MICROBIOLOGY OF ALCOHOL AND ALCOHOLIC PRODUCTS. 447 



per hectoliter and to the sugar solution in somewhat smaller amounts. 

 This results in the inhibition of lactic, butyric and other bacteria and 

 an increase in the fermentative power of the trained yeast. 



FERMENTATION. The sugar solution properly diluted and acetified 

 or sterilized is fermented by the addition of a mother yeast, usually taken 

 from a previous fermentation. 



The original yeast may be obtained by a spontaneous fermentation 

 as is usual in the manufacture of rum. Such a yeast is always impure, 

 containing various yeasts, molds and bacteria, and is therefore very 

 variable and uncertain in its results. 



In the fermentation of beet juice and beet molasses, beer yeast of the 

 Frohberg type or special distillers yeasts are used. A starter or mother 

 yeast is prepared for each vat or the process is made continuous by 

 leaving one-third to one-half of the contents of a fermented vat to start 

 a fresh addition of the sugar solution. With the latter method the yeast 

 in time becomes weak and badly contaminated and a new start must 

 be made with fresh yeast. 



In the fermentation of solutions made from potatoes, corn or other 

 starchy substances, each vat is started with a mother yeast. The tem- 

 perature should be kept below 30 by means of refrigeration, otherwise 

 alcohol will be lost by the multiplication of bacteria. 



By the use of pure yeast, the yield in alcohol is greater as no sugar is 

 wasted in the production of lactic acid. The cost, however, is greater 

 owing to the necessity of the use of more heat in sterilization. 



The fermentation of sugar-cane molasses for the production of arrack 

 is brought about by the use of a mother yeast called tape], prepared from 

 ragi or Java yeast. 



Tapej is made by mixing powdered ragi with boiled rice. In two 

 days the rice is reduced to a semi-fluid condition and contains bacteria, 

 molds and yeasts. The bacteria seem to have no part in the process but 

 when too numerous are injurious. The mold Mucor oryza converts the 

 rice starch into sugar and the yeast S. vordemanni produces alcohol from 

 the sugar. The other molds present are more or less injurious. 



