426 



MICROBIOLOGY OF SPECIAL INDUSTRIES. 



is a very fine short rod which does not unite in filaments. It attacks 

 the sugar, especially the levulose, producing volatile acids and mannit. 

 The latter may reach over 2 per cent and the former 5 per cent, 

 giving a sweet-sour wine which is completely spoiled. 



The bacteria grow abundantly only at high temperatures approaching 

 40 and can be controlled by cool fermentation, increase of acidity and 

 proper use of sulphurous acid. 



Butyric Bacteria. In the cooler climates, wines, especially old red 

 wines in bottles, often become bitter. This trouble is due to comparatively 

 large rod-shaped bacteria, first described by Pasteur. The cells re- 

 main united in angular filaments, short at first, but becoming longer 

 and finally thicker with age by incrustations of coloring matter. 



\ 



L 

 ^A 



/ 

 J> 



FIG. 87. Bacteria of wine diseases. A, bacteria of "turned wine," young wine 

 (After Bioletti); D, bacteria of "turned wine," old wine (After Bioletti}; C, mannitic 

 bacteria (After Maze and Pacottet); D, bacteria of "bitter wine" (After. Pacottef}. 



The tannin, coloring matter, and glycerin of the wine are attacked, 

 acetic and butyric acids being formed. In small amounts the bacteria 

 do little or no harm, in larger amounts they may spoil the wine. Means 

 which increase the alcohol, tannin and acidity diminish the liability to 

 the disease. Prompt attenuation and clarification and in extreme cases 

 pasteurization will cure wines not too badly affected. 



All the aboye anaerobic bacteria of wine diseases probably exist in 



most wines. Which develop most, or whether any develop sufficiently 



to injure the wine depends on conditions, chiefly the composition of the 



must and the temperature at which the wine is fermented or stored. 



Most diseased wines show a mixed infection of several forms. 



