There are several methods of converting wheat into flour. One is by grinding between two horizontal stones, the upper one revolving, and the lower one stationary. The surface of the stones presents an infinite number of minute cutting edges. The upper stone is convex, the lower one concave; but instead of fitting perfectly, they approach closer together from the centre outward, so that, as the grain is poured into an opening in the upper stone, it is at first rather coarsely crushed, and then cut finer and finer, as it is carried to the circumference by the centrifugal force. As the grain leaves the stones, the outer husk has been least affected; the tough, coherent gluten is divided minutely, while the brittle starch, which forms two thirds of the grain, is completely crushed. The miller then divides these products, by sifting or bolting, into fine flour, coarse flour; and bran.
The bran should be discarded as utterly useless for human food; but it is often mixed with an inferior quality of fine flour, and sold as Graham flour. It was at one time considered valuable as a food for those suffering from constipation, chiefly on account of its coarseness; but science has shown us recently that minute points of glass (and bran is nothing else) are not Nature's best agents in removing effete matters from the system. All of the so-called Graham flour made by this process should be sifted before using.
The coarse flour will vary in quality, according as it has more or less of the outer bran mixed with it. In the soft wheats the husk peels off readily under the stones, and is easily separated by bolting; and as these soft varieties contain the smallest proportion of gluten, they yield a coarse flour, containing only an average amount of gluten, and the whitest fine-flour. But in the hard, flinty wheats, this outer husk clings so closely that much of it is ground up finely with the flour, giving it a dark color. This flour, as it contains a large proportion of gluten, would be more nutritious were it not that much of the gluten adheres to the hulls, and is lost by sifting them out, and much of the fine, flinty bran is retained in the flour, which makes it irritating and indigestible.
The quality of the fine flour depends upon the quality of the wheat, in the first place; also upon the number of sift-ings, being richer in gluten the less it is sifted; and upon the way in which it is stored. The process of grinding with the stones heats the flour; and as it is often thrust upon the market without being properly cooled and dried, it spoils very rapidly. Flour made by this process of grinding is called the St. Louis, or old-process flour. When made of the very best quality of grain and carefully prepared, it makes a sweet, nutritious bread, and is excellent in cake and pastry. It is often designated pastry flour.
Another method of making flour is by the new, or Haxall process, so called from the name of the inventor. By this process the outer husk is first removed, or decorticated; then the cleaned grain is cut by a system of knives, which reduces it to a fine powder without the injurious effects of heating. This flour has a slightly granular consistency, owing to the presence of minute particles of hard. flinty gluten. It is usually made from the best quality of wheat, and keeps well. It is considered by many as the best flour for bread, as it makes a whiter, nicer-looking loaf. Haxall flour swells more than that made by the old process, as it contains more of the gluten; the same measure making a greater quantity of bread than the St. Louis flour. It is, therefore, cheaper in the end, though costing more per barrel. By repeated sittings, this flour loses its gluten, as does that made by the St. Louis process, and consequently is then inferior as a food. But we can supply by other flours and other food what this flour lacks in nutritious qualities; and until the popular taste is educated to demand the amount of nutriment contained in bread rather than the whiteness of it, as a test of its quality, it is well to make our fine, white bread from this, which is the best flour, and have it as nearly perfect as possible.
There have been many variations of the Haxall process, and all are included under the term new-process flour.