198 AGRICULTURAL BACTERIOLOGY 



the entrance of flies, these holes should be screened with 

 thin cloth or with wire netting that has been varnished so 

 that the iron will not be attacked by the acetic acid. The 

 addition at the start of a small quantity of vinegar, or bet- 

 ter some of the mother of vinegar, serves to seed the liquid 

 with the necessary acetic bacteria. The fermentative proc- 

 ess progresses rather slowly at first, but in a few months 

 the vinegar will be ready for use. If it is desired to con- 

 tinue the process in the same barrel, fresh alcohol can be 

 added through the bung-hole by means of a glass funnel 

 to which a rubber tube is attached. This enables the alco- 

 hol to be added without disturbing the bacterial film on the 

 surface. 



Temperatures between 65 and 75 F. are most favorable 

 for both alcoholic and acetic fermentation. At much lower 

 temperatures the alcohol is produced so slowly that unde- 

 sirable organisms have opportunity for growth. When the 

 acetic fermentation is complete, it is desirable to protect 

 the acid from the action of organisms that would destroy it. 

 This can be done by storing it in completely filled and 

 closed containers, for all harmful organism will be of the 

 aerobic group. 



Under the best of conditions the oxidation of the alcohol 

 to acetic acid will require a long period in the method de- 

 scribed, since the growth of the organism is confined to the 

 surface of the liquid. In the manufacture of distilled vine- 

 gar, the oxidation process is hastened by providing a much 

 extended surface for the growth of the bacteria and by pro- 

 viding for a constant supply of air to the organisms. 

 These conditions are secured by filling large conical tanks 

 with beech shavings that have been extracted with water 

 and with vinegar. The tank has a false bottom containing 

 numerous holes for the passage of air, which enters the 

 tank through holes in its side below the false bottom. 



