm and washable but sulting curd was fairly firm, could be washed quite well, * short (brittle) but was very brittle. The caseins resulting from this Citric NO 34 Quite firm and washable but short (brittle) treatment ashed from 4.5 to 5.5 per cent of mineral Oxalic 34 Slight Not as firm as lactic Tartaric 34 No Quite firm and washable (brittle) matter. Acetic 34 Very slight Curd washable but brittle Phosphoric 34 Yes Soft and disperses Sulfuric 34 Yes Soft and disperses EFFECT OF HIGHER PRECIPITATION TENPERATURES Nitric 34 Yes Firmer but not washable Hydrochloric 34 Yes Soft and disperses UPON TEXTURE OB CASEIN CURD It was evident during the early studies that the tem- There is a marked influence upon the physical peratures of precipitation had a marked influence structure of the casein curd which suggests, aside from upon the cohesion of the curd particles. In following any practical application, a relation to Pauli’s2 the effect of temperature upon the precipitation of and Batschek’s3 work on the production of a stiffer grain-curd casein from fresh, unheated skim milk, the gel with gelatin or agar by the addition of citrate or extreme sensitiveness of the coagula to slight changes tartrate. This effect is undoubtedly a manifestation in the temperature of the medium which bathed them of a change in the distribution of water between the was duly appreciated. Accurate colztrol of the precipi- two phases. Whether we consider this change to be tation temperature is one of the main factors in the success wrought by the resulting concentration of hydrogen of the grain-curd method. ion or by the distribution of electrical charges, or what Now when the milk has been subjected to abnormally not, such considerations have no place in this paper. high temperatures for varying lengths of time, the pro-

1 Beilr. chem. physiol. pathol., 3 (1902), 210. 12,physik. Chem., 44 (1903), 129; Z. Chem. Id.Kolloide, 1 (1907), 321. 2 Arch. ges. Physiol.. T8 (1899), 315. 2 J. Chem. SOL,61 (1892), 137. 8 “Introduction to the Physics and Chemistry of Colloids,” 1916, p 49. a Proc. Roy. Soc. London, 66 (1900). 110; J. Physzol., 38 (19Q5), 281. 512 THE JOURNAL OF INDUSTRIAL AND ENGINEERING CHEMISTRY Vol. 13, No. 6

teins are believed to become denatured. That is, above conditions of the experiment. The temperature during the heating the physical properties of the pro- of 42.5" yielded by far the best curd in this series. teins are changed in such a manner that the molecules EXPERIMENT B have an abnormal absorption affinity for water. This A series of experiments were designed to determine is .a progressive process, as a glance at Table IV will the effect of the duration of heating upon the optimum show. precipitating temperature, when the pasteurizing TABLEIVI temperature was held constant. The pasteurizing Temp. of Time of Temp. of Moisture Heating Heating Precipitation in Curd temperature was 63 ', probably representing the one Milk c. Min. O c. Per cent A ...... 50 60 34 44.6 most commonly used. Time periods of 20, 30, 40, B ...... 63 60 34 62.2 60, 80, and 100 min. were studied. The results of c...... 75 GO 34 68.5 D ...... 100 30 34 79.4 these studies are shown graphically in Fig. 1. The E ...... 120 15 34 88.2 F...... Control .. 34 40.3 grain-curd principle of precipitation was observed in 1 The data in this table were determined by treating the above milks as in the grain-curd method, draining as free from whey as possible, and all save the temperature. The optimum precipitating washing once by decantation with equivalent amounts of water. The temperature was defined as that temperature which curd was then thrown upon a drain cloth and allowed to drain for 30 min. The moisture content of these curds was then determined by drying about produced a curd that most nearly simulated grain curd 5-g. portions in an oven at 98' to 99' C. to constant weight. The moisture content is expressed in per cent. in its uniformity of size and condition for washing. The higher the temperature the greater amount of Another series of tests were performed upon milks pasteurized at different temperatures, in order to de- water will the curd hold, until at excessive temperatures the phase approaches a reversal and the curd simulates a gel in appearance.' This water-holding power of the curd must be in some degree a reversible process, because when it is precipitated in a medium heated to temperatures in the neighborhood of those used in pasteurizing, the curd becomes firm again, although its internal structure is still abnormal. Some of the following observations will serve to emphasize the importance of higher precipitation temperatures with heated milk. EXPERIMENT A FIG. CONSTANT TEMPSRATURE,FIG. Z-CONSTANT TIME OF PAS- Fresh skim milk was pasteurized at 63' C. for 1 63' C. TEURIZATION,60 MIN. hr. It was then cooled down to the temperatures indicated in Table V and the casein precipitated there- termine the optimum temperature for obtaining a from with normal HC1, using methyl red to indicate workable curd from each milk in question. With the approach to the isoelectric point. The curd was the exception of the temperature, the grain-curd method then drained from the whey and suspended in adjusted of precipitation was followed throughout. The time water (pH 4.8). of pasteurization of the milks was held constant TABLFV (1 hr.). The results of these tests are reproduced in Temp. of Retro- Ash the optimum temperature curve in Fig. 2. Precipi- gression in tation of Casein This effect of precipitation temperature is obviously Milk C. H+Ion Texture of Curd Washable Per cent A 30 Yes Feathery No 2.88 of immense importance, and its practical application B 35 Yes Soft No 3.14 C 40 Slight Firmer and grained Not readily 3.92 is at once evident. Further discussion of it is reserved D 50 No Chunks Yes, but imper- 4.20 fectly till later in this paper. E 60 No Large clumps, Yes, but imper- 4.16 leathery fectly EMPLOYMENT OF RENNIN IN PRECIPITATION OF CASEIN F 42.5 No Very firm and Yes 3.85 PROM PASTEURIZED MILK grained Without permitting himself to become bewildered It was noticed during- the washing- of the curd, with the diverse considerations upon the mechanism precipitated at 40' C., with cold water that brittle- of rennin action in normal and heated milk, the writer ness was increased, whereas if the wash water was decided to determine the practicability of this method warmed to about 30" to 35' the brittleness was not for the separation of casein from pasteurized milk, so noticeable. The toughness of the curd, which is including buttermilk. a result of the higher temperature of precipitation, Fresh skim milk, which had been pasteurized at remains unchanged in the warm wash water. All of 65' C. for 1 hr.,was carefully adjusted to the zone of the curds, such as C and D, which approximated normal the optimum activity of rennin in heated milk (about grain curd in appearance were found to be very "short" pH 6.2) 1 with hydrochloric acid, using bromocresol in texture. This is a characteristic property of all purple to determine the pH. The milk was then cooled pasteurized milk caseins. to 37' C. and the usual amount of rennin added. The The essential fact divulged in Table V is that differ- clotted curd, after cutting, was digested in the whey ent precipitating temperatures influence the physical for half an hour at 60' C. to expel moisture and salts. nature of the curd from milk pasteurized under the It was then drained upon a cloth in a drain rack and 1 It should be mentioned that since the writing of this paper Mr. Leighton of these laboratories has actually obtained a curd gel by heating washed several times with water. After pressing, it milk at high temperature (about 140° C.) in a sealed bomb. 1 Biochem. J., 9 (1915), 215. June, 1921 THE JOURNAL OF INDUSTRIAL AND ENGINEERING CHEMISTRY 513 was ground and dried like ordinary casein, and finally because of the effect of the absorbed precipitant upon analyzed. It was found to contain 9.5 per cent mois- the ash content of the resulting casein. The hiqh and ture and 5.8 per cent of ash. insoluble ash reduces its solubility in alkalies. An explanation of the high digestion temperature Certainly the simplest way to render the casein used above is necessary at this point. It was found from pasteurized milk obtainable under factory working after cutting the curd that it was very soft and mushy, conditions is to increase the temperature of precipita- and remained in this condition until the temperature tion, as the results of the studies on this factor was raised above that ordinarily used in jirming rennin indicate. It is the easiest factor to control in factory curd from unheated milk. It was uniformly found practice. In the time-worn commercial methods of that pasteurized milk required a higher temperature precipitating casein, high temperatures were universally for the firming of the curd, at the same time-interval employed, viz., 45’ C. and up. It is immediately and acidity, than is necessary for unpasteurized milk. evident why little troztble was met in precipitating casein This corroborates the temperature effect upon the from heated milks in the past. With the grain-curd casein curd discovered in connection with acid pre- method this question is of the utmost importance. As cipitation. Members of the dairy manufacturing previously mentioned, the curd at the isoelectric section inform the writer that in their work with pas- point is in an extremely sensitive condition and re- teurized cheese greater heat has always been found sponds in a maximum degree to physical stimuli. The necessary to firm the curd from pasteurized milk. temperature of 34 ’ to 35 ’C. is the narrow zone for opti- Obviously, the time required for this method and the mum working condition for grain curd from normal vat space necessary would alone mitigate against its milk. This temperature is much too low for the opti- practical use. The character of the final casein is mum working curd from pasteurized milk. not greatly different from the acid-precipitated casein The modified scheme of the grain-curd process to from heated milk, except that it contains higher ash. be applied to heated milks in factory practice is as This high ash content naturally results from the fact follows. that it enmeshes large quantities of insoluble calcium OUTLINE OF METHOD FOR MANUFACTURE OF CASEIN and magnesium phosphates which remain insoluble FROM PASTEURIZED MILK at the reaction in the pH zone in which rennin coagula- tion takes place. The writer finds that both calcium Essentially this is a modification of the grain-curd and magnesium phosphates (CaHP04 and MgHP04) method described by Clark, Zoller, Dahlberg and are practically insoluble at this reaction, namely, Weimar.’ pH 6.2. (1) The milk should be heated to a temperature in- Another disadvantage of this rennin casein is its dicated upon the published curves that correspond to slow rate of dissolving in alkalies. In this respect it the pasteurizing conditions to which the milk was sub- is not unlike cooked curd casein which it also resembles jected. If the history of the milk is not known the in ash content. If the engulfed salts could be removed optimum temperature may best be determined by from both of these caseins it would increase their rate trial. of solubility. This was actually found to be the case. (2) Dilute hydrochloric acid (100 lbs. of 20’ Bi.. The caseins were redissolved in dilute ammonia, the to 800 lbs. of water) should be added slowly to the undissolved residue separated by centrifuging at great heated milk, bringing it into contact with all portions speed, and the resulting solution precipitated with of the milk as quickly as possible. A hardwood vat dilute acetic acid, and thoroughly washed. The and spigot (hardwood) prove to be the best containers resulting casein curd was still characteristic of high for the dilute acid in factory practice. When the milk temperature caseins in “shortness,” but the dried ‘(breaks,” i. e., when the curd first separates from the product dissolved more readily. The nonvolatile whey, the flow of acid should be checked and the pH ash amounted to less than 1.6 per cent in both cases, of the whey determined with methyl red indicator (5 drops of a 0.04 per cent solution of methyl red in DISCUSSION OF EXPERIMENTAL RESULTS 10 cc. of milk or whey). It is frequently noticed that It is evident from the temperature and time studies in pasteurized milks the “break” is considerably de- that the condition of the casein in pasteurized milks layed. This makes it very easy to overstep the end- varies with the conditions of pasteurization and, there.. point. The addition of acid should be ceased when the fore, it is necessary to take these factors into considera- indicator first shows a bright red. tion when attempting to prepare casein from such (3) The whey is then drained from the curd. Be- milks. cause of the delayed “break” it is frequently impossible While the organic acids are found to yield a good to draw off a portion of the whey before adding the working curd, they would be impracticable industrially remainder of the acid necessary to reach the end- because of the cost. It would be possible to consider point. Wherever this is possible the reader is referred lactic fermentation (natural-sour process), but this is to the regular method cited above for full details. a very unsanitary method to apply in factory practice. (4) The curd is then washed with water at a tem- In respect to the use of coprecipitants with hydro- perature of about 30” to 35’ C. and adjusted with chloric: acid it may be said that, wcile the alums were hydrochloric acid to pH 4.8. The washing may be done found to increase the firmness of the curd precipitated in the vat by decantation before placing in the drain at grain-curd temperatures (34 ’ C.), thus facilitating rack, or afterwards, as desired, although the former the draining and washing, they are not advocated 1 LOC. Cil. 514 - THE JOURNAL OF INDUSTRIAL AND ENGINEERING CHEMISTRY Vol. 13, No. B

method is somewhat more effective. Drain racks and (1) The operation is entirely mechanical from the screw presses are probably best adapted for very small precipitating vat through to the final washing in the casein plants. Where large quantities of milk are centrifugal bowl with adjusted water. handled, the factory would be repaid by installing a (2) The draining, washing, and pressing of the curd centrifugal which handles both operations in one. The are done in one operation. The curd may be pressed application of the centrifugal is discussed below. to any degree desired by merely varying the speed (5) For the drying of th8 casein and other details of the rotating bowl. It is ready to be ground when the reader is referred to the publication on grain-curd taken from the bowl without further pressing, and is casein mentioned above. ready for the dryer. (3) The saving of considerable time by completing SEPARATION OF CASEIN FROM PASTEURIZED SWEET in one day an operation which now generally demands CREAM BUTTERMILK two by the rack, cloth, and press method. The method just elaborated has been found to work (4) The improvement of the sanitary conditions well with this type of buttermilk. Small-scale factory around the factory by doing away with wooden trays, trials with buttermilk from cream that has been press divider-boards, drain cloths, and press cloths, pasteurized at 63’ C. for 30 min. seemed to show that which now become the eyesore and olfactory press- 40° C. was the desirable precipitating temperature agent of every casein plant using these accoutrements. for satisfactorily handling the resulting curd.1 Cream (5) The main equipment necessary in a large factory pasteurized at the same temperature for 1 hr. demanded would be the precipitating vat, or vats, centrifugal, 45’ for precipitation of the casein from the butter- curd mill, casein drying tunnel, and grinder for the milk, It is remarked that the fat content of the butter- dried casein. milk alters the “feel” of the curd, as well as its working (6) The centrifugal would be especially well suited conditions. But the amount of fat which should con- to the washing and pressing of the casein prepared taminate sweet cream buttermilk is so small as not from pasteurized milk by the modified grain-curd to handicap seriously the use of this method. method, because of the short character and brittle- USE OF CENTRIFUGAL IN MANUFACTURE OF CASEIN ness of the curd. It would receive less handling in The use of centrifugals for washing casein has been the centrifugal and the loss therefore would be less. practiced for many years in those countries where the SUMMARY price of commercial casein is considerably less than it I-The grain-curd method can be successfully ap- is in normal times in the United Statesa2 plied to the separation of casein from pasteurized During the war the’ casein campaign permitted milks only when higher precipitating temperatures the writer to try out in practice centrifugals of fairly are used. The optimum temperatures are exhibited large capacity, It was at once clearly demonstrated in the form of curves for the different observed con- that there was available in grain curd a type of product ditions of pasteurization. especially suited to the centrifuging process. The 11-The marked differences in the physical nature commercial casein curds in the past were either so of the curd from pasteurized and unpasteurized milks bulky and tough or else so soft that even loading of are strikingly revealed by the grain-curd method of the bowl of the centrifugal was impossible. But precipitation. Attempts to overcome some of these with grain curd the particles are so uniform in size physical effects by the use of organic acids as pre- that a case of an overbalanced bowl was never ex- cipitants and with coprecipitants are described. perienced in the number of trials conducted. 111-The advisability of using rennin to precipitate Large sugar centrifugals in three different milk casein from pasteurized milk is dismissed because of product factories were placed at the author’s use for the time required and the large quahtity of mineral study. Through the courteous cooperation of the matter entrained in the curd. employees in the factories mentioned, test runs IV-Large centrifugals are recommended for wash- were made with grain-curd casein. In one test with ing and pressing the casein precipitated by the grain- a machine possessing a 54-in. bowl and bottom dis- curd method from pasteurized and normal milk. charge, the total curd from 5500 lbs. of milk was V-The phenomenon of the retrogression of the accommodated in one load. The time required for hydrogen ion was discovered in the whey and wash the precipitation of the curd, loading it mechanically water from the curd precipitated from pasteurized from the vat into the revolving bowl, whizzing free milk by the grain-curd process at 34’ C. This rapid from excess whey, washing with 2000 lbs. of water, decrease in acidity is attributed to the excessive pre- and pressing free from water for grinding within the cipitation of alkaline earth phosphates during pas- bowl by increased speed of revolution, was only 40 teurization, and their subsequent re-solution at the min. In another half hour it was ground and placed expense of the hydrogen ion as they are brought into upon trays in the tunnel dryer. ready contact by the soft dispersing curd. The advantage of the centrifugal over the drain- VI-The great check in the rate of this retrogression rack, cloth, and press method may be enumerated as wrought by using higher temperatures for precipita- follows: tion is believed to be due to the engulfing of these 1 The writer desires to thank Mr. A. 0. Dahlberg of this Division for precipitated phosphates by the firming of the curd, trying this method on sweet cream buttermilk at the experimental creamery located at Grove City, Pa. thus reducing the intimate contact between the solution 2 “Casein,” 1911. and the phosphates.