24 ENCYCLOPEDIA OF PRACTICAL HORTICULTURE 
and the quality of his water, yeast, and 
fermentable materials, his yields of alco- 
hol may approximate those indicated or 
may, on the other hand, fall far below it. 
Nature of Yeast 
Yeast, the exciting agent of the alco- 
holic fermentation, is familiar to the gen- 
eral public chiefly in the form of the 
small square cakes which are sold at 
groceries, and to workers in breweries 
and distilleries as a more or less frothy 
paste. Whatever its outward form and 
appearance may be, it always is made up 
of innumerabie microscopic plants which 
are globular or ovoid in form, approxi- 
mately 1/4000 inch in diameter, and fairly 
colorless and transparent as seen under 
the microscope. Yeast withstands pro- 
longed exposure to cold without serious 
injury, but is weakened rapidly when 
kept at high temperatures, and is killed 
quickly when heated to about 110 degrees 
Fahrenheit. It ordinarily reproduces it- 
self by a process of budding, and grows 
at the expense of various nutrient ma- 
terials, such as lime, potash, phosphoric 
acid, and nitrogenous compounds, which 
it absorbs from the solutions in which it 
is placed. The vigor of a fermentation 
seems to depend largely upon the phenom- 
enon of yeast growth. Good fermentation 
can not be established without abundant 
and suitable nutrients for the yeast and 
its vigorous development. 
The selection of a suitable yeast for 
any purpose and its preparation and 
maintenance in a pure and vigorous condi- 
tion are arts which demand thorough 
taining and experience. They can not 
be learned from books alone and call for 
no small amount of manipulative skill. 
Preparation of Saccharine Solutions for 
Fermentation 
Certain saccharine materials, such as 
the juices of most fruits and of the sugar 
cane, are in their natural condition so 
susceptible to fermentation that they can 
not be preserved unaltered unless they 
are sterilized in sealed bottles or some 
antiseptic or preservative material, such 
as salicylic acid, is added. Other sugar- 
containing materials, such as molasses, do 
not ferment readily until they have been 
subjected to certain preliminary treat- 
ments. Thus, both cane-molasses and beet- 
molasses must be diluted with water be- 
fore they can be fermented, and since 
they often are deficient in the nitrogen 
compounds which are essential to yeast 
production it sometimes is found neces- 
sary to add nitrogen to their solutions in 
the form of ammonium sulphate or some 
equivalent material. Furthermore, beet- 
molasses is usually alkaline, and as yeast 
will not work in alkaline solutions it is 
necessary to acidify beet-molasses before 
adding yeast to it. Diluted sulphuric acid 
is commonly used for this purpose. The 
amount of water or of chemicals which 
must be added to a given quantity of mo- 
lasses to fit it for fermentation will de- 
pend upon the composition of the latter. 
Experience has shown that with ordinary 
cane-molasses it is desirable to use about 
six volumes of water for one of molasses. 
In this way a solution is obtained which 
contains about 12 per cent of sugar and 
is capable of producing approximately 6 
per cent of alcohol. This proportion of 
sugar has been found, in general, to give 
the best results with regard to the rate, 
completeness, and economy of fermenta- 
tion. 
Preparation of Fermentable Solutions 
from Starchy Raw Materials 
While the saccharine raw materials of 
the fermentation industries can be pre- 
pared Ior use by the relatively simple 
processes of solution or juice expression, 
such materials as potatoes and grain, 
which contain little sugar and much 
starch, must be subjected to special treat- 
ment in order to convert the insoluble and 
unfermentable starch into sugar. The 
series of operations by which this starch 
conversion is accomplished is called 
“mashing,” and consists of a preliminary 
scalding or cooking process, the purpose 
of which is to liquify the starch, and of 
the saccharification proper, in which the 
soluble starch is converted into dextrin 
and sugar. The agency by which the 
latter conversion is accomplished is the 
specific action (in the presence of mois- 
ture, and at a suitable temperature) of 
