FERMENTED MILK 507 



active type of Bacterium caucasicum forms the inactive lactic 

 acid, while 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 occasionally. Some of these may have an influence 

 on the flavor, while others are inert. It is probable that there 

 are none, with the exception of Bad. caucasicum, that cannot 

 be replaced by other species without appreciably affecting the 

 results. Doubtless slightly different varieties of fermented 

 milk have developed in different localities owing to different 

 combinations of bacteria or of bacteria and yeasts. The Egyp- 

 tian 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 Bact. caucasicum, and it is prob- 

 able that if it is not essential it is of some assistance in starting 

 the lactic fermentation and, especially if the temperature is 

 low, in suppressing contamination before the Bact. caucasicum 

 has time to develop sufficient acid to check extraneous bacteria. 



Hastings and Hammer could not detect evidences of pro- 

 teolytic 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 cannot be considered as having any influ- 

 ence 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. 



"Yogurt buttermilk" is now sold in several cities, and the 

 growing demand will doubtless soon extend its manufacture 

 more generally. In making yogurt in this country better 



