FERMENTED MILKS 243 



may be used; but this yeast cannot ferment lactose, hence 

 cane sugar must be added to the milk. The yeast may be 

 added directly to the buttermilk, but better results are se- 

 cured as follows: To four ounces of boiled water, add about 

 ten grams of cane sugar and one third of a yeast cake. Do 

 not add the yeast till water is cooled. Keep in a warm 

 place (70 to 80 F.) over night, or for about ten hours. 

 This produces an active culture of the yeast. To each 

 quart bottle of buttermilk add 15 grams of cane sugar 

 and 2 c.c. of yeast culture. Cap the bottles with patent 

 stoppers or other tight caps that will withstand gas devel- 

 opment within the bottle. Keep at a temperature of about 

 60 F. for from three to four days with occasional shaking 

 to break up the curd. At the end of this time, the prod- 

 uct will be ready for use. Fermentation at a high tem- 

 perature, and continued for too long a time, produces a 

 strong undesirable flavor. The amount of alcohol and 

 carbon dioxide developed depends upon the amount of 

 sugar added to the buttermilk. The theoretical quantity 

 of alcohol formed is about one half the quantity of sugar 

 fermented. The carbon dioxide, rather than the alcohol, 

 is the desirable product of the yeast fermentation. The 

 quantity of sugar to be added is governed by the quantity 

 of carbon dioxide desired. Fifteen grams of sugar in one 

 quart of buttermilk (i per cent of sugar) produces the 

 desirable effervescence, and the sharp taste of charged 

 water, but will not cause an excess of gas. 



A similar product may be made from skim milk instead 

 of buttermilk. In this case the milk should be pasteurized 

 and a slightly larger percentage of sugar (two to three per 

 cent) be used. This product lacks the sharp acid flavor 

 of the buttermilk product, but has the pleasant gas- 

 charged flavor. 



