This is sometimes employed as a modification of milk by which the insoluble proteins are removed. Whey is prepared by adding a drachm of liquid rennet to half a pint of warm milk (104° F.). After the mixture has been stirred it is allowed to stand until coagulation has taken place. The curd is then broken up thoroughly and the whey is strained off through muslin or a strainer. Half a pint of milk yields 7 oz. of whey. The approximate composition of whey is as follows: proteins .8 per cent, fat 1 per cent, and sugar 4.75 per cent.
The chief protein is lactalbumin, the casein having been separated in the curd. Sometimes whole milk and sometimes separated milk is used, the difference in the result consisting of the larger amount of fat from the former. When whey is kept anytime or is to be mixed with other food it is necessary to heat it to a temperature of 160° F. or boil it in order to check further changes from the rennet ferment. When used as a food for infants the deficiency in fat must be made up by the addition of cream.
The advantages claimed for whey are that the proteins are very digestible, and although in small quantity they are sufficient, with the addition of those in cream. For ordinary cases it is doubtful whether the trouble of preparation is justified by the result, and whether the normal stomach should not be employed more actively in doing its proper work. As a temporary measure in cases of difficult digestion or disease whey is most useful, and its application in such cases will be considered later on.
Dr. Still considers that whey may be used with great benefit as a diluent of cows' milk in infant feeding. The proportion of curd-forming caseinogen is reduced without reducing the proportion of lactalbumin, and the mixture approximates more nearly to human milk in respect of its lactalbumin than is possible with any other diluent. He shows this in the following table.
Casein, 0.81 per cent.
Lactalbumin, 0.75 ,,
Cream (48 per cent fat)
Fat . . . 3.87 „
1/2 level teaspoonful.
Sugar . . 6.50 „
This is a very close imitation of breast milk as regards the chemical composition, but it requires very careful supervision of the ingredients and their preparation to ensure correct results.