of a flour can
be accurately determined from the color, granulation, absorption, gluten
and ash content, and the quality of the bread. Technical flour testing
requires much experience and a high degree of skill.

168. Bleaching.--In the process of manufacture, flours are often
subjected to air containing traces of nitrogen peroxide gas, generated
by electrical action and resulting in the union of the oxygen and
nitrogen of the air. This whitens and improves the color of the flour.
Bleached flours differ neither in chemical composition nor in nutritive
value from unbleached flours, except that bleached flours contain a
small amount (about one part to one million parts of flour) of nitrite
reacting material, which is removed during the process of bread making.
The amount of nitrites produced in flour during bleaching is less than
is normally present in the saliva, or is found naturally in many
vegetable foods, or in smoked or cured meats, or in bread made from
unbleached flour and baked in a gas oven where nitrites are produced
from combustion of the gas. The bleaching of flour cannot be regarded as
in any way injurious to health or as adulteration, and a bleached flour
which has good gluten and bread-making qualities is entirely
satisfactory. It is not possible to successfully bleach low-grade flours
so they will resemble the high grades, because the bran impurities of
the low grades blacken during bleaching and become more prominent.
Alway, of the Nebraska Experiment Station, has shown that there is no
danger to apprehend from over-bleaching, for when excess of the
bleaching reagent is used, flours become yellow in color[65]. Similar
results have been obtained at the Minnesota Experiment Station. As
bleaching is not injurious to health, and as it is not possible through
bleaching to change low grades so as to resemble the patent grades,
bleaching resolves itself entirely into the question of what color of
flour the consumer desires. Pending the settlement of the status of
bleaching the practice has been largely discontinued.

[Illustration: FIG. 45.--WHEAT HAIRS AND DEBRIS IN LOW GRADE FLOURS.]

169. Adulteration of Flour.--Flour is not easily adulterated, as the
addition of any foreign material interferes with the expansion and
bread-making qualities and hence is readily detected. The mixing of
other cereals, as corn flour, with wheat flour has been attempted at
various times when wheat commanded a high price, but t