Properties Affecting the Commercial Value of Flour.
—Aside from its nutritive properties wheat flour has a commercial value depending upon its color and texture and upon the gluten which it contains. The character of gluten also varies largely in different varieties of wheat and in wheat grown in different localities. A chemical examination will not always tell the bread making properties of a flour, and the character of the bread itself depends often quite as much upon the skill of the baker as upon the flour which is used.
In cases where loaves are sold by weight, a flour with a high percentage of tenacious gluten is often preferred, since it permits of the forming of loaves containing a maximum percentage of water. With a flour rich in gluten it is not difficult to make a palatable loaf which does not bear any evidence of an excess of water, containing as much as 40 percent of moisture. The baking of bread is an art which is most successfully practiced by professionals, and the American method of home bread making does not always lead to the happiest results.
The ideal flour for bread making is one which contains a sufficient quantity of gluten to make a porous and spongy loaf, but not one which permits an excessive quantity of moisture to be incorporated in the loaf itself.
Average Composition of Different Varieties of Flour.
—Analyses of a great number of samples of different varieties of flours lead to the following data, which may be accepted as a very close approximation of the average variety of different grades of flour offered upon the American market:
| Name of Flour. | Mois- ture. | Pro- teids N × 6.25. | Pro- teids N × 5.70. | Moist Gluten. | Dry Gluten. | Oil. | Ash. | Starch N × 6.25. [26] | Starch N × 5.70. [26] | Crude Fiber. | Calo- ries. |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Perct. | Perct. | Perct. | Perct. | Perct. | Perct. | Perct. | Perct. | Perct. | Perct. | ||
| Patent flour, | 12.77 | 10.55 | 9.62 | 25.97 | 9.99 | 1.02 | 0.44 | 74.76 | 76.14 | 0.21 | 3,858.0 |
| Bakers’ and family flour, | 11.69 | 12.28 | 11.20 | 34.70 | 13.07 | 1.30 | 0.57 | 73.87 | 74.98 | 0.22 | 3,929.6 |
| Common market flour, | 12.28 | 10.18 | 9.28 | 24.55 | 9.21 | 1.30 | 0.61 | 75.63 | 76.53 | 0.28 | 3,882.5 |
| Miscellaneous flour, | 12.73 | 10.45 | 9.52 | 26.80 | 10.22 | 1.08 | 0.49 | 75.23 | 76.15 | 0.25 | 3,846.3 |
| Self-raising flour, | 11.45 | 9.75 | 8.89 | 26.97 | 9.65 | 0.70 | 4.45 | 73.66 | 74.51 | 0.21 | 3,719.3 |
| Gluten flour, | 12.99 | 13.30 | 12.13 | 39.68 | 14.84 | 1.05 | 0.55 | 72.11 | 73.28 | 0.32 | 3,891.1 |
[26] In the first of these columns the starch is calculated by difference, assuming the protein to be the quantity of nitrogen present multiplied by 6.25, and in the second column the figure is obtained in the same way, using 5.70 as the protein factor.
Separation of Gluten.
—The character of a wheat flour, as has already been intimated, is measured largely by the quantity of gluten which it may contain. The separation of gluten may be accomplished by any one, even without a chemical training, by a little practice. It is, therefore, one of the tests for the value of a wheat flour which can be easily and generally applied. The principle of separation of the gluten rests upon the fact that when wheat flour is moistened and kneaded into a sticky mass it may be washed with pure water with constant kneading until nearly all the starch has been removed from the mass. Meanwhile only that portion of the protein is removed which is soluble in the water and the gluten which is formed by the process of kneading remains as a sticky mass. When this moist mass is kneaded and rolled until all the moisture is taken out of it that can be removed in this way, it may be weighed and the proportion of moist gluten in the sample determined. It may then be placed in an oven and dried, and then the proportion of dry gluten secured. The following method is one which is easily applied. Place 10 grams of the sample in a porcelain dish and moisten with from 6 to 7 cubic centimeters of water, knead, and allow to stand for an hour. Work into a ball, being careful that none of the material adheres to the dish. Holding the mass in the hand knead it in a slow stream of cold water until the starch and all soluble matter are washed out. Place the ball of gluten thus formed in cold water and allow to stand for one hour; remove from water, press as dry as possible between the hands, roll into a ball, and weigh in a flat-bottomed dish. After weighing, place the ball of moist gluten in the drying oven for twenty hours; cool and weigh.