THF MANUFACTURE OF VINEGAR 641 



All the processes of vinegar-making depend on the same principle, 

 which is to expose the liquids prepared as above to the action of acetic 

 bacteria with full access of atmospheric oxygen at a suitable tem- 

 perature. The rapidity of the process depends on the number of 

 active bacteria present, the nutritive value of the liquid, the tem- 

 perature, and especially on the free access of oxygen. 



STARTERS AND PURE CULTURES .--The 10 per cent of vinegar added 

 to the liquid to be fermented usually contains sufficient bacteria to in- 

 sure a prompt start. Where this is not the case, a starter may be 

 prepared by exposing a suitable liquid in a shallow vessel to the air of a 

 warm room for several days. Any liquid containing about 4 per 

 cent of alcohol, 2 per cent of acetic acid and a moderate amount of 

 nitrogenous matter is suitable. A decoction made by boiling 50 g. 

 of fresh yeast in 1,000 c.c. of water, filtering and adding the proper 

 amount of vinegar and wine or beer will serve. After thorough 

 aeration, such a liquid in a few days becomes covered with a film of 

 acetic bacteria. This film may be used as a starter by gently submerg- 

 ing the vessel in which it is formed in the liquid to be acetified, or by 

 removing with a clean sliver of wood which is afterward floated in the 

 liquid. 



In practice, such a starter gives a sufficiently pure fermentation of 

 acetic bacteria. The particular species of acetic bacteria, however, is 

 left to chance. Pure cultures of a particular selected form would in all 

 probability improve the certainty of the production of good vinegar, 

 but the method has not entered into general practice. 



APPARATUS. Most metals of all kinds should be avoided as much 

 as possible. The hoops of barrels and buckets may be protected by a 

 coating of paraffin. Pumps may be of wood or of the special alloys al- 

 ready mentioned, or they may be so constructed that they will not come 

 in contact with the liquids. 



METHODS 



DOMESTIC METHOD. A cask of convenient size (40 to 200 liters) is 

 fitted as illustrated in Fig. 159. 



The wine or cider to be acetified, after filtering, if necessary, is 

 poured into the cask until it is about one-half to two-thirds full, the 

 object being to have as large a surface as possible for the growth of the 

 bacterial film. Free circulation of air is insured by a 5-cm. hole in 

 each head of the cask, one near the surface of the liquid and one near 



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