458 MICROBIOLOGY OP SPECIAL INDUSTRIES. 



times or through an equal number of vats before it is completely 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. 



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 amount of solids and extractive matter they con- 

 tain. This coats 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 

 beech chips and half filled with the liquid to be acetified. By rotating 

 the barrel at short intervals the liquid trickles repeatedly over the chips 

 and with proper aeration, the acetification is rapid and complete. 



AFTER-TREATMENT. Alcohol vinegars require little treatment. They 

 should be filtered and are usually colored slightly with caramel. Being 

 little more than dilute solutions of acetic acid without ethers or bouquet, 

 there is no object in aging them. 



Wine and cider vinegars, for the best results, require aging and careful 

 treatment. They should be filtered and pasteurized as soon as made and 

 stored hi clean casks which are well bunged and kept constantly full in a 

 cool place of even temperature. If too dark in color they may be decolor- 

 ized with pure animal charcoal carefully extracted with acids and water. 



Before using or bottling, the vinegar should be fined with isinglass. 



