58 BIOLOGY AND TECHNIQUE 



or scum which is popularly known as the "mother of vinegar." 

 Destruction of these bacteria by disinfectants or by sterilization 

 with heat promptly arrests the process of vinegar formation. 

 Chemically, the conversion of the alcohol consists in a double oxida- 

 tion through ethyl aldehyde into acetic acid as shown in the follow- 

 ing formulae : 



1. C 2 H 5 (OH) + = CH 3 (COH) 

 Alcohol Ethyl aldehyde 



2. CH 3 (COH) + O = CH 3 (COOH) 

 Acetic acid 



Alcoholic Fermentation (Zymase). The formation of alcohol as 

 an end product of fermentation is of great importance in a number 

 of industries, primarily in the production of wine and beer. 

 While accomplished by a number of bacteria, this form of fermen- 

 tation is carried out chiefly by the yeasts. 



Expressed in formulae the simplest varieties of alcoholic fermen- 

 tation, from mono- and disaccharids, may be represented as follows : 



C 6 H 12 6 == 2C 2 H 5 (OH) + 2C0 2 

 Dextrose Ethyl alcohol 

 or 



C 12 H 2 Ai + H 2 = 4C 2 H 5 (OH) + 4C0 2 

 Saccharose Ethyl alcohol 



In all cases the process may not be so simple as indicated by the 

 equations, since by-products, such as higher alcohols, glycerin, suc- 

 cinic and acetic acids, may often be found in small traces among 

 the end-products of such fermentations. The conditions which favor 

 alcoholic fermentation by the yeasts are extremely important, since, 

 upon observance of these, depends much of the uniformity of result 

 which is so desirable in the industries mentioned above. The opti- 

 mum concentration of sugar for the production of the highest quan- 

 tity of alcohol is at or about 25 per cent. The temperature favoring 

 the process ranges about 30 C. Under such conditions fermenta- 

 tion may continue until the alcohol forms almost a 20-per-cent 

 solution. Most of the fermentations important in the wine, beer, 

 and spirit industries, take place under anaerobic conditions, since 

 the carbon dioxide which is formed soon shuts out any excess of air. 



