32 BULLETIN 1187, U. S. DEPARTMENT OF AGRICULTURE. 
usually show a high percentage of acidity. It is understood of course 
that a low-grade flour, even when sound, will have a relatively high 
acidity, due to its inherent nature. 
The ash determination is more generally employed for detecting 
the relative grade of wheat flour. Usually the higher the grade of 
flour from a given wheat, the lower is the percentage of ash, indicat- 
ing that a less amount of the outer portion of the wheat kernel is in 
the flour. It should be borne in mind, however, that a low percent- 
age of ash is not an absolute indicator of high quality, as the soft 
wheats, as a class, which are relatively weaker on the average than 
the hard wheats, have low ash content. It should also be pointed 
out that flours milled from durum wheats run high in ash content, 
and that this does not preclude their making a fair loaf of bread. 
Considering individual samples, the total ash content appears to be 
in no way a distinguishing characteristic of flour made from different 
varieties of wheats or from wheats of different classes. 
The ash content of flour is always less than that of the wheat from 
which it is milled. In the product of the commercial mill there is 
less ash in the patent than in the lower grades. In milling for 
straight flour the ash content depends to some extent upon the close- 
ness of grinding. 
The gasoline color test of flour (p. 43) is of especial interest when 
made upon flours milled from durum wheats. This is doubly true 
when the test is interpreted in conjunction with the total protein and 
ash content of the flours. Durum wheats, with their relatively high 
protein content, generally speaking, lend themselves in a large 
measure to the manufacture of macaroni. The usual baking test 
with flour from this class of wheat gives good evidence as to the 
quality of gluten in the flour, and an ash determination indicates 
the grade of flour. The color of durum flours, cream to creamy 
yellow, is decidedly below the usual standard for bread-making 
purposes. On the other hand, from a macaroni standpoint the high 
color, so detrimental from a breadmaking standpoint, is just what is 
desired, and it is quickly and decisively brought to light by making 
a gasoline color test. 
Correct moisture determinations are of great importance, inas- 
much as under the pure food and drugs act no flour can carry more 
than 13.5 per cent moisture. Water in excess of this figure is con- 
sidered an adulteration. In making moisture determinations on 
whole grains for the purpose of grading or in connection with the 
tempering of wheat for milling, the Brown -Duvel moisture tester is 
usecl. 8 In making moisture determinations on ground material or 
flour the electric oven is used for a period of four to five hours at a 
temperature of 108° C. 
DESCRIPTION OF METHODS OF CHEMICAL DETERMINATIONS. 
The methods for making chemical determinations hereafter 
described are substantially those of the Association of Official Agri- 
cultural Chemists. Where modifications of these methods are 
described, it is believed that they do not vitiate the accuracy of the 
determination. They have been used by reason of their greater 
simplicity, ease of manipulation or lessening the time element in 
8 United States Department of Agriculture Handbook of Official Grain Standards, p. 34, 1922. 
