FERMENTED MILKS 397 



be expected to accrue from their consumption. The food value 

 of fermented milks is nearly the same as that of sweet milk. The 

 difference between the food value of sweet milk and fermented 

 milk is a small reduction of lactose which is used by micro-organ- 

 isms in the formation of acids and gases, and as some fermented 

 milks are made of partially or wholly skimmed milk, the amount 

 of fat is diminished. Fermented milks have some advantages 

 over sweet milk, except that in some cases the acid is irritating to 

 the mucous membranes. One advantage is common to all fer- 

 mented milks, namely, the condition of the casein which is pre- 

 cipitated and, therefore, partially digested. Furthermore, the 

 presence of carbon dioxid gas in some fermented milks is stimu- 

 lating and favors digestion. The use of fermented milk as food 

 is, therefore, indicated in many cases of weak digestion. Metch- 

 nikoff advises a reduction of protein in the diet when fermented 

 milks are used, and it cannot be denied that the addition of an 

 easily digested food, such as fermented milk, to the diet may be 

 of considerable advantage if the amount of other food is reduced 

 proportionately. But beneficial effects can hardly be expected 

 when the milk is added to the usual diet without modification. 



Buttermilk has also been used for infant feeding, and there is 

 ground for the belief that it agrees in some cases when sweet 

 milk cannot be tolerated. The presumption that the acidity in 

 buttermilk is the cause of its digestibility has not been proved, 

 however, but the reduced amount of fat alone would render it 

 beneficial in some cases, and possibly skimmed milk would be as 

 readily digested as buttermilk. Furthermore, as stated before, 

 the casein is in more digestible form in buttermilk than in sweet 

 milk, and this may be an explanation of the success that has some- 

 times followed the substitution of buttermilk for sweet milk in 

 infant feeding. 



There are two classes of fermented milks, namely, those that 

 have undergone acid fermentation only, and those that have been 

 subjected to acid and alcoholic fermentations. In both classes 

 there are other properties that lend a pecuhar character to the 

 fermented milk. These differences depend upon the kinds of 

 micro-organisms that are active. Aroma is produced by yeasts; 

 in some fermented milks the protein is partly digested by micro- 

 bial activity; some fermented milks are viscous; and the amount 

 of alcohol and carbon dioxid developed varies in different milks 

 according to the kinds of yeasts present and the method of pre- 

 paring the product. 



