TAXONOMY 
203 
There are two varieties of brewer’s yeast, viz.: Top yeasts and 
Bottom yeasts. Top yeasts grow on or near the surface of the liquid 
and produce rapid fermentation at summer temperatures causing 
great quantities of carbon dioxide to arise to the surface and thus 
forming the froth which is characteristic of ale, stout and porter. 
Bottom yeasts grow at about 4°C. at or near the bottom of the 
vat. They are used in the manufacture of lager beers. 
Fig. 83 . — Saccharomyces cerevisea. The form or variety known as brewers' top 
yeast. ( Oberhefe .) 
Compressed yeast (Cerevisue Fermentum Compressum) N. F. 
consists of the mosit, living cells of Saccharomyces cerevisice or of other 
species of Saccharomyces, combined with a starchy or absorbent 
base. 
Saccharomyces ellipsoideus 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 
