634 MICROBIOLOGY OF ALCOHOLIC FERMENTATION 



together. The mucor is capable of fermenting the sugar and producing 

 alcohol, but the yeast acts more rapidly. 



The malting process fe the most commonly employed. The acid process de- 

 stroys a greater part of the value of the residues of distillation and the amylo process, 

 requiring costly special equipment and large expenditures for fuel, has not come 

 into genejral use. 



The starchy substances used being usually neutral or of low acidity 

 the sugar solutions produced would be very liable to bacterial invasion 

 unless means of prevention were used. 



In the amylo process, the sterilization of the solutions and the use of 

 pure cultures accomplish this end. In the acid process, the minute 

 quantity of free mineral acid remaining in the completed solution pre- 

 vents any considerable growth of bacteria. In the malting process the 

 injurious bacteria are restrained by lactic acid produced by lactic 

 bacteria, originating in the malt or in the yeast starter. The requisite, 

 bacteria are obtained by keeping the starter or mother yeast at 50 

 to 58 for a certain time. This is a favorable temperature for lactic 

 and too high for the development of acetic or other injurious bacteria. 

 When the acidity of the solution reaches 3.5 g. to 5 g. per liter the danger- 

 ous butyric bacteria cannot develop. 



Pure lactic acid may be added immediately after saccharification and 

 the loss of sugar due to the action of the lactic bacteria avoided, but 

 the high cost of the pure acid prevents the practice. 



Yeast being much less sensitive to the presence of certain antiseptics 

 than bacteria it is possible to control the latter by the addition of 

 suitable amounts of an antiseptic to the sugar solution. In certain cases 

 moreover by gradually increasing the amount, yeast can be accustomed 

 to concentrations of antiseptics which render the growth of bacteria 

 impossible. In Effront's method for the preparation of distillation 

 material, hydrofluoric acid is used. This acid is added to the mother 

 yeast at the rate of 10 g. 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. 



