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I N D U S T 13 1 A L A N D E N G I N E E 1% I N G CH E M I S TR Y
(3) Surface dust, one of the greatest obstacles to a good oiling job, improved the quality of the oil mat in all soap treatments. CONCLUSIONS FROM SECOND EXPEKIYENTAL ROAD. T O avoid the eventual bad infiuences of the sodium ion on the properties of the soil colloids, potassium soap was used in the second oiling job, which was done in October, 1933, near Urich, Ma. Besides the general results which corresponded to those obtained on the first road, and of the many Iaboratorv test samoles. . . the following observations seem to deserve special mention: (1) In spite of the cool weather at that time the oil-soap emulsion was so well absorbed by the soil that after 3 hours the distributors could travel over the road without nicking up any material or rutting the road surface; on thk other hand, the straiaht oil applications congealed and were not absorbed for several days: (2) Besides this time-saiing element, it seems to be advisable. esneciallv io acid soils. to a n d v the second oil coat as soon as possible after the emulsion-like treatment because I
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intervening rain and traffic may injure the treated surface, especially since some of the soap in the system may have kept its emulsifying properties. This danger can be practically eliminated by determining the amount of the soap to be used, based upon data covering exchange capacity and lime content of the soil. But even if there is an excess of soap, the immediate application of the second coat protects the system. ACKNOWLEDGMENT The author expresses his sincere appreciation to the omcisls of the Missouri State Highway Department for making this study possible, and to the members of the Department of Soils of the University of Missouri for their suggestions and criticisms during the progress of the investigation. (1) Nioholson.
LITERATURE CITED V.. Proc. Assoc. Asphalf Paving Technolowls. 1932.
2848. @) Reageis F.
"., Ibid.. 1932* 93-105.
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R~~~~~~~ . ~ ~14. ~ 1934. i i
Improved Casein Manufacture RICHARDW. SMITH, JR., University of Vermont, Burlington, Vt. KIMhIED milk is the most important by-product of the of milk either by fermentation or the addition of acids must dairy industry, and casein is the most important mate- be conducted under rigidly exact conditions to attain that rial manufactured from it. The process of casein re- cssential end. Most important of these is the control of covery appears to be simplicity itself, but its lack of a p acidity a t precisely the proper point to secure exact precipitaparent complications is the stumbling block of most operators. tion. This point, most accurately measured by pH deterBoth acid additions and natural fermentation of skimmed minations, has been shown by experience to be practically milk are used commercially to coagulate the casein. (For unattainable by batch methods. A second essential is to detailed descriptions of the various methods of casein maou- conduct the precipitation in such a way as to minimize ash. A recently developed continuous process involving several facture heretolore used, see literature citations 4,5, 6.) It is so easy to allow milk to stand and sour or to add to it unique features (3) permits proper control of all the elements just enough acid to cause precipitation that the complexity of in the precipitation and subsequent handling of the casein, the material involved (a protein colloid) and the variations and is producing a product which users have found sufficiently s u p e r i o r t o t h e average possible in the quality of market commodity t o t h e p r o d u c t (commercial justify a premium price. casein) are often overlooked. To understand the sigThe pronounced variations nificance of the new, it will in the product of t h e s e be valuable to review briefly s i m p l e operations simply the older processes and to carried out Cave caused als u m m a r i z e the important most endless trouble to the characteristics of casein itlargest consumers of casein self from a physico-ohemioal -the paper manufacturers point of view. -who use approximately 80 per c e n t of t h e total OLD PROCESSES amount consumed annually Milk normally is slightly in the United States, prinacid (pH about 6.6) and is, cipally to glaze papers for from the point of view of the fine printing demanded casein production, a eolby modern a d v e r t i s i n g . OF MILK FIGURE 1. OLDER BATCHPnOCESS OF ACIDIFICATION loidal suspension of proteins FOE CASEINMANXEMXWW The next largest a m o u n t and albumins in an aqueous p r o b a b l y goes into glues. M u c h hand labor ie required. solution of lactose and cerThere are manv other uses such as cold water paints, leather dressings and finishings, tain mineral salts. The simplest method of recovering the pastes, shoe polish, casein plastics, special food products, casein consists in fermenting the lactose to lactic acid by microorganisms naturally present. For this purpose the medicines, oil cloth, linoleum, soaps, etc. Casein, like many other products, is much less simple than skimmed milk is run into large, relatively shallow, open vats its name indicates. As it occum in milk it is made up of a and held a t a temperature favoring fermentation (about variety of proteinous bodies in intimate mixture. The neces- loo0 F. or 37" (3.). When the acid intensity reaches a p R sity for absolute uniformity in a material so widely used in value of approximately 4.6, sufficient lactic acid will have desuch quantities is paramount. Therefore, the acidification veloped to cause the formation of a desirable curd. This is
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INDUSTRIAL AND ENGINEERING CHEMISTRY
broken up, usually by hand-operated rakes or by heating, and allowed to settle. The whey is drawn off immediately and the curd washed two or three times with water. It is then pressed in hydraulic or hand presses to expel as much moisture as Dossible. The cakes of messed curd are milled. spread on d i y i n g trays, and dried in t u n n e l driers. The final step in the process is the grinding of the dried casein to a fine powder. This method is largely used in the Argentine and produces, strange as i t may seem, a superior grade of casein. Its
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hydrochloric because of the lower solubility of its calcium salt and the consequent difficulty in producing a low ash precipitate.
PHYSICO-CHEMICAL PROPERTIES O F CASEIS’ Casein, in addition to being one of the purest, belongs to the most complex group of proteins, the phospho-proteins. I t contains c a r b o n , oxygen, nitrogen, hydrogen, phosphorus, and sulfur. In milk it exists as a colloidal suspension combined in different proportions with small amounts of calcium. The several other constituents of milk further complicate the situation. In coagulating such a mixture, it is obvious that variations in acidity produce variations in the exact nature of the mixture precipitated. Thus, even a small fraction of one per cent of acid cannot be added to the batch of milk carefully enough to prevent momentary overacidity in part of the mixture and underacidity in other pares. Under these circumstances the overacid portion will -Mic6 precipitate every proteinous compound present and the underacid part will be incompletely coagulated. Because the added acid is not only neutralized but is a t the same time absorbed and adsorbed by the precipitate, subsequent thorough mixing will not entirely correct t’hefault of initial inhomogeneity. Complete precipitation will require an overdose of acid, and the final product will conFIGURE 2. ACID FEEDREGULATOR AXD RfILK ACIDIFIER tain a lnixture of Droteins which cannot be duDlicated accurately except by chance in the making of later principal disadvantages are inherent in the fermentation batches , process itself which consumes time and which yields a curd The precipitated curd, holding within itself more or less occluding various impurities held within the clots themselves. acid, is washed and later pressed to remove as much moisture These impurities are difficult to remove economically or effi- as possible. The washing operation, like the precipitation, is ciently. Batch operation is also disadvantageous from an liable to leave unequal acidity in the pressed curd. During efficiency point of view. the pressing operation, as well as in the subsequent drying of The second method is less tedious and more easily adapted the mass, this residual acid hydrolyzes the casein to a greater to modern production methods. It consists of adding a or less extent depending on its concentration a t various points diluted mineral acid (usually sulfuric but sometimes hydro- in the mass. The heating required during the drying operachloric) to the skimmed milk in large shallow vats, mixing the tion emphasizes rather than minimizes these differences in whole carefully, precipitating the curd, and proceeding as acid concentration so that the finished casein from the final described above. As practiced, all the operations in the grinding retains the characteristics produced in it during these process are carried out by hand as in the cruder fermentation steps in its manufacture. process, and it possesses very much the same drawbacks as Obviously this simple series of steps cannot be made to fermentation, with the exception of the time consumed. yield a material of rigidly uniform properties as required It has this further disadvantage which prevents complete by the paper industry which must produce, practically by the uniformity of the product. In adding a relatively small square mile, paper whose printing characteristics are peramount of acid to a large volume of milk, there are always fectly uniform. To overcome these disadvantages, the procparts of the mix which are a t one time or another more acid ess has been reduced to a continuous operation i’n which each than others. Kot only are there such points of higher acidity, step is accomplished by an unerring machine. The accombut these are never exactly the same in extent or intensity in plishment of this end has involved chemical engineering skill any two batches. Consequently, despite great care on the and ingenuity of a very high order. part of each operator, there will be precipitated in each batch NEW PROCESS of his product some casein containing “foreign” proteins in varying amounts. This lack of uniformity of output and the The major credit for the development and improvement large amount of hand labor involved in the process has always of this new continuous process should be given to F. L. placed the product of this method of acidification a t a dis- Chappell of Hobart, N. Y., dean of America’s casein manuadvantage on the market. Kevertheless, this process is facturers. largely used in the United States and accounts to a great Since control of acidity is the prime factor in the success of extent for the low opinion users ordinarily hold of domestic the process, the acid-mixing chamber is the heart of the casein. plant. Even though the unit itself is small, its proper funcRegardless of the particular process used, all batch methods tioning is fundamental to the entire operation (Figure 2). present certain serious difficulties. However, many im- The small stoneware cylinder contains baffles to secure pracprovements have been made in the various batch methods in tically instantaneous mixing of the ribbon-like streams of recent gears. The most important among these is the so- milk and acid which meet within it. I n this way the actual called grain-curd process developed by the Bureau of Dairy acidification of any particular small volume of milk occurs in Industry of the U. S. Department of Agriculture. If a batch a small fraction of a second, and the baffle arrangement semethod is to be used, the grain-curd process should be the one cures completely uniform mixing of the two streams. NOpart of the milk stream is even for an instant in contact with more selected. Sulfuric acid, although frequently used, is inferior to acid than is required to bring its pH to the desired point.
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Hydrochloric acid (specific gravity 1.20) diluted with four times its volume of water and skimmed milk preheated to 110’ F. (43.5’ C.) meet in the mixer. Complete precipitation of the casein requires a somewhat longer time than the mere mixing operation, so the acidified skimmed milk, after leaving the mixing chamber, runs through a subsequent series of baffles which continue the agitation of the mixture for a few seconds until the curd has partially separated from the whey. This subsequent mixing chamber is an open stoneware tray provided with baffles to force the mixture to travel back and forth on its way to the washers. (All stoneware parts were made by the General Ceramics Company.)
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addition the large, hard-pressed cake resulting from batch pressing is avoided. The press (Figure 6) consists of a hopper with an oscillating wall feeding casein between two rollers, one of which is solid and chromium plated and the other is perforated bronze. The oscillating side of the feed hopper forces the curd between the two rolls, and their pressure against each other forces water through the perforated roll to the drain. The cake sticks to the perforated roll and is continuously scraped off by a wooden scraper knife into a hopper from which it is conveyed to the drier. (The press was built by Ireland Machine & Foundry Company.) These operations provide a relatively porous mass of flocculent casein which is low in acid and ash and in excellent shape TABLEI. AXALYSESOF CASEINFROM DIFFERENT SOURCES for drying in any convenient way. Practice has been to dry SOURCn ASH .4CIDa PH SOLUBILITY IN BORAX the casein on trays in a tunnel drier, but other more satis% Cc. % of bOTaZ factory and quicker methods have been developed. The disArgentina 2.02 8.2 4.26 16 Sulfuric 1.60 7.8 3.46 18 advantages of the tray drier are obvious. Casein, pressed to 3.35 7.2 4.70 12 remove moisture, is in more or less coherent pieces and tends 4.75 13.0 4.55 18 Lactic 2.77 19.6 3.80 22 to form a skin on the surface when heated which holds mois2.47 11. 4.22 16 ture within the piece. Since it is also difficult to remove acid 2.48 10.4 4.22 18 Hydrochloric: and ash uniformly from the casein produced by the older Batch procese 2.76 10.6 3.68 22.5 Grain-curd process 2.78 8.90 4.5 15 methods, hydrolysis takes place with the consequent damage New process 1.08 0.2 4.80 8 1.60 1.6 4.67 12 to the product as its temperature is raised. Improved driers (1) evaporate the residual moisture from Amount of 0.1 N sodium hydroxide required to neutralize 50 cc. of the filtrate secured from a mixture of 10 grama of casein and 100 cc. of distilled finely divided casein by picking up the particles in a stream water. of dehydrated heated air. Because these particles are relaThe whey, which contains valuable constituents, is sepa- tively small and quickly dried by the action of the air current, rated from the curd in an inclined trough provided with a hydrolysis and other similar effects are minimized. The screw conveyor shown in Figure 3 (built by the Jeffrey Manu- most successful driers are based on an adaptation of the facturing Company). The curd settles and is carried upward spray-drying principle. The casein from the continuous out of the whey by the conveyor flights. The clear whey, press, in a fairly fine state of subdivision, is picked up by a from which the curd has separated, is drawn off continuously rapidly moving stream of hot dry air and carried through a series of flues. These flues have sections of large diameter from near the surface a t the lower end of the trough. This whey from the precipitation contains lactose, in- placed a t intervals during their course where the velocity organic salts, and some residual albumin. It is utilized in of the air stream is so reduced that heavier particles are several ways. It may be evaporated direct to powder to yield dropped out and removed for further disintegration before a valuable feed for poultry and stock; it may be worked up for return to the system. The finer particles are carried on by the its lactose content; it may be fermented to yield lactic acid; air stream. The final dried dust ( 5 to 7 per cent moisture) or, as has been recently proposed, its albuminous constituents is removed from the moist air by a turboclone blower which may be separated and used. Since there is usually an excess supplies suction to the system. It is then ground to the of whey, the particular use to which it is put depends upon the requisite fineness to meet the market demands. The principal advantages inherent in the new method existing demand for products that can be made from it. During the settling process the warm curd has a strong tend- are : ency to cohere into large clots. After these are drained to 1. TJniform and immediate mixing of milk and acid. free them substantially from whey in the latter part of their 2. Uniform and prompt separation of curd from whey. 3. Use of hydrochloric acid which yields easily soluble salts upward progress, they are dropped into a disintegrator or ash constituents. beater. This disintegrator (Figure 4) consists of a per- with inorganic 4. Thorough and uniform washing of soluble impurities from forated metal cylinder in which revolves a shaft provided with the casein. arms that break the clots into small pieces under streams of 5. Continuous pressing which prevents the formation of large aggregates. cold water. 6. Prompt drying of small pieces of curd to prevent surface The disintegrated curd is washed through the perforated skinning that would hold moisture and acid in the particles and metal screen into an upward-inclined washing trough, and promote hydrolysis. pushed against gravity and a stream of cold wash water by a 7. A finished casein superior t o that made by other methods. second screw conveyor (Figure 5). This washer is similar to LITERATURE CITED the whey separator except that large quantities of water wash the whey from the curd. The curd is delivered a t the upper (1) Chamell, F. L..U. S. Patent 1,892,233 (Dec. 27,1932), and others pending. end of the washer practically free from water-soluble impuri- (2) . . Roaers. L. A., Associates of. “Fundamentals of Dairy Science,” ties. This slow, thorough, continuous washing yields casein A.C. S. Monograph, Chemical Catalog Co., N. Y.,1928. in relatively small pieces containing very little excess acid or (3) Sheffield, W. H.,U. S. Patent 1,716,799 (June 11, 1929), and others pending. ash. Edwin, “Casein and Its Industrial Applications,” The discharge from the washer delivers curd to a con- (4) Sutermeister, A. C. S. Monograph, Chemical Catalog Co., N. Y., 1927. tinuous automatic press of unique design which presses ( 5 ) Trimble, C. S., and Bell, R. W., Dept. Agr., Circ.279 (July, 1933). adherent water out of the mass and leaves it with about a (6) Van Slyke, L. L., and Price, W. V., “Cheese,” Orange Judd Pub. Co., N.Y.,1927. 50 per cent moisture content. Moisture is removed continuously in this Yecently developed pressing operation, and in RECEIVED March 23, 1934.
