RELATION OF MICROORGANISMS TO SOME SPECIAL DAIRY PRODUCTS. 371 



each contains a variety of microorganisms, made up of at least one species 

 of yeast with one or more species of bacteria, capable of producing greater 

 or less amounts of acid. In some, as in the case of kefir, the yeast fer- 

 mentation is allowed to predominate, while in others, like yahourth, the 

 action of the yeasts is held in check by the rapid development of the acid 

 by the Bad. bulgaricum. All of these drinks are commonly recommended 

 by physicians because of their beneficial effect upon the digestive tract. 



ARTIFICIAL BUTTERMILK. Quite recently there has developed an 

 important industry in the manufacture of artificial buttermilk. This 

 is usually made by inoculating skim milk with a culture of lactic bacteria, 

 either our native Bad. lactis acidi, or one of the imported species, such 

 as Bad. bulgaricum. In making the artificial buttermilk, yeasts are not 

 commonly added. After the milk becomes coagulated, it is then churned 

 in order to give it a smooth, creamy consistency, after which it may be 

 bottled and kept for some time by holding at low temperatures. Some- 

 times a small percentage of whole milk is added at the time of churning 

 to make the finished product more closely resemble natural buttermilk. 

 In making artificial buttermilk, the skim milk is frequently pasteurized 

 in order to get rid of the miscellaneous flora which it contains. The 

 finished product, therefore, differs from ordinary buttermilk in the fact 

 that it contains nearly pure cultures of the lactic organisms while the 

 natural buttermilk will contain a more or less miscellaneous flora in 

 which the acid organisms predominate. It is possible to obtain a more 

 uniform product in the artificial buttermilk than in the natural product, 

 and this is perhaps responsible for the rapid development of this industry. 



FROZEN MILK. 



Some effort has been made to put upon the market milk which has 

 been frozen into cakes or bricks. This has been tried both in Europe 

 and in this country. Some difficulty has been met in satisfactorily freez- 

 ing the milk and holding it in a frozen condition. The process has proved 

 to be rather expensive and not very satisfactory. One difficulty with 

 this process seems to be that the quality of the frozen milk after it has 

 been melted is not as good as it was before it was frozen. From a bac- 

 teriological standpoint, this process is of some interest, but it is doubtful 

 whether it becomes of much importance commercially. 



