446 MICROBIOLOGY OF SPECIAL INDUSTRIES. 



The liquefaction of the starch is facilitated by slightly acidulating the 

 water with hydrochloric acid. The mixture is then cooled to 38 and 

 inoculated with a pure culture of the Mucor. A current of filtered air 

 is then passed through the mass for twenty-four hours, by which time 

 the mycelium has permeated the mass. The temperature is then reduced 

 to 33> P ure yeast added and aeration continued for twenty-four hours 

 longer to promote the multiplication of the yeast. Conversion of the 

 starch and fermentation of the sugar then continue together. The 

 mucor is capable of fermenting the sugar and producing alcohol, but 

 the yeast acts more rapidly. 



The malting process is the most commonly employed. The acid process destroys 

 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 general use. 



The starchy substances used being usually neutral or of low acidity the sugar solu- 

 tions 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 quan- 

 tity of free mineral acid remaining in the completed solution prevents 

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

 bacteria are restrained by lactic acid produced by lactic bacteria, originat- 

 ing 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 develop- 

 ment of acetic or other injurious bacteria. When the acidity of the 

 solution reaches 3.5 g. to 5 g. per liter the dangerous 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. By gradually increasing 

 the amount, moreover, yeast can be accustomed to amounts of antiseptics 

 which render the growth of bacteria impossible. An application of this 

 principle is found in the use of sulphurous acid in wine-making. 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. 



