FREE INSTITUTE OF SCIENCE g 



THE CHEMISTRY OF BREAD-MAKING 



Theoretically, this is the least objectionable of all chemical methods of 

 leavening, for the mineral residue left as the result of the reaction is salt, which 

 is normally added to bread, and may as well be added in this way. The method 

 is not suitable for use in the home, however, for it requires the services of a 

 chemist to mix the reacting substances in the proportions needed. There is 

 no solid compound in which the acidity of hydrochloric acid is available, as 

 is the case with some other acids, and no baking-powder is possible giving the 

 above reaction or one similar to it in its unobjectionable character. 



Another old form of chemical leavening agent still sometimes used by 

 bakers, and more rarely in the home, is ammonium carbonate. Theoretically 

 this salt is (NH4)2C03, which, under the influence of the heat in baking, is 

 dissociated into 2NH3+ 2CO2+ H2O. Practically, as found in the market, 

 the salt is more complex, consisting of a molecule of acid ammonium carbonate 

 (ammonium bicarbonate) and a molecule of ammonium carbamate, as follows : 



NH4HCO3 . NH4NH2CO2. 



This also dissociates under the heat of a baking temperature, yielding 

 3NH3+ 2CO2+ H2O. In both these dissociations all the resulting products 

 are volatile and are liberated and dissipated during the baking process, the 

 carbon dioxid and ammonia both being gases, produce the leavening effect 

 desired. If the product is underdone, a slight odor of ammonia is noticeable 

 in the baked product. The commercial ammonium carbonate was so widely 

 used at one time as to be known as "bakers' ammonia." Its disuse has been 

 partly due to lack of skill and care to secure a product free from the objection- 

 able odor of ammonia, and probably more largely due to the discredit which 

 attached at one time to the ammonium salts as a class, which, before the days 

 of their manufacture as a by-product of illuminating gas, were usually obtained 

 from decomposing animal refuse. All ammonium salts of commerce are now 

 obtained by the distillation of coal and are free from the above-mentioned 

 objection. 



At this same early period, before the days of so-called "baking-powders," 

 now used so largely as leavening agents, there were two commonly used 

 salts employed empirically to produce a chemical leavening effect. The first 

 one of these was potassium acid carbonate (potassium bicarbonate), KHCO3, 

 which, by virtue of the fact that it evolves a gas when treated with an acid, 

 was called "sal aeratus," usually shortened to "saleratus." Later the 



