Experimental cookery

The milling process and the structure o£ wheat. The wheat kernel may be divided into three main parts: the bran, the germ, and the endosperm, the relative proportion of each part of the entire kernel being respectively about 14.5, 1.5, and 84 per cent. Milling is the process of separation of the endosperm from the bran and germ. When no separation is made, or all the flour streams are reunited, the flour is known as whole- wheat flour, but otherwise the completeness of separation determines the resulting grade of flour. If the separation is so complete that only the heart of the endosperm is used, the resulting flour may be called a ''fancy" or ''short" patent. In general, only about 72 to 75 per cent of the endo- sperm is obtained in white flour, the remainder constituting bran and shorts. Between the two extremes of flour, whole-wheat and fancy patent, are many other varieties. The steps in the milling process may include the following: cleaning, tempering, breaking, sifting, or separating the primary products, purifying, reducing, bolting, flour blending, and bleaching. The structure of the wheat berry is shown in Fig. 42. Layer No. 1, some- times called the bee's wings by millers, the hairs, and the dirt on the berry, particularly that in the crease, are removed in the cleaning operations pre- paratory to milling. Layers No. 2 to No. 6, shown in the surface drawing, and the longitudinal and cross sections constitute the bran coats. The gross appearance of a cross section of a wheat berry varies some- what with the type of wheat and the ripening conditions. Hard wheats are more flinty and vitreous than soft wheats. The proportion of gluten is usually higher in hard than in soft wheats, and the gluten forms a con- tinuous matrix in which the starch granules are imbedded. When the grain contains a large proportion of gluten, the starch granules, as it dries out in 391 392 FLOUR AND BREAD Cmirtcsy of Intcntational Milling Company, Minneapolis Fig. 42. — The structure of a wheat kernel. The bran layers are shown peeled back from the kernel. The portion from which the different flours are obtained is shown in the longitudinal section. THE MILLING PROCESS 393 ripening, are more firmly cemented to or held in the gluten matrix. In milling the vitreous wheats naturally tend to yield coarser particles and less free starch granules than soft wheats, unless the hard wheats are deliber- ately ground fine. If the weather is hot and dry after flowering of the wheat, a larger proportion of gluten and less starch are laid down in the kernel. It is known that vitreous barley has smaller starch granules than soft barley, and it is probable that this also applies to wheat. In contrast to hard wheats, the soft wheats have air spaces throughout the endosperm. The endosperm is quite friable and naturally breaks into smaller particles in milling.