THE CHEMISTRY OF THE KITCHEN. 371 



In the process of rising and baking of bread, the moisture 

 and heat enable the diastase of the flour to convert a part of 

 the starch into dextrine and sugar. The sugar, by the fer- 

 mentation, is converted into alcohol and carbonic acid. 

 When the temperature of the bread reaches 140° the yeast 

 cells cease to act, and the high temperature of the oven con- 

 verts the surface of the loaf into a dense crust, which pre-^ 

 vents it from shrinking when the formation of the gas is 

 checked, and this is long before the cooking is completed. 

 The starch on the surface is changed by the high heat into 

 dextrine and caramel, and is richer in nutriment and more 

 easy to digest than the white part of the loaf. 



Other materials beside yeast are used to generate carbonic 

 acid gas in the cookery of flour, — such as bicarbonate of soda 

 and potassa, carbonate of ammonia, reacting upon the lactic 

 acid of sour milk, hydrochloric acid, tartaric acid, bitartrate 

 of potassa and the acid phosphate of lime. The baking 

 powders in the market are made from these chemicals. 

 They are quick in their action and convenient for the house- 

 keeper, but the yeast process makes the nicest bread. The 

 cereals may be cooked by baking, steaming, boiling and 

 frying. Oats, barley, rice and corn have no gluten and can- 

 not be made into raised bread. Rye has gluten and can be 

 raised in cooking. Other forms of starch foods are sago, 

 tapioca, arrowi'oot, corn starch, and the familiar potato. 



We must pay our respects to our friend, the potato. 

 There are many varieties of this tuber, difiering chiefly in 

 color, form and the percentage of sugar and starch they con- 

 tain. 



A potato uncooked is a hard, disagreeable customer for 

 the palate. The substance of the potato is made up of cellu^ 

 lar tissue, penetrated and surrounded by a watery, albumi- 

 nous juice, and filled with starch granules. The object of 

 cookino; is the rupture and softenino; of the starch granules 

 and the albuminous cellular tissues. When well done, we 

 have a changed potato, soft, floury, mealy, inviting to the 

 eye, acceptable to the palate, and, next to the cereals, the 

 most valuable of all our vegetable foods. They may be 

 baked, boiled, steamed or fried. Except when fried, they 

 should be cooked in their "jackets," to retain their potash 



