INDUSTRIAL AND ENGINEERING CHEMISTRY
54
Discussion
One of the objections to the recovery of lactose by the desiccation processes here outlined is the fact that substances in the sirup other than the sugar appear in the dried product. For most purposes, such as for use in modified milk and for correcting the intestinal flora, these so-called impurities would not be detrimental. Because spray-dried amorphous lactose is hygroscopic and has poor wetting properties it is of doubtful commercial value. Also its saturated and highly concentrated solutions soon begin to deposit crystalline alpha because they are supersaturated with respect to it. Theoretically it should be possible to obtain highly concentrated solutions of this and other products which are mixtures of alpha and beta lactose, since the solubilities of individual substances are additive. The drum-dried products were largely amorphous, but more nearly crystalline in appearance than the spray-dried products. They were nonhygroscopic under ordinary room temperature and humidity conditions and had good wetting properties. The cost of the drying operation is variable, depending among other things, on the size of the unit used, the revolutions per minute of the drum, and the concentration of the solution. It has been estimated that the cost of dry-
Vol. 22, No. 1
ing enough 27.7 per cent lactose solution to make a pound of beta lactose is $0.008 when a 32 by 90 inch atmospheric double drum drier is employed. The cost of manufacturing the sweeter and more quickly soluble beta-anhydride lactose under the conditions just described should not exceed that of the alpha-hydrate lactose of commerce. Acknowledgment
The writer is indebted to the Douthitt Engineering Company, Chicago, Ill., and to the Buffalo Foundry and Machine Company, Buffalo, N. Y., for assistance in conducting some of the experiments discussed in this paper. Literature Cited Erdmann, Ber., 19, 2180 (1880). Gillis, Rec. fruu. chim., 99, 88 (1920). Hudson, Princeton University, Bull. 19 (4), 63 (1902). Hudson, Z. fihysik. Chem., 44, 488 (1903). Hudson, J . Am. Chem. Soc., 30, 1767 (1908). (6) Hudson and Brown, I b i d . , SO, 960 (1908). (7) Pictet and Vogel, Comfit. rend., 185, 332 (1927). (8) Pirtle, Private communication. (9) Schmoeger, Ber., 13, 1915, 2130 (1880); 14, 2121 (1881). (10) Sharp, Unpublished data. (11) Tanret, Bull. SOL. chim., 3, 15, 349 (1896). (12) Verschuur, Rec. Lruv. chim., 47, 123 (1928). (13) Wright, J . Dairy Sci., 11, 240 (1928).
(1) (2) (3) (4) (5)
Manufacture of Casein and Lactose from Skim Milk' Fred P. Nabenhauer SMITH, KLINE8. FRENCH LABORATORIES, PHILADELPHIA, PA.
ROM a practical standpoint skim milk is considered to be composed of casein 3 per cent, albumin 0.7 per cent, lactose 4.5 to 5.0 per cent, and mineral constituents about 1 per cent. The casein content varies from 2.7 per cent in the spring, or when the flow of milk is greatest, to 3.3 per cent in the winter. The other constituents do not vary so widely and depend on such factors as the breed of cows supplying the milk and the care and rapidity with which the milk is handled. These are especially important to the sugar yield. The casein is precipitated from the milk by the addition of either rennet or acids. Although this paper deals principally with muriatic casein and its whey, it will be necessary for comparison to describe briefly the steps in the various methods and t o point out the differences in the products obtained. These methods are all described in greater detail by Sutermeister ( 2 ) .
F
Preparation of Rennet Casein
I n the preparation of rennet casein the milk is warmed to 96" F. and treated very much as in the manufacture of cheese, with sufficient rennet to bring about curdling within 15 to 20 minutes, during which time it is stirred and gradually warmed t o produce a curd of suitable size for washing. After settling it is drained of the whey, washed with warm water to remove all the soluble impurities, and then pressed and dried. As it is used almost exclusively in the manufacture of plastics, rennet casein must be very carefully prepared and must possess the following properties: (I) high ash content and low fat; (2) freedom from mechanical dirt; and (3) nearly white color, free from colored particles. These qualifications can only be attained by (1) starting with very fresh and well-skimmed milk (any acidity increases 1 Received
October 19, 1929.
the solubility of the calcium phosphate in the milk); (2) cleanliness throughout all steps; (3) thorough washing and pressing; and (4)drying as rapidly and a t as low a temperature as possible. Preparation of Self-soured Casein
The acid casein used most extensively for technical purposes is lactic or natural soured casein. The milk, warmed to about 100" F. is allowed to undergo spontaneous souring or is aided by addition of sour whey from a previous batch. After a few hours the casein separates as a soft curd, which is brought together by direct heating with steam jets. The operator can judge when souring has reached the proper point and just how hot to cook the curd. If insufficient acidity has developed, the separation is incomplete and the curd is soft and stringy when heated. If too acid, it does not hold together and is liable to break up further on heating. The curd is pushed back from the gate with a screen and the clear whey drained off as thoroughly as possible, some of it being saved for the next run. A stream of cold water is run through the curd to remove excess whey, but this washing seems rather superficial and does not greatly reduce the ash content of the casein. After draining it is shoveled into hydraulic presses and gradually freed of as much moisture as possible. This type of curd is usually soft and soggy and cannot be pressed very dry. Often it is allowed to drain after pressing. It is then put through a shredding machine, which breaks it into small grains and spreads it on trays, which are placed in tunnel driers. After drying it is ground and sacked very much as muriatic casein described later. There are many other methods of heating and of using soured whey, the handling a t various steps being slightly different but the product being about the same in each case.
INDUSTRIAL AND ENGINEERING CHEMISTRY
January, 1930
Production of Muriatic Casein
The use of mineral acids is rather recent, and unfortunately the first artificially soured caseins were so inferior that muriatic casein came into great disfavor, and has only recently started to recover from the prejudice which it undoubtedly deserved. If the whey is to be used in the manufacture of lactose, the curd must be separated rather rapidly. This was a t first accomplished by warming the milk to 105-120" F. and adding sufficient dilute sulfuric or hydrochloric acid to bring about complete coagulation of the curd in large, tough lumps. Most of the whey could be drained off rapidly and the curd pushed out of the vat into a smaller vat. Here it was cooked by heating with steam until the whole mass formed one tough, doughy lump, which was kneaded to express excess whey, allowed to cool, and cut up into suitable sized chunks to go into the curd grinder, which in this case had to be extremely sturdy. The greatest advantage of this method was that the whey was free from casein and was received with very little delay a t the sugar side of the plant. This tough curd, when dried and ground, was very hard and flinty and did not wet rapidly; its ash content was very much higher than self-soured casein; and when dissolved in borax gave on cooling, instead of a fluid glue, a tough, leathery gel, in which condition it was said to have "livered." I n order to remedy this the paper coaters were forced to try other solvents; caustic soda seemed to be effective in reducing the viscosity, but it also ruined expensive brushes. These undesirable properties have been attributed to the use of hydrochloric acid, but this is not entirely justified. It seems necessary, however, to obtain a lower ash content in a muriatic than in a lactic casein to give a low viscosity. When cold milk is acidified, a very fine curd is obtained, but with very high temperatures it separates in large plastic lumps. If the milk is warmed to 95" F. and very dilute hydrochloric acid is added with good, but not violent, agitation, a curd is obtained in small grains which do not adhere and can be drained off and washed very easily. This is the basis of the grain-curd method. Agitation is another important factor in effecting uniform and intimate mixing of the milk with the acid. Too violent agitation is undesirable, since it breaks up the curd too much, especially if excess acid has been used. The acid must be fairly dilute and should be added slowly. Sufficient agitation reduces the danger of using too much acid. Only enough acid should a t first be used to give a clear separation. This occurs a t a pH 4.6-4.8. An excess of acid redissolves the curd, softening it so that handling becomes difficult. The effect of acidity of coagulation on the viscosity and ash content of the resulting casein is well illustrated in the following experiment: The casein was precipitated a t 40" C. from 900 cc. of skim milk by the addition of approximately 17 per cent hydrochloric acid. The curd was pressed as dry as possible in a cheesecloth sack and was dried. The ash was determined and the time of flow of a solution measured in an Engler viscometer on a solution made by dissolving at 65" C. 17 grams of the casein in 100 cc. of water containing 4 grams of borax. The viscosity is given as the time required for the flow of 10 cc. a t 25" C., all the solution being poured into the cup. ACID cc. 1.8 2.7
3.6 4.5 5.4 6.3
ASH Per cent 3.86 3.50 2.79
2.48 2.36 1.97
VIscosrrY Seconds 1020 900 185 130 80 90
It would appear from this that to obtain a low ash and viscosity it is only necessary to add more acid. Practically,
55
however, this is not done since very acid curd is difficult to handle and yields a too acid casein. The ash content may be reduced more conveniently by washing the curd with water or very dilute acid, as in the grain-curd method. To a certain extent the nature of the acid affects the firmness of the curd, sulfuric giving the best curd to handle and lactic the softest. Consequently, if some souring has taken place, the curd will be softer than if sweet. Pasteurization also affects the workability of the curd. The higher the temperature and longer the heating the higher will be the temperature necessary to give a satisfactory curd. The grain-curd method gives casein that has low ash content and good solubility in alkalies. It can be used only when the milk supply is uniform and of low acidity. The milk is treated as described above to obtain a granular curd. Most of the clear whey is allowed to drain and sufficient acid is added to the residue to bring the acidity to 4.6. Washing with acidified water and decantation reduces the ash content to any desired point. What is known as "pressed curd" is perhaps the best adapted t o a mixed milk supply. The milk is precipitated a t a slightly higher temperature, producing a rather coarse curd. The whey can be separated almost immediately and is pumped to the treating tanks. The curd is not cooked, but is pressed either with or without washing (which is not very effective with such large masses). Several kinds of presses have been used, such as hand presses used for cheeses, hydraulic presses, and continuous fruit presses. In any method the treatment of the milk and the nature of the curd must be modified a t times to give the best results in the press which is used. The use of drain racks and screens aids in the removal of excess moisture before pressing. I n all methods the curd must be shredded before drying. The shredder tears up the curd into small shreds or grains and spreads them on trays, which are put into tunnel driers a t about 125' F. and allowed to remain until thoroughly dry. Long or over-heating may produce brown particles due to the caramelization of sugar, especially when the curd is very wet. Darkening also occurs more readily in drying casein with high ash content and low acidity. When dry, the casein is ground to a suitable mesh and sacked. Uses of Casein
We might classify caseins according to the ash content as follows : CLASS Very high
High
Medium
Low
EXAMPLE Rennet Cooked curd Pressed curd, self-soured Grain curd
ASH CONTENT Per .crnf . 8 4-5 3-4 2 (or under)
Rennet casein is used in making plastics. It is never put into solution, but must form a plastic mass when heated with water. Here a high ash content is necessary for proper working and molding. Cooked curd and other acid caseins are used chiefly in paper coating, glues, cold-water paints, and in other places where its gluelike nature is desirable. In these uses it is necessary to dissolve it. Particularly in paper coating is it necessary to have a smooth flowing solution when dissolved in such solvents as borax, ammonia, and sodium phosphate, carbonate, or hydroxide. The glue thus formed acts as an adhesive for the clay and other pigments used for coating. Paper coaters have found that lactic casein gives uniformly good results. It is therefore expedient, when manufacturing muriatic casein, to maintain a product that can be used interchangeably with self-soured casein in the various coating mixtures. A good pressed curd will do this but, as previously mentioned,
56
INDUSTRIAL AATDENGINEERING CHEMISTRY
cooked curds “liver.” Grain curd has excellent solubility, but on account of the slightly lower yield due to more thorough washing it commands a higher price, The value of casein in most other fields depends on the irreversible gel formed by the solutions in lime. Lime-casein glues thicken and set rapidly and are therefore quite waterresistant. Mixed with insecticides casein produces better spreading and more permanent films, which are not easily washed off by rain. Production of Lactose The whey from hydrochloric or rennet casein can be utilized in making lactose. The presence of sulfates would lead to the production of turbid sugar, and although lactose can be made from whey in which some lactic fermentation has taken place, the yields are greatly decreased. The presence of phosphate ion in acid whey makes it necessary to employ a different procedure than that used in working u p rennet whey. The whey is heated in large iron tanks with direct steam. Milk of lime is gradually added until the acidity is 6.2, using bromothymol blue. A trained operator learns to judge this very closely by the appearance of the coagulum which forms. Too much lime causes caramelization during heating and evaporation. Overliming may take place if improperly slaked lime is used. If too little lime is used, the whey later foams badly in the first stages of evaporation. The heating is continued very nearly to boiling. The coagulated albumin rolls about in fairly large masses, which rise to the surface in a compact layer when boiling is stopped, allowing the clear whey to be drained from below and run into a reservoir from which it is drawn into the vacuum pan. The albumin layer is dropped into mud boxes and later pressed. The neutralized whey is evaporated to a sirup (about 20” Be.) in double-effect pans. At times there is excessive foaming in the first pan. This may be remedied somewhat by treating a t a slightly higher pH or by adding oils. Careful cleaning of the pans also helps in reducing foaming. Various theories are circulated among sugar makers for this condition known as “wild whey.” As it occurs in the spring it is usually attributed to green feed, but it is also likely that a t this time there is more non-coagulated protein present in the milk. The thin sirup is filtered in a filter press, which is then used to filter the albuminous “mud.” The filtrate removes the excess of sirup from the press and is added to the whey. When a day’s run of sirup has been collected, it is evaporated further in a single-effect pan to about 40-45” B6., when it starts graining in the pan. As in cane-sugar crystallization, it requires skill on the part of the pan man to obtain a good grain. Foaming and boiling over a t this point are prevented by adding strong hydrochloric acid. Although this seems like bad practice, it is important a t this point to have rapid evaporation. The acid prevents scale to some extent and gives a lighter colored sirup. It also appears to have some effect on the growth of the crystals. Formerly the hot sirup was dropped into wooden boxes and allowed to crystallize over a period of several days. The labor later required to handle it has led to the use of agitators, jacketed to allow rapid cooling. When crystallization is considered complete, the yellow mush of crystals is dropped into a centrifuge, freed of mother liquor, and washed with cold water. The sugar obtained is yellowish although quite pure. If the grain is small or much albumin has precipitated, the washing is made difficult and losses occur. Such bad sugar is caused by lactic fermentation, poor treatment of whey, leaky or dirty pans causing high evaporation temperature and prolonged heating, broken filter cloths, too rapid agitation or cooling, and perhaps other factors.
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The mother liquors and wash waters may be concentrated and allowed to crystallize in wooden boxes. The sugar so obtained is coarse, but is difficult to separate from the very viscous sirup without the use of much water. The mother liquors from this crop are very high in salts and are discarded. When rennet whey is used, it is evaporated to a sirup before it is limed and filtered. Otherwise the processes of evaporation and crystallization are much the same. The process used for obtaining crude sugar from cheese whey has been described by Whittier (3). For refining, the crude sugar is dissolved in water to a thin sirup in large iron tanks. Bone black and hydrochloric acid or some vegetable carbon and phosphoric acid are added for decolorizing. The sirup is then warmed and treated with lime till a clear break of the carbon is obtained. This is a t some particular p H for each carbon used, but is about 5.45.8 using methyl red. To an experienced sugar melter the break is as reliable a guide as colorimetric tests. When properly treated the carbon flocculates and settles to the bottom of the tank, leaving a clear supernatant fluid which filters readily to a sparkling sirup. Too acid a treatment causes a cloudy sirup, and, if too alkaline, filtration is hindered by the presence of flocculent calcium phosphate. The sirup is pumped through a paper filter to a reservoir, from which it is drawn into a vertical, jacketed copper pan and evaporated to a density of 40’ BB., run into an agitator in which it cools and crystallizes. From this it is run into a basket centrifuge and washed thoroughly with cold water. The mother liquors and wash waters are used several times to dissolve crude sugar, When too salty they are returned to the crude sirup tanks. The refined sugar is spread on trays and dried in a tunnel drier or, better, in a drum drier. It is pulverized to 100 (regular) or 200 (impalpable) mesh and put up in 200-pound barrels. The yield of refined sugar averages about 2.5 per cent, or one-half the amount in the whey. This low yield may be due to lactic acid fermentation, hydrolysis, incomplete crystallization (due to salts and other impurities), poor evaporation, difficulties in washing, or mechanical losses involving loss of sirups from leaky pipes or other equipment. It is usually considered that 10 per cent is lost on refining. The press cake of albumin is broken up, dried, and sold for use in poultry feeds. It is about one-third ash (chiefly calcium phosphate), which accounts for the high yield of about 1.25 per cent. Considerable work has been done a t the Bureau of Dairying by Bell, Peter, and Johnson on the preparation of soluble albumin (1). The difficulty of removing salts and sugar from the product to make it more nearly resemble egg albumin has prevented it from becoming a commercial venture. The utilization of the molasses is another problem the only solution of which seems to lie in stock feeds. Literature Cited (1) Bell, Peter, and Johnson, J . D a i r y Sci , 2, 163 (1928). (2) Sutermeister, “Casein and I t s Industrial Applications,” Chemical Catalog, 1927. (3) Whittier, Chem. Rez.., 2, 85 (1925).
German Dye Outlook-The German Dye Trust development of the I. G.’s business continued satisfactory during the second and third quarter of 1929. Business in coal-tar dyes and intermediates showed a favorable tendency, and exports were lively. Business in chemicals, solvents, and pharmaceuticals was satisfactory, with increased exports, The I. G. is estimated to produce 75,000 metric tons of dyestuffs annually, valued a t 350,000,000 marks.
