FLOUR 57
in each hand alternately, the hand being dried meanwhile on a towel ; when
no more moisture is given up to the hand, the gluten is weighed on a clock-
glass.
The external characters (colour, odour, elasticity and tenacity) of the
gluten indicate its quality and so the behaviour of the flour as regards
bread-making.
Special apparatus may be used by means of which the swelling power of
the gluten on heating is determined, but the indications thus obtained are In
no way more valuable than those of a qualitative study of the external characters.
(b) DRY STATE. The dry gluten may be calculated approximately
from the percentage of moist gluten by dividing by three. A more exact
direct determination may be made as follows:
The gluten obtained as in (a) is dried on a nickel plate in an air-oven at
105° to constant weight, this requiring about 20 hours. A more rapid
procedure consists in flattening the gluten out on the nickel plate by means
of the finger and drying at 120° for 2-5-3-5 hours. The weight is referred
to 100 parts of flour.1
With practice this method gives concordant results. As regards the extrac-
tion of the gluten, this is easy with fine wheat flour and ordinary bread flour,
but difficult with inferior flours, and the latter may conveniently be manipulated
under the water in a thin linen bag. Flours of other cereals do not yield gluten
when treated in this way.
8. Acidity.—5 grams of the flour and 25 c.c. of 90% alcohol, neu-
tralised exactly with N/20-caustic soda solution, are shaken at intervals
during a day in a cylinder with a ground stopper. After standing over-
night, 10 c.c. of the clear liquid are titrated with N/20-caustic soda in
presence of phenolphthalein or tincture of turmeric.2 *
The acidity is expressed as either sulphuric or lactic acid : I c.c. N/zo-
soda = 0-00245Jgram H2S04 or 0-0045 gram C3H603. It may also be
expressed simply as the number of c.c. of normal soda required per 100
grams of flour, this being termed the degree oj acidity.
The acidity, ash, external characters, colour and gluten furnish the best
data for valuing flour.
Besides by the above method, the acidity is determined also by other methods,
sometimes alcohol and sometimes water being used as solvent; the alcohol
methods are to be preferred. Results are comparable only when obtained by
the same method, which should always Jbe indicated,
9. Detection of Alterations.—When badly stored, especially in moist
surroundings, wheat flour undergoes change with development of a dfs~
agreeable odour and sharp taste in consequence of attack by various moulds*
Certain changes arise from diseases of the grain such as smut (Ustilago carbo),
rust (Uredo linearis), bunt (Tilletia caries), etc. The presence of the moulds
or spores is detected to some extent by the physical examination and Is
rendered certain, by microscopical examination.
1 Neumann and Salecker : Zeitschr. UnL Nahr- u. Genuss-mittel, 1908, I, p. 735*
a Tincture of turmeric is prepared by macerating i part of powdered, turmeric
root with, ro parts of 60% alcohol for some days and filtering the alcoholic extract*
It is best to follow the procedure indicated in the chapter on fiesh foods (p. 8, note).