264 DFXOMPOSITION 



In wine- and beer-making, as in the manufacture of 

 alcohol, the production of alcohol is the essential result. 

 The CO2 is valuable in the manufacture of beer and in 

 the production of champagne and other " sparkling ** 

 wines. The alcohol itself produced being a partly oxidized 

 compound, can be further oxidized by burning; this may 

 be done in the body, in a lamp, or in an engine, or by 

 bacteria. In the first three cases the result is complete 

 oxidation and the production of CO2 and H2O and energy. 



C^H.OH + 3O2 = 2CO2 + 3H2O 



alcohol 



Acetic Fermentation. — In the last case, oxidation 

 by bacteria, oxidation is incomplete, 



C2H5OH + O2 - CH3COOH + H2O 



alcohol acetic acid 



the products being acetic acid — familiar to us in vinegar 

 — and a certain amount of energy, some of it recognizable 

 as heat. If the action of the bacteria is allowed to con- 

 tinue the result will be the oxidation of the acetic acid 

 to CO2 and HoO and the liberation of the rest of the 

 energy. 



The Souring of Milk. — This process, involved in 

 the manufacture of many foods and drinks, has also been 

 carefully studied on account of its technical and com- 

 mercial importance. Cow's milk, as well as the milk of 

 other animals, contains a sugar of the same proportional 

 formula as cane and malt sugars, called milk sugar, sugar 

 of milk, or lactose — Ci.HaaO,,, which may be acted upon 

 by many different organisms, both large and small. When 

 milk is digested or acted upon by certain bacteria or by 

 certain yeasts, it sours, a curd forms, and the butter fat 

 may be separated off. The reaction, so far as the sugar 

 is concerned, consists in the splitting of the lactose mole- 

 cule into four molecules of lactic acid because of the 

 action of the bacterial enzym known as bacterial zymase. 



C,2H,20n + H2O = 4C3HeO, 



