Dairy Byproducts

by EARLE O. WHITTIER

WHENEVER more milk is produced than is needed to supply the demand there arises the problem of disposal of the surplus. One solution is to increase consumption by urging greater use of milk, a slow method, or reducing prices, not always a feasible method. The problem usually is partly solved by converting the surplus milk into relatively nonperishable products like butter, whole-milk cheese, evaporated and sweetened condensed whole milk, and dried whole milk products that can be easily stored or transported to places that need them.

The greatest money value of whole milk is in the milk fat, so primary emphasis is put on products containing all or most of the fat. Its value, though, makes it impractical to consider the use of milk fat for nonfood purposes; many cheaper fats are available and suitable for such uses. It is generally true that use in food is the most gainful way to utilize all the components of milk.

The production of butter and cheese from surplus milk leaves, as byproducts, skim milk, buttermilk, and whey, which also are byproducts in the making of cream, butter, ice cream, and cheese from nonsurplus milk. The problem of disposal of surplus milk includes, therefore, not only the primary one relating to the milk fat and foods containing milk fat, but also finding use for the practically fat-free byproducts.

The problems of disposition of surpluses and byproducts of the dairy industry are not new. They were becoming increasingly acute in the years before the war. During the war there were other problems insufficiency of food and feed but they are gradually disappearing again, and the utilization of surpluses and byproducts requires increased attention.

A general prejudice against the use of fluid skim milk as food has existed among our people, presumably mostly because so much of it has been fed to animals. In what degree skim milk is less palatable than whole milk is a question each individual must answer for himself. But the nutritive value of skim milk is not a matter of opinion. It is a matter of fact. Skim milk lacks the fat and the accompanying vitamin A of whole milk, but is equally rich in protein, lactose, calcium, phosphorus, and riboflavin. The diets of many individuals lack adequate calcium and riboflavin. Most of the skim milk used as food in the fluid condition is consumed as chocolate milk and cultured buttermilk. This indicates that added or developed flavor is an effective means of making skim milk attractive as a drink and has led to efforts to produce other flavored milks. The canned caramel-flavored milk, developed by the Bureau of Dairy Industry in conjunction with a manufacturer of evaporated milk, is one result of such efforts, but, since the recommended formulas include some fat, it is not strictly a skim-milk product.

The conversion of skim milk into cottage cheese is a convenient means of concentrating the protein for easier distribution and for marketing in a more popular form. Nutritively, cottage cheese lacks most of the riboflavin, lactose, and minerals of skim milk, but it is an excellent source of protein. Improvements in the texture, palatability, and uniformity of cottage cheese in recent years, resulting from work in the Department and several State experiment stations, have increased its popularity.

Skim milk in its concentrated forms is a convenient source of nonfat milk solids in ice cream. The proportion that can be used has been limited by the tendency of the lactose to crystallize in the ice cream. Because the crystallized lactose is hard and slow to dissolve, the ice cream sometimes had an objectionable sandy texture. To solve the problem, a low-lactose skim milk has been developed.

If skim milk is concentrated sufficiently to cause lactose to crystallize, it becomes so viscous that the crystallizing lactose is finely divided and difficult to separate, but if cane sugar is added to the skim milk before evaporation the concentrated skim milk is thin and the lactose crystals are large and can be separated easily by filtering in a centrifuge. Since cane sugar is needed as an ingredient of the ice cream, it can be supplied in the skim milk as suitably as at a later stage. The lactose removed from the skim milk is a valuable product. This procedure has been used profitably in dairy plants that make ice cream.

The use of fluid skim milk in bread and other bakery products is limited, largely because of its perishability and its bulk. Plain and sweetened condensed skim milk are popular sources of milk solids in bakery products, the latter being an especially convenient form when both milk solids and sugar are required. Dried skim milk is the form most generally preferred for incorporation in foods because of its high degree of concentration and its excellent keeping quality. It improves the texture, physical appearance, and flavor of many food products, and increases their nutritive value. The largest use of dried skim milk is in bread. Department chemists showed in 1927 that the heating of skim milk to 85 to 95 C. for a short period before drying had the effect of improving the baking quality of a bread dough mix in which the dried skim milk was used. As a result, practically all the skim milk dried for use in breadmaking in this country is given this heat treatment before drying.

When only the protein of skim milk is required, as in cheesecake, pot and bakers' cheese are used. In cities in regions of meager milk supply it has been the practice for some years to make cottage cheese from reconstituted dried skim milk. Recently technicians have demonstrated that a satisfactory bakers' cheese can be made from dried skim milk. This makes it possible for bakers in large cities at a distance from milk-producing areas to obtain freshly made bakers cheese.

One possibility of utilizing both skim milk and surplus potatoes is in making a wafer containing one-third skim-milk solids and two-thirds potato solids. Boiled potatoes and skim-milk solids are thoroughly mixed and seasoned and the mixture is extruded as a ribbon, which is then dried and toasted to a light brown. These wafers have a cheese-like flavor and the texture of potato chips. Having no fat, they will keep for a year or more. This special product has not yet been commercialized, but in the procedures involved are suggestions for many similar products.

The tendency of skim milk to foam when it is agitated is a troublesome factor in several dairy processes, but this property has been utilized to advantage in preparing home-made fruit whips. Sugar and fruit pulp are added to dried skim milk that has been reconstituted with one-half the usual quantity of water, and air is whipped in until the volume of the mixture is increased from one and one-half to four and one-half times the original. These whips are perishable and hence of no direct commercial interest, but this property of whipping can be put to use in many ways in home and restaurant kitchens.