Page:Popular Science Monthly Volume 25.djvu/532

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THE POPULAR SCIENCE MONTHLY.

chief cause of the chippy character of aërated bread. It must be remembered that this stage is protracted over several hours, during which the temperature most favorable to germination is steadily maintained. Other and very interesting phenomena connected with bread-making will be treated in my next.

 
XXXIII.

The practical importance of the fermentation described in my last is strikingly shown by the fact that, in the course of sponge-rising, dough-rising, and baking, a loaf becomes about four times as large as the original mixture of flour, water, etc., of which it was made; or, otherwise stated, an ordinary loaf is made up of one part of solid bread to more than three parts of air-bubbles or pores. French rolls, and some other kinds of fancy bread, are still more gaseous.

So far I have only named the flour, water, salt, and yeast. These, with a little sugar or milk added according to taste and custom, are the ingredients of home-made bread, but "baker's bread" is commonly, though not necessarily, somewhat more complex. There is the material technically known as "fruit," and another which bears the equivocal name of "stuff," or "rocky." The fruit are potatoes. The quantity of these prescribed in Knight's "Guide to Trade" is one peck to the sack of flour. This proportion is so small (about three per cent by weight) that, if not exceeded, it can not be regarded as a fraudulent adulteration, for the additional cost involved in the boiling, skinning, and general preparing of the small addition exceeds the saving in the price of raw material. The fruit, therefore, is not added merely because it is cheaper than flour, as many people suppose.

The instructions concerning its use given in the work above named clearly indicate that the potato-flour is used to assist fermentation. These instructions prescibe that the peck of potatoes shall be boiled in their skins, mashed in the "seasoning-tub," then mixed with two or three quarts of water, the same quantity of patent yeast, and three or four pounds of flour. The mixture is left to stand for six or twelve hours, when it will have become what is called a ferment. After straining through a sieve, to separate the skins of the fruit, it is mixed with the sack of flour, water, etc.

It is evident from this that it would not pay to add such a quantity in such a manner as a mere adulterant. The baker uses it for improving the bread, from his point of view.

The stuff or rocky consists, according to Tomlinson, of one part of alum to three parts of common salt. The same authority tells us that the bakers buy this at 2d. per packet, containing one pound in each, and that they believe it to be ground alum. They buy it thus for immediate use, being subject to a heavy fine if they keep alum on the premises. The quantity of the mixture ordinarily used is eight ounces