Page:Popular Science Monthly Volume 25.djvu/534

520 packets of "stuff" or "rocky," or any other bleaching abomination.

Liebig asserts that in certain cases the use of lime-water improves the quality of bread. Tomlinson says that, "in the time of bad harvests, when the wheat is damaged, the flour may be considerably improved, without any injurious result whatever, by the addition of from twenty to forty grains of carbonate of magnesia to every pound of flour." It is also stated that chalk has been used for the same purpose. These would all act in nearly the same manner by neutralizing any acid that might already exist or be generated in the course of fermentation.

When gluten is kept in a moist state it slowly loses its soft, elastic, and insoluble condition; if kept in water for a few days, it gradually runs down into a turbid, slimy solution, which does not form dough when mixed with starch. The gluten of imperfectly ripened wheat, or of flour or wheat that has been badly kept in the midst of humid surroundings, appears to have fallen partially into this condition, the gluten being an actively hygroscopic substance.

Liebig's experiments show that flour in which the gluten has undergone this partial change may have its original qualities restored by mixing one hundred parts of flour with twenty-six or twenty-seven parts of saturated lime-water and a sufficiency of ordinary water to work it into dough. I suspect that the action of the alum is of a similar kind, though this does not satisfactorily account for the bleaching.

The action of sulphate of copper, which has been used in Belgium and other places for improving the appearance and sponginess of loaves, is still more mysterious than that of alum. Kuhlmann found that a single grain in a four-pound loaf produced a marked alteration in the appearance of the bread. Fortunately, this adulteration, if perpetrated to a mischievous extent, may be easily detected by acidulating the crumb, and then moistening with a solution of ferrocyanide of potassium. The brown color thus produced betrays the presence of copper. The detection of alum is difficult.

I should add that the ancient method of effecting the fermentation of bread, and which I understand is still employed to some extent in France, differs somewhat from the ordinary modern practice described in my last. When flour made into dough is kept for some time moderately warm, it undergoes spontaneous fermentation, formerly described as "panary fermentation," and supposed to be of a different nature from the fermentation which produces yeast.

Dough in this condition is called leaven, and when kneaded with fresh flour and water its fermentation is communicated to the whole lump; hence the ancient metaphors. In practice the leaven was obtained by setting aside some of the dough of a previous batch, and adding this when its fermentation reached its maximum activity. One