370 BOARD OF AGEICULTURE. 



Bread is called unleavened when the flour is mixed with 

 water, thoroughly kneaded and baked at a high temperature ; 

 of which corn bread is a sample, and, from wheat flour, bis- 

 cuit, and hard-tack or sea-biscuit. Leavened bread is raised 

 bread, — a moist, light, porous, spongy substance, easy to 

 masticate and digest. A little butter or lard and salt (with 

 sugar, if desired) is carefully mixed with the flour, and either 

 milk or water, — lukewarm, — with yeast, is added, and 

 made, by careful stirring, into a paste or dough, which is ex- 

 posed to a temperature of from 50° to 80° until fermentation 

 is fully established. Carbonic acid gas and alcohol is gen- 

 erated ; the gas is absorbed or retained by the gluten, causing 

 the dough to swell up into an elastic, spongy mass, when it 

 is thoroughly kneaded with more flour, made into loaves and 

 put in a warm place until fermentation is again actively es- 

 tablished, Avhen it is placed in an oven heated to a tempera- 

 ture of from 350° to 500°, where it remains until cooked. 



The alcohol and some gaseous products are driven oft' by 

 the high heat of the oven. The gluten and starch v/hich is 

 partially soluble is mixed with the fluids, which surround 

 the particles with a thin film of moisture. The fine, invisi- 

 ble bubbles of carbonic acid gas generated in every part of 

 the loaf overcome the adhesiveness of the gluten, and sepa- 

 rate the myriads of particles from each other. The high 

 temperature converts the moisture into steam, ruptures the 

 starch granules, softens and renders the starch and gluten 

 soluble and well prepared for the free action of the digestive 

 ferments. Other interesting changes occur in the cooking 

 of bread. Wheat, in common with all cereal grains, contains 

 a ferment called diastase, which is chiefly found in the corti- 

 cal part, but is diffused through all parts of the seed. Aided 

 by warmth and moisture, this agent is the active principle in 

 the process of germination. The seed, buried in the moist 

 earth and warmed by the sun, absorbs water. The germinal 

 cells are quickened from dormant into active life. The 

 diastase changes the starch into dextrine and grape sugar, 

 the food of the germinal cells ; the tiny leaf shoots upward 

 to the sunlight, the rootlets strike into the earth, and when 

 the stored starch of the seed is consumed the plant can de- 

 rive its nutriment from earth and air. 



