570 CHAPTER XXVIIl 



Process used in Grain Distilleries^^. — It is of interest to compare the 

 above methods with those in use in cereal distilleries. The basis of manu- 

 facture is grain ; this is ground to a coarse powder and a weighed amount 

 is placed in a digester, mixed with water, and heated by steam under a pressure 

 of two or three atmospheres for an hour or more. The liquid contents 

 of the digester are then blown into a second vessel and cooled. As soon as 

 the temperature falls below 63° C, a proportion of malt is added ; the malt 

 contains a ferment, diastase, which converts the starch in the grain to a 

 sugar, maltose. After the starch has been so converted into maltose, the 

 contents of the vat are drawn off into a fermenting vat and rapidly cooled. 

 These vats are usually large enough to hold a whole day's work, and a dis- 

 tillery will have generally six fermenting vats, each of which may be of as 

 great a capacity as 50,000 gallons. After the vat is set up it is " pitched " 

 with yeast, and the temperature and quantity of yeast regulated with the 

 object of obtaining the maximum yield of alcohol within the legal limit of 

 time, i.e., 72 hours. The temperature is regulated by means of water circula- 

 tion through coils and maintained at 20°-25° C. ; the high temperature 

 promotes a rapid fermentation, but more fusel oils are formed than at a 

 low one. 



The preparation of the pitching yeast is as under : — A mixture of green 

 malt and water is warmed to about 70° C, kept at this temperature for about 

 two hours to allow the starch to be converted to maltose and soured. Green 

 malt contains enormous numbers of bacteria, amongst which are the lactic and 

 butyric acid organisms. Butyric acid is a virulent yeast poison, and its devel- 

 opment would injure the yeast. Yet these organisms cannot be killed by 

 raising the temperature, as this would also destroy the action of the diastase. 

 The butyric acid bacteria are, however, themselves susceptible to slight 

 degrees of acidity. In order to destroy them without injuring the yeast the 

 temperature is arranged so that the lactic acid bacteria can develop ; the 

 optimum temperature of the lactic acid bacteria is from 47 to 50° C, that 

 of the butyric acid organisms about 40° C. The mash is hence kept at a 

 temperature of about 50° C, whereby the lactic acid bacteria thrive and the 

 formation of lactic acid effectually prevents the development of the butyric 

 acid organisms. When the acid present reaches i-o to i-i per cent., the 

 process is stopped by raising the temperature to 70° C. ; the mash is re- 

 cooled to 20° C. and pitched with yeast, in the proportion of about lib. to 10 

 gallons ; after about 14-16 hours the yeast has so far developed as to be used 

 in the main process, a portion being kept for the next sour mash. 



This process left much to chance, and has been developed on other lines, 

 although the object in view has always been the same. In the first place the 

 presence of lactic acid bacteria is adventitious, and, although their presence is 

 very general, it not infrequently happened that the process miscarried by 

 reason of their absence. To get over this difficulty the infection of the sour 

 mash was carried out by inoculation with pure cultures of lactic acid bac- 

 teria, and now more recently a new procedure known as the hydrofluoric 

 acid process has been largely introduced. 



It was sought for a long time to find some substance that would be anti- 

 septic to the butyric acid bacteria and yet harmless to the development of 

 yeast, and after many bodies had been tried Effront, in 1890, introduced the 

 use of alkaline fluorides. The initial proposition was to add from 4 to 8 grms. 

 of hydrofluoric acid per hectolitre (say from ^V to ro ^^- P^r 100 gallons) of the 



