5i8 THE POPULAR SCIENCE MONTHLY. 



chief cause of the chippy character of aerated bread. It must be re- 

 membered that this stage is protracted over several hours, during 

 which the temperature most favorable to germination is steadily main- 

 tained. 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 common- 

 ly, 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 boil- 

 ing, 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 sup- 

 pose. 



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 w^ater, 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 improv- 

 ing 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 2f?. 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 



