646 MICROBIOLOGY OF ALCOHOLIC FERMENTATION 



supply is accomplished by various automatic devices. If the supply is 

 continuous, the liquid tends to run in streams or currents in certain 

 parts of the vat and much of the acetifying surface is lost; if too rapid, 

 the bacterial film is removed from the upper part of the mass of beech 

 chips and only the lower part is effective. 



From the false head, the liquid passes through numerous small holes 

 to the mass of beech chips, over which it trickles slowly and is acetified 

 by means of the bacterial film which covers them. By the time it 

 reaches the lower false head, the alcohol is in greater or less amount 

 converted into acetic acid. Usually the liquid must pass through from 

 two to five times or through an equal number of vats before it is com- 

 pletely changed into vinegar. The number of passages depends on the 

 amount of alcohol present, the height of the acetifying column, the 

 rapidity of the flow, the temperature, and on the perfection of the 

 apparatus. 



Oxygen is supplied by the air which, entering holes in the vat below 

 the lower false head, passes through numerous holes in the latter, 

 through the interstices between the chips and out through short tubes 

 fixed in the upper false head and holes in the top. The passage of air 

 is insured by the heating of the interior due to the fermentation. It 

 can be regulated by the number and diameter of the air holes. 



The temperature, which should be close to 30, must be carefully 

 regulated. If the temperature rises too high, the loss by evaporation 

 will be much increased; if it remains too low the acetification will be 

 retarded. Too low a temperature is less injurious than too high a 

 temperature. 



Many modifications of this method exist, having principally for 

 their objects the more complete regulation of the temperature and air 

 supply, the recuperation of the volatile matters, and the avoidance of 

 the need of repassing the liquid through different acetifying columns. 



ROTATING BARRELS. Several methods are in use which attempt to 

 combine the rapidity of the German machines with the quality of the 

 Orleans method and which are suitable for use with wine and cider. 

 These liquids cannot be acetified conveniently by the German method 

 on account of the large amounts of solids and extractive matter they 

 contain. These coat the beech chips rapidly and interferes with the 

 perfect working of the machine. 



These methods make use of a barrel filled partially or wholly with 



