258 MICRO-ORGANISMS AND FERMENTATION. 



" yeast bite." Frew observed that the " stench " in English 

 beers, which have undergone secondary fermentation, due to 

 sulphuretted hydrogen or a similar substance, is derived from 

 a special wild yeast, Sacch. foetidus I. It is well known in 

 practice that 8. ellips. II. and other species can produce- 

 diseases even when the beer is first infected in the storage 

 casks, transport casks, or bottles. Reference must be made 

 to the fact that mixtures of culture yeasts, each capable of 

 producing a good product, may, according to Hansen, produce 

 diseases in beer. By the use of mixtures for the pitching 

 yeast it was found that the species present in smaller quantity 

 rendered the beer more liable to turbidity, in comparison with 

 fermentation carried on with the leading species alone. Even, 

 when the two species were separately applied, and the beers 

 mixed for the first time in the storage casks, similar phenomena 

 were observed. 



Pichi has found species producing disease in wine. 



In the storage casks of lager beer, Lafar found a budding 

 fungus of the Mycoderma type, which produced acetic acid. 



Just as the moulds react differently upon various carbo- 

 hydrates, so it has been shown by the exact researches of 

 Hansen and others that the yeasts exhibit pronounced char- 

 acteristics. In addition to the true Saccharomycetes, Myco- 

 derma cerevisice, Sacch. apiculatus, the Torulas, and Monilia,. 

 are reviewed in the following paragraphs : 



Hansen's six Saccharomycetes (Sacch. cerevisice I., Sacch.. 

 Pastorianus I., II., and ///., Sacch. ellipsoideus I. and II.)- 

 behave as follows : They all develop invertase ; they convert 

 saccharose into invert sugar and ferment the latter ; they 

 ferment maltose and dextrose, but not lactose. All the 

 bottom yeasts used in practice react similarly with these 

 four sugars. 



Sacch. Marxianus, Sacch. iMdwigii, and Sacch. exiguus do 

 not ferment maltose and lactose ; they invert saccharose and 

 ferment nutritive solutions of invert sugar and dextrose. 



Sacch. membrancefaciens and Mycoderma cerevisice possess 

 no inverting enzyme, and do not ferment any of the four 

 sugars. 



Sacch. apiculatus does not invert saccharose, and of the 



