BACTERIA 37 



3. Fermentative Bacteria. Among the important fermen- 

 tative bacteria are: 



(a) Acetic (vinegar). 



(6) Lactic (milk). 



(c) Butyric (butter). 



(a) Acetic Bacteria. The so-called "mother" of vinegar 

 is composed of thousands of these bacteria. They convert 

 the alcohol (C 2 H 5 OH) into acetic acid (CH 3 CO.OH) as 

 follows : 



CzHsOH + O 2 + acetic bacteria = CHsCO.OH + H 2 O. 



The reaction is an oxidation process. 



(6) Lactic Bacteria occur in milk. They turn milk sour 

 by changing lactose or milk sugar (C^H^On) into lactic acid 

 (C 3 H 6 O) 3 as follows: 



C, 2 H 22 On + H 2 O + lactic bacteria = 4CsH6Os. 



This lactated milk forms an important part of the diet 

 of some nations. In the United States it is used as a beverage, 

 the acid or tart taste of the milk being due to the lactic acid. 



(c) Butyric Bacteria occur in butter. Butyric bacteria 

 break up the lactic acid formed in the lactic fermentation 

 as follows: 



2C 3 H 6 O 3 + butyric bacteria = CsHvCO-OH + 2CO 2 + 2H 2 . 



4. Cheese Bacteria. Several of the most important sapro- 

 phytic bacteria are used in the manufacture of cheese. These 

 bacteria live upon the solid constituents of milk, forming 

 colored products of excretion and odorous compounds which 

 give the color, flavor and odor to cheese. There are as many 

 types of cheese bacteria as there are varieties of cheese. The 

 most important of these are American, Swiss, Roquefort, 

 Limburger, Gorgonzola, Brie, Stilton, Camembert, Chedder 

 and Edam cheese. 



