In the process of bread-making, the gluten undergoes fermentation by the action of the leaven and liberates carbonic acid, which causes the dough to become porous and swell up, or, as it is termed, to rise. Bread contains the same substances as flour, but gluten and starch are present in a state that does not admit of their separation by mechanical means, and glucose, if present at all, exists in a smaller quantity: the proportion of dextrine and water is, on the other hand, considerably increased. The bread of the Paris city bakeries contains 40 per cent. of water—the crumb, which forms 5/6 of the weight of the bread, containing 45 per cent.; the crust, which constitutes the remaining 1/6, containing 15 per cent. In army bread 43 per cent. of water are contained—the crumb, which constitutes 4/5 of the weight of the bread, holding 50 per cent.; the crust which forms the remaining 1/5, containing 15 per cent.
The addition of common salt naturally increases the proportion of ash left upon calcining bread.
Water is contained in stale bread in the same quantity as in fresh bread; but exists in a modified molecular condition: upon heating stale bread, it acquires the properties of fresh bread.
The following substances are used in the adulteration of wheaten flour:[P]
- Potato-starch.
- Meals of various grains (rice, barley, corn, oats and rye).
- Vegetable meals, (beans, horse-beans, kidney-beans, peas, vetch, lentils, etc.).
- Darnel meal.
- Buckwheat flour.
- Linseed-meal.
- Mineral substances (plaster, chalk, lime, alum, and sulphate of copper).
In order to detect these substances, the gluten, the starch, and the ash are separately examined.
a. EXAMINATION OF THE GLUTEN.
In order to separate the gluten, two parts of the flour to be examined and one part of water are mixed into a paste, and this is placed in a fine linen sack, in which it is kneaded under a stream of water so long as the washings have a turbid appearance: these are preserved. The gluten obtained from good wheaten flour possesses a light-yellow color; emits a stale odor; and spreads out, when placed in a saucer. In case the flour has been too strongly heated in the grinding, or otherwise badly prepared, the gluten is granulous, difficult to collect in the hand, and somewhat resembles flint-stone in appearance.
Gluten prepared from a mixture of equal parts of wheat and rye is adhesive, blackish, without homogeneousness, spreads out more readily than pure wheaten gluten, separates easily and adheres somewhat to the fingers.
Gluten obtained from a mixture of wheat and barley is non-adhesive, of a dirty reddish-brown color, and appears to be formed of intertwined vermicular filaments.