112 BACTERIA AND FERMENTATION 



Bacillus viscosus vini. This latter organism occurs in the form of 

 small rods, frequently united in pairs, and capable of producing 

 ropiness in white wines in the absence of air. The presence of sugar 

 is a sine quA non for the occurrence of the malady, since it forms the 

 material from which the strings of mucus are produced. Nessler 

 maintains that wines containing over 10 per cent, of alcohol are proof 

 against ropiness. 



Pasteur also investigated ropiness in beer, and traced it to 

 Micrococcus viscosus. But in all probability there are a number of the 

 ScMzomycetes possessing the power of rendering beer and wine viscid. 

 The so-called Sarcina turbidity of beer has been traced to the Pedio- 

 coccus cerevisice. But it should be borne in mind that such conditions 

 may be easily mistaken for turbidities set up in other ways. 



3. Changes in Colour. — The browning of wines — changing of 

 colour with turbidity and unpleasant flavour, sometimes occurring in 

 white wines — is said to be due to oxydaxes, enzymes produced by 

 some of the yeasts and setting up an oxidation. 



4. Alteration of Flavour, Bitterness, Acidity, etc. — Bitterness 

 of wine almost exclusively affects red wines. The wine decolorises 

 and develops a strange odour and a bitter after-taste. Pasteur 

 attributed the disease to bacteria, but up to the present no species 

 has been isolated able to bring about this condition upon inoculation 

 in healthy wines. Bittering of beer may be occasioned by a disease- 

 yeast {Saccharomyces pastorianus I.) introduced at the commencement 

 of the primary fermentation, even in such small quantity as one-fifth 

 of the pitching yeast. This organism, according to Hansen, not only 

 injuriously affects the taste and odour of the beer, but also its 

 stability. It is of very frequent occurrence in breweries. 



The turning (tourne) of wines is by no means a clearly-defined or 

 uniform phenomenon. The most frequent form, perhaps, is that due 

 to the vinegar taint (caused by Mycoderma aceti). But the condition 

 may be set up by the lactic acid bacteria. It mostly attacks young 

 vintages. The wine becomes turbid, eventually having an appearance 

 of diluted milk, and even later it may assume a condition of brown 

 or inky-black liquid. 



The turning of beer, on the other hand, is a simple malady due 

 to lactic acid fermentation, set up by the Saccharo-hacillus pastorianus 

 HI. The beer at first loses its brightness, then becomes turbid, and 

 ultimately, according to some authorities, of unpleasant smell and 

 taste. If the sample be shaken delicate waves or films of the organ- 

 ism are apparent to the naked eye, and eventually the beer becomes 

 muddy. Hansen has shown that there are two species of yeast, S. 

 pastor. III. and S. ellipsoideus II., which produce the disease when 

 they are present in the pitching yeast, and are, therefore, introduced at 

 the commencement of the primary fermentation. Both species are 



