FREE INSTITUTE OF SCIENCE g 



THE CHEMISTRY OF BREAD-MAKING 



The early discovery of acid potassium tartrate (potassium acid tartrate) , 

 commonly called "cream of tartar," in grape- juice and its economic production 

 as a by-product in wine-making, was due to the fact that it is less soluble in 

 alcoholic than in aqueous liquids and separates out during the fermentation 

 of the must as a crystalline deposit. The crude substance is known com- 

 mercially as argol. It was at first, and is still, often used empirically with one 

 of the forms of saleratus to produce a leavening effect. The fact that it occurs 

 in a solid form of great purity and marked permanence led to its early use in a 

 mixture with sodium bicarbonate to produce what is commonly called baking- 

 powder. Baking-powders are more largely used in preparing cakes or biscuit 

 than for the preparation of loaf bread, although it is quite possible to use them 

 for such purpose. They are of three well-known types. First, the tartrate 

 powders, in which cream of tartar, KHC4H4O6, or tartaric acid, H2C4H4O6, 

 serves as the acidic element. Second, the phosphate powders, in which calcium 

 acid phosphate, CaH4(P04)2, or sodium acid phosphate, NaH2P04, is used 

 for this purpose. Third, those in which compounds of aluminum, as com- 

 mon alum (aluminum and potassium sulfate, [K2AI2 (804)4]), ammonium alum 

 (aluminum and ammonium sulfate, (NH4)2Al2 (804)4), or sodium alum (alumi- 

 num and sodium sulfate, Na2Al2 (804)4), are employed to liberate the carbon 

 dioxid from the sodium carbonate. In all these, sodium acid carbonate is 

 used as the gas-Hberating constituent because it is lower in price than the 

 potassium salt and also because it liberates more gas than an equal weight of 

 the potassium salt. There is also a large proportion of inert or diluting ma- 

 terial, usually corn-starch, wheat flour or some other absorbent material, added 

 for the purpose of keeping the acidic and gas-liberating ingredients mechanic- 

 ally separated, for if these come into close contact in the presence of even 

 minute proportions of moisture, as are always absorbed by substances kept in 

 any but hermetically sealed containers, the reaction slowly proceeds, and when 

 the powder is to be used, it might not have any leavening power, because the 

 gas would have already disappeared. In some few powders magnesium car- 

 bonate is used, partly as a moisture absorbent and partly for its carbon dioxid 

 yielding properties. In the tartrate powders the reactions are as follows : 



When tartaric acid is used : 



