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Dr. E. V. McCollum for the International Health Commission, and have been connected with laboratory investigations in which dried milks have constituted the chief part of experimental diets.

The evidence which has come to us from these different sources is quite consistent, and plainly places dried milk with pasteurized milk as regards the various factors of food value. In both cases the only significant change which occurs as the result of the heat treatment with its attendant manipulations, if properly conducted, is a diminution of the antiscorbutic vitamin. This has already been recognized as a possible result of pasteurization, and it is now a generally accepted practice to give orange juice or some other suitable antiscorbutic to all infants artificially fed on any other than fresh raw milk. The orange or tomato juice thus given primarily as an antiscorbutic is undoubtedly beneficial in other aspects of nutrition as well, and with this addition to the diet it becomes unnecessary to debate further as to the extent to which the antiscorbutic vitamin present in the milk is diminished in the drying process or whether there is greater destruction when the drying is accomplished by one mechanical process than by another. The original vitamin content of the milk, its freshness when dried, and the manner in which the drying process and the subsequent handling of the product is conducted are all factors of possibly equal importance with the mechanical principle on which the drying process is based. It is important also to remember that the processes for drying milk are still undergoing development and modification. In our opinion, it would be a mistake to prejudice the development of the industry at this early stage by any expression of preference as between the different drying processes, based merely upon consideration of the antiscorbutic vitamin. We think it much better to recommend that an antiscorbutic be given in all cases in which dependence is placed upon either pasteurized or dried milk by whatever process prepared. In fact, in view of the dependence of the antiscorbutic value of milk upon the diet of the cow (or of the mother), it may be advisable that all children receive an antiscorbutic.

Aside from the question of antiscorbutic vitamin, which easily can, and in our opinion always should, be provided from other sources, we believe that milk dried by any of the modern methods properly conducted is the equivalent of the fresh milk from which it was prepared.

The British report above referred to states explicitly "that cow's milk, during the process of desiccation, loses none of the characters which are necessary for the support of normal growth in infants." The United States Public Health Service also reports highly favorable results from the use of dry milk products in infant feeding. McCollum records most excellent results from the addition of dried milk as sole milk supply to the dietary of

an institutional group of children, and many experiments could be cited in which dried milk as a sole food has supported good health and normal growth in the rat for periods much longer than would correspond to infancy and early childhood in the human subject.

We believe there is ample evidence to support the position taken by the Commission on Milk Standards that there is no occasion for prejudice or discrimination against dried milk as compared with pasteurized milk even as concerns the most delicate factors of nutritive value.

Since the best standards of nutrition and health require not only the conservation of our present milk supply but its increase, in order that the per capita consumption of milk may grow with the knowledge of the food value of milk and its proper place in the diet, it is important that the drying of milk be considered also from the standpoint of the effect of this industry upon the dairy industry and milk supply as a whole.

The opinion is widely held and in our judgment well founded, that the dry milk industry will not seriously compete with or in any way injure the fluid milk industry as it now exists, but, rather, will supplement it and make possible the good use of its seasonal surplus; that with increasing recognition by consumers of the great importance of milk as food for adults as well as for children, dried milk will come to be largely used in cookery without diminishing the consumption of milk in fluid form; that the drying of milk both as a means of preservation and of greatly reducing transportation costs will permit the extension of the milk industry into regions too distant from large markets to ship milk in fluid form; that because of this extension of the source of supply, the greater consumption of milk in its different forms should not necessarily result in higher prices; that the drying of milk will greatly facilitate the production and handling of milk in the South where lack of natural ice so greatly hampers the fluid milk industry and where an increased use of milk in the diet is so urgently needed and will doubtless do more than anything else toward the lowering of the infant death rate and the suppression of pellagra among adults.

The manufacture of dry milk grew rapidly during the war. The production in the United States in 1920 was estimated at over ten million pounds. Most of this was skim-milk powder or flakes because legal restrictions hamper the sale of skim milk as such to the consumer, while, on the other hand, it is more easily dried than whole milk and yields a product which is more readily

kept, the fat of the whole-milk powder being liable to become rancid on storage unless kept under special precautions.

Cream and Skimmed Milk

Cream may be obtained from milk either by gravity or by centrifugal force. The prevailing method at present is by means of centrifugal separators in which the milk flows continuously into a rotating bowl containing thin metal plates which separate the milk into inclined sheets in which by centrifugal force the heavier "skim " milk is thrown toward the outer rim1 and the lighter fat globules are forced toward the center. Thus while the separator is in operation a continuous stream of cream and another of skimmed milk are obtained from the inner and outer layers respectively of the rotated bowl of milk. In order that the skimmed milk shall not be thrown out of the machine with too great force, the tubes which receive it from the outer portion of the bowl are carried back toward the center of the bowl, where they discharge into an outlet pipe. The size of the skim milk outlet may be made to bear any desired relation to the size of inlet, size of bowl, and speed of rotation, and thus any desired proportion of the whole milk may be drawn off as skimmed milk while the remainder is forced to the center of the bowl and discharged through the cream outlet.

If the skimmed milk outlet is set to discharge only one half of the milk entering the bowl, the other half must discharge through the cream pipe and a large volume of very thin cream having only twice the fat content of the original milk will be obtained.

If the skimmed milk tube be set to take nine tenths of the amount of milk which flows in, a small amount of rich cream having about ten times the fat content of the original milk will result.

To a considerable extent these proportions and the resulting

1 Suspended solids heavier than the skim milk are forced against the outer wall and result in a deposit of "separator slime."

amount and richness of the cream may be controlled by regulating the rate of inflow of milk without changing the size of the discharge pipes or the rate of running the machine. Thus, as illustrated by Wing: "If the milk is turned into the bowl at such a rate that 0.8 escapes through the skimmed milk outlet we shall have 0.8 skimmed milk and 0.2 cream. If now we reduce the rate of inflow by o.1, we shall get just as much skimmed milk as before, but only half as much cream; or if the inflow is increased by 0.1 we shall get the same amount of skimmed milk and one and one half times as much cream." In the first case, we should get from 100 pounds of milk with 4 per cent fat, 80 pounds of skimmed milk with, say, o.1 per cent of fat, and 20 pounds of cream with 19.6 per cent fat; in the second case from 90 pounds of the same milk, 10 pounds of cream with 35.2 per cent fat; in the third case from 110 pounds of the same milk, 30 pounds of cream with 14.4 per cent of fat. This assumes that the completeness of the separation will be the same, which should be true so long as the separator is run within the range of its capacity. McKay and Larsen state that in skimming milk for butter making, separators are usually run to yield cream with 25 per cent to 50 per cent fat, but that most separators will do good skimming even up to a cream of 60 per cent fat content. When the separator is well managed, the skim milk does not contain over o.1 per cent fat.

Since cream is an artificial product of such variable composition, it is obvious that any standard which may be set for the fat content of cream must necessarily be rather arbitrary. The standards which have been adopted appear to have been based largely on the fat content of the cream formerly obtained by the gravity process.

The standard recommended by the Association of Official Agricultural Chemists requires not less than 18 per cent of milk fat; and this has been adopted by a large proportion of the states. A few states have other standards.

The full definitions and standards adopted in 1919 by the United States Department of Agriculture as a guide for the officials of the department in enforcing the Food and Drugs Act are as follows:

1. Cream, sweet cream, is that portion of milk, rich in milk fat, which rises to the surface of milk on standing, or is separated from it by centrifugal force. It is fresh and clean. It contains not less than eighteen per cent (18.0%) of milk fat and not more than two tenths per cent (0.2%) of acid-reacting substances, calculated in terms of lactic acid.

2. Whipping cream is cream which contains not less than thirty per cent (30.0%) of milk fat.

3. Homogenized cream is cream that has been mechanically treated in such a manner as to alter its physical properties, with particular reference to the conditions and appearance of the fat globules.

4. Evaporated cream, clotted cream, is cream from which a considerable portion of water has been evaporated.

Market cream is apt to be at least half a day older than the corresponding grade of market milk and almost invariably has a higher bacteria content.

The Commission on Milk Standards recommends that cream be classified on the same plan as milk except for the number of bacteria permitted, which may be five times the number permitted in the corresponding grade of milk.

The Commission recommended that all cream be sold either on a guaranteed fat content or with a minimum standard of 18 per cent milk fat; also that cream should contain no constituent foreign to normal milk.

Nutritive value of cream. This will depend upon the composition and nutritive value of the milk from which the cream is taken and the extent to which the fat globules of the milk are concentrated in the cream, which latter factor, as explained above, is controllable within wide limits now that centrifugal separators

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