a raising agent used in breads, cakes, and biscuits. It consists of a mild acid and a mild alkali which react together when wetted, generating carbon dioxide which forms bubbles in the dough. The reaction begins at once, so there is no need to leave the dough to ‘ripen’ as when using yeast.
The alkaline component of baking powder is usually bicarbonate of soda, also known as sodium bicarbonate (NaHCO3) and as baking soda. The first type, invented in the USA in 1790, was ‘pearl ash’, potassium carbonate prepared from wood ash. This provided only the alkali; the acid had to come from some other ingredient, for example sour milk. Pearl ash reacted with fats in the food, forming soap which gave an unpleasant taste. Soon it was replaced by bicarbonate of soda, which still reacts in this way but to a much smaller extent. An American name used for either of these alkali-only agents was saleratus.
True baking powder, containing both bicarbonate of soda and an acid, was introduced around 1850. The acid was cream of tartar or tartaric acid, both of which conveniently form crystals. This was mixed with a little starch to take up moisture and so keep the other components dry, so that they did not react prematurely. A disadvantage of this mixture was that it sprang into rapid action as soon as it was wetted; so the dough had to be mixed quickly and put straight into the oven before the reaction stopped.
Modern baking powder still uses these substances, but some of the cream of tartar (or tartaric acid) is replaced with a slower acting substance such as acid sodium pyrophosphate. This hardly reacts at all at room temperature, but speeds up when heated, so that bread and cakes rise well in the oven.
The starch in baking powder is not fully effective in keeping it dry, so that the components react together slowly in storage and the powder gradually loses its effect. Any that has not been used within a few months should be discarded.
Alan Davidson was a distinguished author and publisher, and one of the world's best-known writers on fish and fish cookery. In 1975 he retired early from the diplomatic service—after serving in, among other places, Washington, Egypt, Tunisia, and Laos, where he was British Ambassador—to pursue a fruitful second career as a food historian and food writer extraordinaire. Among his popular books are Seafood of South-East Asia, North Atlantic Seafood, and Mediterranean Seafood. In 2003, shortly before his death, he was awarded the Erasmus Prize for his contribution to European culture.
