THE MANUFACTtTRE OF VINEGAR 543 



Before starting the acetic fermentation, it is a usual and good 

 practice to add about 10 per cent of good vinegar to the liquid, which is 

 thus rendered acid and therefore less liable to alteration by injurious 

 bacteria and other microorganisms. 



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 Cultitres. — 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 jyater, filtering and adding the proper 

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

 apration, 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 

 hquid. 



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. 



Domestic Method. — ^A cask of convenient size (40 to 200 liters) is 

 fitted as illustrated in Fig. 142. 



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 



