29. As has already been explained, yeast, in order to grow, requires
something on which to feed, and the food that produces the most rapid
growth is that which contains carbohydrate. Certain of the
carbohydrates, however, prove to be better food and produce more rapid
growth than others, and these, which are known as yeast aids, are
usually added as ingredients in the making of bread. The ones that are
most commonly used are sugar and potato water. Sugar is almost always
added, but it should be limited in quantity, because a dough mixture
that is made heavy with sugar will rise very slowly. Potato water has
been found to be a very satisfactory aid, because the starch of the
potato is utilized readily by the yeast. If this aid is to be used, the
water in which potatoes are boiled may be saved and, when the
ingredients required for the making of bread are mixed, it may be added
as a part or all of the liquid required. If it is desired to increase
the amount of starch in the potato water, a boiled potato or two may be
mashed and added to it.