386 PHARMACEUTICAL BOTANY 
There are two varieties of brewer’s yeast, viz.: Tor YEAsts 
and Bottom Yeasts. ‘Top yeasts grow on or near the surface 
of the liquid and produce rapid fermentation at summer tem- 
peratures causing great quantities of carbon dioxide to arise to 
the surface and thus forming the froth which is characteristic of 
ale, stout and porter. They tend to remain attached in clusters. 
Most of the yeasts used for compressed yeast and bread making 
are top yeasts. 
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Fic. 286.—Saucer-shaped fruit-bodies of Peziza repanda. (Harshberger, from Photo 
by W. H, Walmsley.) 
A 
Bottom yeasts grow at about 4°C. at or near the bottom of 
the vat. They are used in the manufacture of lager beers. | 
Compressed yeast (Cerevisiae Fermentum Compressum) or 
“yeast cake” consists of the moist, living cells of Saccharomyces 
cerevisie or of other species of Saccharomyces, combined with a 
starchy or absorbent base. 
Yeast contains the antineuritic vitamin B, and the pellagra 
preventive vitamin B, or G. 
OTHER YEASTS.—Saccharomyces ellipsoideus (Fig. 285) is a wild 
species, several varieties of which are found growing on grapes 
especially in districts where wine is produced. It is termed 
the true wine yeast to distinguish it from other wild species 
found in grape juice, like S. apiculatus and S. membranifaciens 
