BEER 



221 



(aeration) is more favorable than in the bottom fermented beers. 

 The three most common and best known beer acidifiers are Bac- 

 terium aceti, B. pastorianus and B. kutzingianum. 



Lactic acid and butyric acid bacteria may gain access to the 

 fermenting vats and render the beer wholly unfit for use. Of 

 these two kinds of bacteria, the butyric acid formers are by far the 

 most objectionable because of the very disagreeable odors^ which 

 they form. 



&. ^& &fi??&>>~~. 



FIG. 76. Saccharomyces ellipsoides. The common wine ferment. Also common in 

 jams, jellies and canned fruits. 



c. Bitterness. Bitterness of beer may be caused by several 

 species of so-called wild yeasts, principally Saccharomyces pastori- 

 anus I, II and III, and of these, variety I is the most common and 

 most injurious. It is stated that small amounts of varieties 

 II and III are not objectionable as they transmit to the beer a 

 stronger taste and smell. 



d. Turbidity. Turbidity of beers may be the result of a 

 variety of factors which may be outlined as follows. 



