FERMENTED MILKS 21 
frequently somewhat slimy, which ordinarily does not separate from 
the whey even on long standing. In 24 hours the milk may show 
acidity equivalent to nearly 2 per cent of lactic acid, and on standing 
several clays this may become about 3 per cent. The most active of 
the ordinary lactic-acid bacteria seldom exceed 1 per cent lactic acid. 
The more active type of Bacterium caumsicum forms the inactive 
lactic acid, whereas the levorotatory acid is produced by the type 
forming acid more .slowly. Small amounts of other organic acids and 
traces of alcohol are formed. 
This bacterium is evidently the essential organism of yogurt, 
matzoon, ceiddu, leben, and similar fermented milks. Other bacteria 
are always present, some of them habitually and others only occa- 
sionally. Some of these may have an influence on the flavor, whereas 
others are inert. It is probable that there is none, with the excep- 
tion of Bacterium caucasicum, that can not be replaced by other 
species without appreciably affecting the results. Doubtless slightly 
different varieties of fermented milk have developed in various locali- 
ties owing to different combinations of bacteria or of bacteria and 
yeasts. The Egyptian leben is reported to contain alcohol, but not in 
quantities sufficient to produce an effervescence such as is observed in 
kefir or kumiss. One of the ordinary lactic-acid bacteria seems to 
be always present with the B. caucasicum, and it is probable that if 
it is not essential it is of some assistance in starting the lactic fermen- 
tation and, especially if the temperature is low, in suppressing con- 
tamination before the B. caucasicivm has time to develop sufficient 
acid to check extraneous bacteria. 
Hastings and Hammer {36) could not detect evidences of proteo- 
lytic enzymes by the usual tests, but found in old-milk cultures a 
distinct peptonization of the casein which was not traceable to the 
action of the acid. This change is so slow and so small that it can 
not be considered as having any influence on the digestibility of the 
milk. Otherwise the only changes in the milk constituents are in the 
conversion of the sugar to lactic acid and very small amounts of 
volatile acids and traces of alcohol. 
In making yogurt in this country better results are obtained by 
using with the B. caucasicwn a culture of an ordinary lactic-acid 
organism such as is used in making buttermilk. B. caucasicum grow- 
ing alone in milk forms usually a rather slimy, tenacious curd which 
can not be broken up into the smooth, creamy condition essential to 
a good buttermilk. If this organism is grown in combination with 
the ordinary lactic-acid organism, a more friable curd is obtained, 
and the sliminess is not so evident. The two organisms can be 
carried in mixed culture only with great difficulty, as the high acid 
soon suppresses the ordinary form. The most satisfactory results 
can be obtained by making buttermilk in the ordinary way and 
churning it with an equal quantity of milk curdled with the j^ogurt 
organism. This procedure gives the desirable texture of buttermilk 
and a distinctive flavor. 
If a culture can be obtained, yogurt can be made in the home. 
With a reasonably active dry or fluid culture the following procedure 
should be satisfactory : 
One-half pint of milk is heated in a double boiler and held at the 
boiling point for one-half hour. This milk is cooled to about 100° F. 
