le of diet made from flour to
which the term bread is applied, and there are various ways of producing
the spongiform texture by which it is characterized. The ordinary and
doubtless the most satisfactory way is by developing the carbon dioxide
within the dough itself by the use of yeast (q.v.) or leaven, which sets
up alcoholic fermentation, splitting up the saccharine matters in the
flour into alcohol and carbon dioxide. The latter is retained by the
dough and distends it, causing the bread to "rise." Or the carbon
dioxide may be artificially introduced, as in the so-called "aerated"
bread (see below), or it may be produced by the agency of certain
chemicals, as for instance of baking powders.

Baking powders.

Such powders are mixtures which, under the influence of either water or
heat, evolve carbon dioxide. These powders have been divided by Jago
into three groups:--(1) _Tartrate_ powders, in which the acid
constituent is either free or partly combined tartaric acid; (2)
_Phosphate_ powders, in which the acid is some form of phosphoric acid;
(3) _Alum_ powders. All these powders have a more or less aperient
action on the human system. Tartrate powders have the disadvantage that
both commercial tartaric acid and cream of tartar frequently contain
lead, a poisonous substance. Phosphate powders are less open to
objection, as they are more easy to obtain free from lead and other
metallic impurities. Alum powders contain potassium bisulphate and alum.
It is somewhat remarkable that while the presence of alum in bread is
regarded by the law of England as adulteration, its use in baking powder
was pronounced legal in _James_ v. _Jones_, 1894, 1, Q.B. 304, on the
ground that baking powder is not food within the meaning of the Sale of
Food and Drugs Act 1875. In making wholemeal bread, hydrochloric acid
and sodium bicarbonate are often used in such proportions that they
neutralize each other. Carbon dioxide is evolved and raises the dough.
In preparing wholemeal bread the use of this combination has the
advantage that the acid acting rapidly on the sodium bicarbonate soon
produces enough carbon dioxide to aerate the dough, and thus hasten its
entry into the oven. Wholemeal flour contains so large a proportion of
cerealin that diastasis is apt to proceed rapidly, the result being a
clammy, sodden loaf. For this reason, perhaps the so-called aerated
process is even more suitable for making wholemeal than white bread.