THE CHEMISTRY OF THE KITCHEN. 369 



per cent, of mineral matter in rice to 3 in corn. They are 

 all rich in starch, but they vary widely in nitrogenous, dex- 

 trine, fatty and mineral matter. Starch is therefore the 

 chief element aflected by the process of cooking. 



Starch is found in vegetable substances only. In grain it 

 consists of minute granules, made up of concentric layers, 

 insoluble at ordinary temperatures, and of no use as food 

 until converted into dextrine and grape sugar. By cooking, 

 the starch is prepared for the action of the digestive fer- 

 ments, the ptyalln and mucin of the saliva, and the trypsin 

 of the pancreatic secretion, by which this change is effected. 

 The residue not acted upon, digested by these ferments, 

 leaves the body in the feces.* 



Of the cereal grains used for food, wheat is the most val- 

 uable and most extensively cultivated. It is rarely con- 

 sumed whole, but is subjected to processes of milling and 

 grinding, and is furnished for use in the form of flour. Be- 

 sides sixty-six per cent, of starch, wheat flour contains, as a 

 part of its nitrogenous material, a substance, composed of 

 vegetable fibrine, mucine and glutine, called gluten, — about 

 eleven per cent. , — which gives to the moistened flour peculiar 

 tenacious adhesive qualities. These two bodies, starch and 

 gluten, undergo important changes in the chemistry of the 

 kitchen. The presence of both is necessary in the prepara- 

 tion of one of the most valuable and most highly prized of 

 all foods, — good bread. 



Yeast is an agent capable of exciting alcoholic fermenta- 

 tion in mixtures when exposed to air and warmth, contain- 

 ing starch, sugar and nitrogenous matter. It will act at a 

 temperature varying between 40° and 140°, but is most 

 active at a temperature between 60° and 100°. 



* It may be well in this connection to consider the action of a ferment. Ferments 

 are substances, either organized, like the cells of yeast, — when living and functional, 

 fermentation takes place ; when they die, it ceases, — or tlie ferment may be unorgan- 

 ized, a substance like the ptyalin of the saliva and other digestive ferments. Fer- 

 ments are known by their effects ; they have never been completely isolated. The 

 action of a ferment is not chemical ; it has no chemical reactions or combinations, 

 and is not consumed by its action, but will continue to exert its power while con- 

 ditions remain favorable. Ferments act on the molecules of matter, splitting them 

 up, disturbing their peace. They are formed in the bodies of man and animals, and 

 are found in seeds. The venom of serpents, the poison of the tarantula and centi- 

 pede, are ferments. 



