138 PROCEEDINGS OF SECTION B. 
per cent. of the theoretical yield of alcohol was obtained. 
The method is now used in the Belgian distilleries; but, in- 
stead of Roux, a more energetic variety—Mucor B, or 
Belgian koji—is employed. One gramme (15 grains) of 
Mucor suffices for 25 tons of grain, thus replacing three tons 
of malt, and saving a loss of six cwts. of starch, which is 
equivalent to 44 gallons of pure alcohol. 
The yeasts and moulds, however, are not the only micro 
organisms that can saccharify and ferment. Some bacteria 
ferment starch to alcohol, and others ferment sugar. An 
example of the latter is Bact. coli commune, a common in- 
testinal bacterium, which ferments one-sixth of the glucose 
in the medium to common alcohol. 
Yeasts and Y easts. 
In the wine industry, moulds are also used, but this is 
done unwittingly, and much bad wine could be traced to 
their agency. Those fermented beverages which contain the 
original juice of the fruit, or extract of the grain, and in the 
fermentation of which it has been the custom to employ 
yeast, cannot have the yeast replaced either partly or entirely 
by moulds, because these produce substances which are dis- 
agreeable to the palate. I use the word yeast with all due 
caution, because there are yeasts and yeasts, some of which 
are as objectionable as moulds. It is a common idea that 
all yeasts ferment, and therefore any yeast is good enough 
to produce alcohol. That is quite right, and also quite 
wrong. There are species of yeasts—and of these species 
there are varieties, and of these there are races—and there 
is as much difference between the races of yeasts as between 
the races of mankind. If we take, for example, the culti- 
vated yeast of the brewer (Saccharomyces cerevisiae), we 
find that it can be divided into top and bottom varieties, the 
former rising to the top of the wort during fermentation, 
and the latter remaining at the bottom of the fermenting 
vat. These, again, can be subdivided into races, each of 
which will have a different effect upon the finished beer. 
There are possibly as many races of Sacch. cerevisiae as there 
are breweries. 
The Route of Brewing. 
The brewer is a happy mortal. He kills the bacteria in 
his mash by boiling, and adds hops, the essential oil and 
extractive matters of which hinder the subsequent growth of 
bacteria. He can, if he desire, add to his wort a pure 
culture of yeast, so that he has everything under control. 
He knows the composition of his wort, and can attemperate 
