146 MICRO-ORGANISMS AND FERMENTATION. 



of infection lies in the pitching-yeast. These diseases have 

 led to very great difficulties and have caused considerable 

 losses in breweries. Hansen's observations on the disease 

 yeasts have been confirmed by Gronlund, Will, Lasche, 

 Kokosinsky,Krieger, Windisch, and P.Lindner, and extended 

 by new examples. The wild yeasts can also bring about 

 disturbing-effects in top-fermentation breweries. For instance, 

 the so-called " summer-cloud " of Australian beers is caused, 

 according to de Bavay, by a wild Saccharomyces species. 

 This organism causes turbidity and imparts to the beer an 

 acid, bitter taste. 



Eecently Pichi has also detected disease-yeasts in wine. 



Just as the mould-fungi exhibit a different behaviour 

 towards the carbohydrates (see Penicillium, Mucor, Monilia), 

 so the different Saccharomycetes and similar fungi have been 

 shown by Hansen's comprehensive investigations to also 

 exhibit pronounced characteristics in the same direction. 

 In addition to the true Saccharomycetes we will here also 

 review Mycoderma cerevisice, Sacch. apiculatus, the Torula 

 forms, and Monilia. 



Hansen examined the behaviour of a large number of 

 Saccharomycetes towards the four carbohydrates saccharose 

 (cane-sugar), maltose, lactose, and dextrose. 



His known six species of Saccharomycetes (Sacch. 

 cerevisice L, Sacch. Pastorianus L, IL, and ///., Sacch. 

 ellipsoideus I. and //., see page 159) behave as follows: 

 They all develop invertase ; they convert cane-sugar into 

 invert-sugar, which they then ferment ; they ferment maltose 

 and dextrose, but not lactose. All the bottom-yeasts used in 

 practice show the same behaviour towards the four sugars 

 mentioned. 



Sacch. Marxianus (page 176), Sacch. Ludivigii (page 

 179), and Sacch. exiguus (page 176) do not ferment maltose 

 and lactose ; they invert saccharose and ferment nutritive 

 solutions of invert-sugar and dextrose. 



Sacch. membranaefaciens (page 177) and Mycoderma 



