156 FLAVORING AND BEVERAGE PLANTS 
uents. A small amount of a tannin-like substance is found 
also in coffee, and in cacao. Cacao, although used as a bev- 
erage, is so nutritious that it should be regarded rather as a 
food than as a food-adjunct. 
58. Alcoholic beverages and stimulants in general. Alco- 
holic beverages are either fermented or distilled. 
Fermented beverages include beers or malt liquors, and wines. 
Beer, as already stated (sections 19 and 29), is made by fer- 
menting a sweet liquid obtained chiefly from barley malt. In 
much the same way that the diastase in the sprouting grain 
changes the starch into sugar, an enzyme contained in the yeast 
which is added to the sweet malt liquid, changes its sugar 
into alcohol and the gas known as carbon dioxid. Yeast 
is a plant consisting of exceedingly minute bodies of the form 
shown in Fig. 151. These multiply very rapidly under 
favorable conditions of food supply and temperature. Hence 
a small amount of yeast added to a vat full of malt liquid 
soon becomes a considerable quantity. When the fermenta- 
tion is well under way the liquid is put into air-tight kegs or 
bottles so that the gas produced may be retained. When 
the beer is poured out this gas rises to the surface and forms 
bubbles of foam. After the sugar is converted into alcohol 
and carbon dioxid gas, the aleohol may be turned into acetic 
acid (the acid of vinegar) by a plant similar to yeast (see 
Fig. 152) unless its action is prevented. This is accomplished 
mainly by the addition of hops (Fig. 153) which at the same 
time impart their peculiar flavor to the beer and give it a 
bitter taste. The preservative action as well as the flavor of 
the hops is due chiefly to a volatile oil of which the fruit con- 
tains about 1%. The stupefying effect of beer is also believed 
to be due in large part to the flavoring materials derived from 
the hops. Malt liquors contain about 4-10% of alcohol. 
The process of fermentation may be observed readily by 
adding yeast to water sweetened with molasses and keeping 
the mixture for some hours in a warm place. Bubbles of 
carbon dioxid are given off abundantly and a faint smell of 
alcohol may be detected. If some of the fermenting mixture 
be boiled in a flask to kill the yeast, the neck of the flask being 
plugged with a wad of cotton wool (which will permit the 
