BEER 



219 



mentations may be set up by various bacteria, yeasts and mold, 

 causing more or less serious spoiling and even complete deteriora- 

 tion. The following are the more common beer diseases which 

 may be brought to the attention of the food bacteriologist. 



a. Ropiness. — This is quite common. The beer becomes thick 

 and mucilaginous capable of being drawn out into threads. Two 

 species of bacteria cause ropy beer; Bacillus viscosus I and B. 



Fig. 74. — Saccharomyces cerevisecB. The variety known as brewers' top 



yeast. — (Oberhefe.) 



viscosus II. These bacteria are rod-shaped and measure 0.8 by 

 1.6-2.4 microns. Bacillus I gives rise to yellowish-white viscous 

 patches on the surface of the beer whereas bacillus II does not 

 develop such patches. B. viscosus III has been isolated from 

 British ropy beer. The ropiness results from a change in the cell- 

 wall of the bacterium and not from any chemical change in the 

 beer itself. Ropiness may also be caused by a mold, Dematium 



