baking powders defined in 1909 yearbaking powders - baking powders;
baking powders - The following is condensed from a lecture on the chemistry of confectioners' materials, delivered by William Jago, before the Society of Arts.
Ammonium CarbonateAmong the first of aerating agents is the solid commercial ammonium-carbonate, called by the confectioner, "ammonia" or "volatile." This salt may be represented by the formula 2(NH4) 2 CO3 CO2 and is a mixture of the carbonate and carbamate of ammonium. The compound has an ammoniacal smell and an acrid burning taste. On the application of heat, "volatile" is decomposed into gaseous ammonia, water, and carbon-dioxide gas. The commercial salt should be almost free from non-volatile bodies, and good specimens will leave only a trace of fixed foreign matter after being subjected to a temperature of 100° C., the actual quantity being from 0.04 to 0.4 per cent. As the composition of the salt varies, its strength may be determined by an estimation of the alkalinity, titrating with sulphuric acid, and using methyl-orange as an indicator. The salt is continuously losing ammonia, and so becomes weaker. Commercial samples vary in strength from an alkalinity equivalent to about 80 to one of about 93 per cent, of the pure salt. If ammonium carbonate be mixed with the other constituents of a dough, there is very little change until the goods are placed in the oven. With a rising temperature, the liberated carbon dioxide and ammonia gases distend the mass and so produce the desired lightness. When withdrawn from the oven such goods may smell and taste most strongly of the ammonia. With small articles of a porous texture, this smell soon completely passes off, but with larger ones this does not occur at all so readily, and for this reason " volatile " has to be used sparingly and cautiously by the confectioner, and has practically passed out of use in preparations sold for domestic use.
Sodium BicarbonateSodium Bicarbonate is another salt capable of giving off gas, under the action of heat alone. This compound NaHCO3, then becomes the normal carbonate, Na2CO3, with the evolution of steam and carbon dioxide. A temperature of 38° C. (100° F.) is sufficient to complete this change. Sodium bicarbonate has only a slight brackish flavour, but the normal carbonate has a strong alkaline taste. For this reason, and because only half its gas is evolved by heat, the bicarbonate is but seldom used alone. The objectionable flavour is, however, the much more pressing reason of the two, because a double quantity of the carbonate would cost much less than the amount of acid necessary to act on the one portion of carbonate only. Commercial bicarbonate of soda is obtained of a high degree of purity, and usually gives an alkalinity very nearly equivalent to 100 per cent, of the pure salt. At times figures are obtained which even go beyond this, and one is confronted with, perhaps, apparently 103 per cent. In such cases the explanation lies in the fact that the salt contains more or less sodium carbonate as impurity. In the analysis of the bicarbonate it is always well to search for, and estimate approximately if necessary, the quantity of normal carbonate present. In using bicarbonate great care must be taken that the salt is finely ground and intimately mixed with the flour and other constituents of the dough. Neglect of such precautions leads to the formation of small masses of the normal carbonate during baking, and these in turn act on the proteid constituents of flour with the production of a yellow stain or spot. Further, flour thus acted upon by normal carbonate evolves an unpleasant soapy odour. Like ammonium carbonate, the bicarbonate of soda only commences to evolve gas when subjected to the heat of the oven.
Tartaric AcidWhen sodium bicarbonate is treated with an acid, the whole of the carbon-dioxide gas is evolved, and the corresponding salt formed. Of all acids, that found most convenient by the confectioner is tartaric acid, either in the free state or as its acid potassium salt. Tartaric acid is widely distributed in nature, and is manufactured from some of its compounds occurring in grape juice. The acid occurs in commerce as a fine white powder, having a clean acid flavour, and is very soluble in water. When tartaric acid and sodium bicarbonate are mixed in with flour in equivalent quantities, the result, by moistening with water, is, that the acid attacks the carbonate, liberating all its carbon-dioxide, and forming normal sodium tartrate. This latter salt is comparatively tasteless, and the presence of the quantity produced as a residue from the amount of acid and soda necessary for the aeration of an average dough is not sufficient to injuriously affect the flavour of the resultant goods. The action of tartaric acid and the bicarbonate, or more shortly "soda," commences immediately on the addition of water, and, for that reason, it is well to get the dough into the oven as speedily as possible. Then, with the greater heat, solution of the two re-agents and their consequent mutual action, go on with augmented speed. Tartaric acid being somewhat expensive, it is important that no waste of it should occur, and as all, mixed in a dough, that is in excess of the equivalent of the soda is lost, it is well to remember that the proper proportion is 15 parts by weight of tartaric acid to 17 parts of soda. Tartaric acid should, on analysis, show an acidity equal to 99 (or upwards) per cent, of pure acid, and the ash should not exceed 0'25 per cent. Tartaric acid is said to have been adulterated with alum and acid potassium sulphate; but both these would be detected by an abnormally large percentage of ash, and also by the presence of sulphates.
Cream of TartarNot only is tartaric acid itself employed, but so also is its acid potassium salt, cream of tartar. Cream of tartar exists in the crust or tartar deposited by wines on keeping, and is obtained by a process of solution, purification, and re-crystallisation. The salt occurs commercially as a white powder, and differs from tartaric acid in that it is only very slightly soluble in cold water, one part of the salt dissolving in about 250 of water at 50° F., whereas boiling water dissolves it in the proportion of one part of "cream" in 15 parts of water. To the confectioner, this is a most important property, because as a result a mixture of cream of tartar and bicarbonate of soda, as an aerating agent, is almost inactive in the cold. Doughs made with this mixture, undergo little or no aerating change until placed in the oven. Then the rise in temperature results in solution of the cream, and its consequent action on the bicarbonate. This salt therefore becomes active just at the time when such activity is most effective. The salt resulting from the action of these two re-agents on each other, is well known under the name of "Rochelle salt." It possesses only a bland saline taste, and hence does not sensibly affect the flavour of goods in the manufacture of which "soda and cream" are employed.
Sulphates and PhosphatesTartaric acid has been mentioned as the one of most importance to the confectioner. Among more or less successful substitutes are acid potassium sulphate, acid calcium and potassium phosphates, and phosphoric acid. The three former are obtainable as white powders, and, mixed with starch in various proportions, are used as substitutes for tartaric acid and cream of tartar respectively. In older confectioners' recipes alum is sometimes included as an ingredient; this body has a powerful acid reaction, and with soda can be used as an aerating agent. In view of the injurious nature of alum, its employment need only be mentioned in order to condemn it, and to point out that some non-injurious form of acid should be used in its stead.
Following are recipes for compounding baking-powders: