FERMENTED MILKS 7 
certain organs. This point could be determined only by a physician. 
It would be very unsafe to consume large quantities of milk, fer- 
mented or unfermented, under certain pathological conditions. In 
any case an important change in the diet should be made only upon 
the advice of a physician. 
VARIOUS KINDS OF FERMENTED MILK 
BUTTERMILK 
Buttermilk, properly speaking, is the milk remaining after the fat 
which collects in granules during churning is removed. If cream is 
churned when sweet the buttermilk does not differ from ordinary 
skim milk, but if it is churned when sour (the usual practice) the 
acidity is sufficient to coagulate the casein in the cream. In the 
churning process this curd is broken up into very fine particles. 
These curd particles settle very slowly, and if the buttermilk is 
agitated occasionally it will retain its milky appearance. When the 
buttermilk is allowed to stand undisturbed for several hours the curd 
particles sink to the bottom, leaving an opalescent whey at the top. 
At the present time a large part of the so-called buttermilk sold in 
cities is not buttermilk, properly speaking, since it is not made by 
churning cream, but is simply sour skim milk which has been 
churned or stirred in order to break up the curd. 
The souring of milk or cream is brought about by the activity of 
certain bacteria which form lactic acid by decomposing the milk 
sugar (lactose). The ability to form acid from lactose and other 
sugars is possessed by many kinds of bacteria but is so characteristic 
of a certain group that they are commonly spoken of as the lactic- 
acid bacteria, These bacteria have been described as distinct species 
or varieties under many names. Among them may be mentioned 
Bacterium guntheri-, Bacillus acid/i lactici, and Streptococcals lactis. 
In spite of the confusion in nomenclature it is evident that the term 
" lactic-acid bacteria " includes a fairly well-defined group of closely 
related varieties possessing in common several definite characters. 
Variations from the type in minor characters produce an almost in- 
finite number of varieties. These variations may be in the ability to 
ferment different sugars, in the tendency to grow in chains, in the 
kind of flavor formed in milk, in the intensity of acid formation, and 
in the ability to produce pathological conditions in animals. 
In many creameries the cream is allowed to sour spontaneously. 
In this case many bacteria other than the true lactic-acid bacteria 
will take part in the acid formation, and in addition to lactic acid 
the buttermilk may contain small quantities of acetic, succinic, and 
formic acids and sometimes traces of alcohol. The lactic-acid bac- 
teria form lactic acid, with only slight traces of other organic acids, 
no alcohol, and no gas. In well-managed creameries the acid fer- 
mentation is assisted and controlled to some extent by the use of a 
starter. This may be milk allowed to sour spontaneously or butter- 
milk from the previous day's churning, but careful butter makers 
build up starters from commercial cultures sold in the form of pow- 
ders, tablets, or fluid cultures, as varieties of lactic-acid bacteria 
selected with special reference to the production of a desirable flavor 
in butter. The butter maker puts this culture into about a quart of 
