276 The Potato 



tiire most favorable to fermentation is between 60° and 70° F., depend- 

 ing on the weather conditions and vokmie of the mash. At the same 

 time the mash is run through the fermenter the yeast mash (about 

 3 per cent by volume of the main mash) is also added. It is prepared 

 in a tube above the fermenter and can be dropped into it. 



Fermenting the mash. — After the yeast and mash are in the fer- 

 menter, the process of fermentation will begin and the sugar in solu- 

 tion will be broken down into alcohol and carbon dioxide gas. The 

 gas goes out into the air, and the alcohol remains. At this point, 

 it is important to know the gravity and acidity of the "set mash" — 

 as it is now called. The specific gravity indicates the amount of 

 sugar and is ascertained as follows : Stir mash and filter small por- 

 tion through cheesecloth into a cylinder. A Balling saccharimeter is 

 placed in the filtered liquid. Tlie reading at the level of the liquid 

 should be 16° to 18°, showing that the mash contains 16 to 18 per 

 cent of solids, most of which is sugar. The acidity of the set mash is 

 determined by neutralizing a small portion of the mash in a normal 

 solution of sodium hydroxide, and the amount of the latter required 

 will represent the acidity of the mash. It is done in the following 

 way : 20 cubic centimeters of the filtered liquid is placed in a beaker 

 and the sodium hydroxide is slowly dropped in from a burette until 

 the filtered liquid has been neutralized and will not turn blue litmus 

 red or red litmus blue. The number of cubic centimeters of sodium 

 hydroxide used will represent the acidity of the mash. After the mash 

 has been set for ten or twelve hours, the fermentation will become 

 vigorous and the temperature will rise. It should not be allowed 

 to go above 80° F. or much of the alcohol will evaporate. To keep 

 the mash cool, a coil with cold water passing through it is slowly 

 raised and lowered through the mash. The fermentation is allowed 

 to continue at a temperature of 60° to 80° F. for 72 hours. The 

 gravity should fall and the acidity remain about the same dm"ing the 

 process. The tests should be made every 24 hours. If the acidity 

 rises too much, the fermenters are scrubbed clean with a 5 per cent 

 solution of formalin or other disinfectant. This will clean out the 

 butyric acid which often is the cause for raised acidity. 



Distilling the alcohol. — In Fig. 27 is shown a distilling apparatus 

 adapted for the economic separation of alcohol from the mash. It 

 is not complicated, as one would think at a first glance, but is very 

 simple. The fermented mash is slowly pumped into a distilling ap- 

 paratus, where it is brought into contact with live steam, which boils 



