FREE INSTITUTE OF SCIENCE g 



THE CHEMISTRY OF BREAD-MAKING 



When these powders are properly made, no alum remains after the leaven- 

 ing reaction, though by misleading advertisements by firms making other 

 types of powders, many persons are led to beheve the contrary. There re- 

 main, however, in the food, as foreign substances, insoluble aluminum hy- 

 droxid and the soluble sodium sulfate; the latter, commonly known as Glauber's 

 salt, used as a cathartic, particularly in veterinary practice. Soluble ammo- 

 nium and potassium sulfates remain in the food made from those alums respec- 

 tively. 



A modification of alum powder has been manufactured which contains a 

 mixture of one of the alums and monocalcic phosphate. The reaction in this 

 case is somewhat different, and with the sodium alum (the one most commonly 

 used in alum powders, as it is the cheapest and is known to the baking-powder 

 trade simply as "S. A. S.," which is an abbreviation of its chemical name, 

 sodium aluminum sulfate) is as follows : 



Na2Al2(S04)4+CaH4(P04)2+4NaHC03->4C02+4H20-|-3Na2S04+CaS04-I-Al2(P04)2 



Sodium Calcium acid Sodium acid Carbon Water Sodium Calcium Aluminum 



aluminum phosphate carbonate dioxid sulfate sulfate phosphate 



sulfate 



In this case the insoluble residue is aluminum phosphate, while the other salts 

 are the soluble sodium sulfate and the difficultly soluble calcium sulfate. 



As may be readily appreciated by any person of intelligence and discernment, 

 all the chemical leavening agents reactions of which have just been described 

 are open to the same objection, i. e., that a foreign salt is formed in the food 

 in which they are used. It, therefore, is merely a question of which is the 

 least objectionable. The choice in this respect lies closely between the 

 phosphate and tartrate powders, with the combined alum and phosphate 

 powder next and the alum powders last. Any of them might be harmful if 

 eaten every day. 



3. Leavening the Dough by the Use of Yeast. — Yeast is a unicellular organ- 

 ism of minute size (about -^^-^ of an inch in diameter) , belonging to the vege- 

 table kingdom. Many species have been identified, only a few of which are 

 of value in bread-making. That most frequently employed is Saccharomyces 

 cerevisicE (literally, the sugar fungus of beer). Each individual yeast cell is 

 capable of reproduction and requires nourishment for its growth and multi- 

 plication during which it exercises the functions that make it valuable in 

 bringing about fermentation. Yeast requires a variety of nutrients, just as 



