WHEAT Wheat as Raw Material.—The embryo or germ from which the new plant originates forms from i% to 2% of the wheat berry. The endosperm is the food upon which the young plant lives till it is able to obtain its sustenance from the soil and air. The endosperm in its original form cannot, however, be assimi lated by the embryo, and certain enzymes in the presence of moisture gradually bring about the necessary changes. As a consequence the endosperm becomes liquid, and the bran func tions as a container to it. This bran is very resistant to disin tegration and can be found in the soil as an empty sac weeks or months after sowing.
The miller essentially divides wheat into two products, flour and offal, though there are several grades of each. The embryo or germ is sometimes regarded as a third product, but actually it goes into the two named. Until modern methods of milling were invented it was never obtained as a separate product, and even to-day it is impossible to separate more than about of the whole, that is to say, more than about a of the 2% contained in the wheat berry. Germ, because of its oily nature, is particularly resistant to disintegration. Pressure applied either by millstones or rolls may flatten the particles and express some of its oil from the germ into the flour; but it is an error to suppose that flours manufactured by millstones contained the germ, and that those manufactured by modern methods do not. Formerly the germ went mainly or wholly into the by-products; to-day some of it is extracted as substantially a separate product and is added, after cooking (which is necessary), to white flour to form certain special flours, e.g., Hovis, a well known English product. The remainder goes mainly or wholly into the by-products of milling. Flours containing raw germ will not remain sound under trying conditions for a considerable period. The enzymes provided by nature to convert the endosperm into plant food reside mostly in or near the embryo or germ, and their activities have to be con trolled or nullified in preparing the germ for use in bread ; but ways have been devised whereby to some extent it can be included in certain flours.
The miller divides the berry essentially into two products, flour and branny husk. The bran is made up of several layers. For present purposes it is unnecessary to deal with other than two of them. The outer skin (epidermis) is, to some extent, sepa rated from the inner layers during the processes of milling, and is the principal constituent of the material known to millers as "bee's wing," a name indicative of its appearance. This bee's wing has a very high fibre content and is of low or little food value.
On the inner side of the bran there is a layer of rectangular cells known as the aleurone cells, of higher nutritive value than the bran. Theoretically wheat should yield much more flour than millers usually extract. Hence, if any attempt were made in commerce to increase the extraction, it is the inner side of the branny husk which should be attacked, not the outer one. When wheat was passed between millstones, it was principally the epi dermis which was removed and passed as bran powder into the flour; the aleurone cells were left then, as they are now, on the finished bran. The addition of such powdered material to flour darkened it and had some effect in lowering its food value.
All wheats, moreover, have a crease. This greatly impedes an easy and satisfactory separation of wheat into its component com mercial parts. It is also a receptacle for dust and dirt. In the early days of modern milling, millers attempted to split each berry down the crease and obtained a very dark product known as crease flour or crease dirt. This attempt proved to be a failure. A pair of fluted rolls, 6o in. long, grinds as a normal feed about 50,000,000 berries of wheat per hour, and it proved impossible to split each berry, or even most of them, in the desired way. Instead, wheat washing was introduced. The berry, furthermore, is furnished at one end with "hairs of beard" (which must not be confounded with the awns attached to the glumes), and these hairs have also to be removed by the miller.
The proportions of cellulose and ash present in flour are largely under the control of the miller. The cellulose is sometimes de scribed as woody fibre, and by excluding particles of branny husk the proportion present of this indigestible matter is low. The ash consists principally of phosphates of potash and to a much smaller extent of phosphates of magnesia and lime, with traces of other constituents. The proportion of ash may be as low as 0.35% in the highest grades of flour or may rise to, say, i% in the com mercially lowest grades. In no case is the presence of calcium salts of substantial significance, and this applies to wheatmeals also. The form in which these constituents are combined in wheat has not been definitely ascertained, but if such salts may be di vided into two groups, organic and inorganic, they are at that stage mainly or wholly organic, but become largely inorganic as a result of inorganic action during the milling and bread making processes.