MECHANICAL AND USEFUL ARTS. 



113 



The speaker stated that the principal object he had in view in 

 delivering the discourse was to answer the question so often put as 

 to what was "Aerated Bread." Bread, as used at table, assumed two 

 forms dependent on its preparation, vcsiculated and unvcsiculated. 

 The latter is known under the name of unleavened bread, and con- 

 sists of such preparations of flour as biscuits, passover cakes, &c. 

 Vesiculated bread is prepared in two ways, either by fermentation or 

 aeration. In all case3 fermented bread is made from the flour of wheat, 

 or a mixture of this with the meal or flour of other grain. Barley, oats, 

 maize, rj - e, will not alone make fermented bread. The meal of these 

 grains is added to wheaten flour when they are made into bread. 



AVheaten flour is made from the grains of wheat, which are the 

 fruit of the plant. Six layers of cellular tissue were described be- 

 tween the albumen or perisperm of the seed and the outside of the 

 grain: — 1, the epicarp ; 2, the sarcocarp ; 3, the endocarp (these 

 belong to the fruit) ; 4, the testa of the seed ; 5, a secondary mem- 

 brane ; 6, the covering of the perisperm. These layers constitute 

 the bran, which is separated from the fine flour. They contain the 

 same chemical constituents as the flour, and so far from being objec- 

 tionable, are a desirable addition to the flour. The gluten of the 

 flour is represented in the bran by a principle, called by its dis- 

 coverer cerealin. Like gluten it acts as a ferment, but its power in 

 this respect is said to be destroyed at a temperature of 150° Fahr. 

 It is soluble in cold water, and in that state acts as a ferment. Bran 

 tea accelerates the changes of fermentation. It is this agent which, 

 during the fermentation of bread, gives the brown colour to meal 

 bread. Twenty-one ounces of wheat yield five ounces of bread, and 

 sixteen ounces of fine flour. One pound of flour contains — 



The gluten and albumen are flesh-forming substances, sugar and 

 starch heat-giving. In the making of fermented bread yeast is added 

 to the flour, and the gluten is put into a state of change, but not de- 

 composed. Asmall portion of the starch is converted into glucose, which 

 is decomposed, and alcohol formed, and carbonic acid produced. The 

 carbonic acid gas escaping from the mass vesiculates the bread. The 

 quantity of starch changed in this process is very small. It is ex- 

 pressed by the quantity of carbonic acid gas necessary for the vesicula- 

 tion of the bread, as little or none of this gas escapes in the rising of 

 the bread. The conversion of starch into glucose during the fermenta- 

 tion of the bread does not appear to be greater than is necessary to 

 form the carbonic acid for vesiculation. The starch during fermenta- 

 tion acquires the power of being more quickly converted into glucose 

 and its subsequent products than when heated and not exposed to 

 this process. This is probably thegreat peculiarity of fermented bread, 

 that the starch more rapidly passes into a state of change. 



When the starch of wheat has already acquired this tendency to 



