BREWERY YEASTS. 317 



hat-shaped or lemon-shaped ; in the last two cases provided 

 with a distinct projecting rim ; otherwise smooth. They have 

 only one membrane ; germination takes place by budding. 

 The majority of species are distinguished by the formation of 

 esters ; a few do not bring about fermentation. 



GENUS V. Pichia E. C. Hansen. 



The spores hemispherical or irregular and angular. No- 

 fermentation ; strong growth of mycelia. 



GENUS VI. Willia E. C. Hansen. 



Spores hat-shaped or lemon-shaped with distinctly pro- 

 jecting rims. The majority produce esters vigorously ; a few 

 produce no fermentation. 



B. DOUBTFUL SACCHAROMYCETES. 

 Monospora. Nematospora. 



The genus Schizosaccharowyces cannot be included in the 

 family of Saccharomycetes. 



1. THE SPECIES USED INDUSTRIALLY (CULTURE YEASTS). 



(a) Brewery Yeasts. 



According to the physical phenomena of fermentation, a 

 distinction is made between low- and high-fermentation yeasts, 

 both in the brewery and elsewhere. The low-fermentation 

 yeasts gradually collect during fermentation to form a deposit 

 in the fermenting liquid, whereas the top-fermentation yeasts, 

 in the normal course of fermentation, partly form a layer on 

 the surface of the liquid, differing in character and thickness 

 according to the race, and partly form a deposit. The two 

 kinds of yeasts in the brewery impart a different character 

 to the fermented liquor. This has been established by parallel 

 experiments with wort of identical composition. The two 

 groups of yeast may, therefore, be said to exhibit a different 

 form of chemical activity. Bau has proved that most of the 

 known species of low-fermentation yeasts ferment melibiose. 

 whilst some of the top yeasts are incapable of fermenting it. 



