If crude gluten, obtained as above, is subjected to the action of hot alcohol, it is separated into two distinct substances, one soluble and the other insoluble. As the solution cools, a further separation takes place of a substance soluble in hot alcohol but not in cold, and another soluble in either hot or cold alcohol. The first, viz. that insoluble in either hot or cold alcohol, has been named gluten-fibrin; that soluble in hot alcohol, but not in cold, gluten-casein; and that soluble in either hot or cold alcohol, glutin. I give these names and explain them, as my readers may be otherwise puzzled by meeting them in books where they are used without explanation, especially as there is another substance presently to be described, to which the name of ‘vegetable casein’ has also been applied. The gluten-fibrin is supposed to correspond with blood-fibrin, gluten-casein with animal-casein, and glutin with albumen. Their composition is as follows, which I append for what it is worth in connection with this theory, but mainly to show how small is the difference between the chemical composition of the nitrogenous constituents of animals and those of plants. I shall come to this subject again:
| — | Gluten-Fibrin | Gluten-Casein | Glutin |
| Carbon | 53·23 | 53·46 | 53·27 |
| Hydrogen | 7·01 | 7·13 | 7·17 |
| Nitrogen | 16·41 | 16·04 | 15·94 |
| Oxygen and sulphur | 23·35 | 23·37 | 23·62 |
| — | Blood-Fibrin (Scherer) | Animal-Casein | Albumen |
| Carbon | 53·57 | 53·83 | 53·50 |
| Hydrogen | 6·90 | 7·15 | 7·00 |
| Nitrogen | 15·72 | 15·65 | 15·50 |
| Oxygen and sulphur | 22·81 | 23·37 | 24·00 |
Gluten is usually described as ‘partly soluble in hot water.’ My own examination of this substance suggests that ‘partially soluble’ is a better description than ‘partly soluble’ (Miller) or ‘very slightly soluble’ (Lehmann). This difference is not merely a verbal quibble, but very real and practical in reference to the rationale of its cookery. A partially soluble substance is one which is composed of soluble and also of insoluble constituents, which, as already stated, is strictly the case with gluten in reference to the solvent action of hot alcohol. A very slightly soluble substance is one that dissolves completely, but demands a very large quantity of the solvent. I find that the action of hot water on gluten, as applied in cookery, is to effect what may be described as a partial solution—that is, it effects a loosening of the bonds of solidity without going so far as to render it completely fluid.
It appears to be a sort of hydration similar to that which is effected by hot water on starch, but less decided.
To illustrate this, wash some flour in cold water so as to separate the gluten in the manner already described; then boil some flour as in making ordinary bill-stickers’ paste, and wash this in cold water. The gluten will come out with difficulty from this, and, when separated, will be softer and less tenacious than the cold-washed specimen. This difference remains until some of the water it contains is driven out, for which reason I regard it as hydrated, though I am not prepared to say that the hydration is of a truly chemical character—a definite chemical combination of gluten with water; it may be only a mechanical combination—a loosening of solidity by a molecular intermingling of water.
The importance of this in the cookery of grain-food is very great, as anybody who aspires to the honour of becoming a martyr to science may prove by simply making a meal on raw wheat, masticating the grains until reduced to small pills of gluten, and then swallowing them. Mild indigestion or acute spasms will follow, according to the quantity taken and the digestive energies of the experimenter. Raw flour will act similarly, but less decidedly.
Bread-making is the most important, as well as a typical example, of the cookery of grain-food. The grinding of the grain is the first process of such cookery; it vastly increases the area exposed to the subsequent actions.
The next stage is that of surrounding each grain of the flour with a thin film of water. This is done in making the dough by careful admixture of a modicum of water and kneading, in order to squeeze the water well between all the particles. The effect of insufficient enveloping in water is sometimes seen in a loaf containing a white powdery kernel of unmixed flour.
If nothing more than this were done, and such simple dough were baked, the starch granules would be duly broken up and hydrated, the gluten also hydrated, but, at the same time, the particles of flour would be so cemented together as to form a mass so hard and tough when baked, that no ordinary human teeth could crush it. Among all our modern triumphs of applied science, none can be named that is more refined and elegant than the old device by which this difficulty is overcome in the everyday business of making bread. Who invented it, and when, I do not know. Its discovery was certainly very far anterior to any knowledge of the chemical principles involved in its application, and probably accidental.
The problem has a very difficult aspect. Here are millions of particles, each of which has to be moistened on its surface, but each, when thus moistened, becomes remarkably adhesive, and therefore sticks fast to all its surrounding neighbours. We require, without altogether suppressing this adhesiveness, to interpose a barrier that shall sunder these millions of particles from each other so delicately as neither to separate them completely nor allow them to completely adhere.