Enveloping the entire kernel is a husk, or bran
covering, _h_. This forms a protection to the rest of the grain, but it
cannot be used as food, because it is composed almost entirely of
cellulose, which is practically indigestible. The center of the grain,
or the heart, is the softest part and consists of cells filled with
starch. From this soft center the contents of the grain gradually grow
harder toward the outside, the harder part and that containing the most
gluten occurring next to the bran covering.
13. MILLING OF WHEAT FLOUR.--Great advances have been made in the
production of flour from wheat, and these are very good evidence of
man's progress in the way of invention. The earliest method consisted
in crushing the grain by hand between two stones, and from this crude
device came the mortar and pestle. A little later millstones in the form
of thick, heavy disks were brought into use for grinding grain. Two of
these stones were placed so that their surfaces came together, the lower
one being stationary and the upper one made to revolve. Early grinding
apparatus of this kind was turned by human power, but this kind of power
was first displaced by domestic animals and later by wind and water. Out
of this arrangement, which is still used to some extent in small mills,
has grown the present-day complicated machinery of the roller process,
by which any part of the grain may be included or rejected.
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