In the presence of water, one of the two acids contained in baking powder will react with the sodium
bicarbonate present to produce bubbles of CO2. (Baking powder thus often contains starch, which acts
to prevent early reactions between the bicarbonate and acid molecules, by absorbing moisture and
helping keep the powder dry). The second acid present in baking powder reacts with sodium
bicarbonate at higher temperatures, to produce more bubbles of CO2.during the beginning of the
baking process. When using baking soda, the sodium bicarbonate will react with acid present in the
cake mixture to produce CO2. Baking powder and baking soda are more efficient raising agents than
yeast, and produce CO2 much faster, however they do not improve the taste and flavour of the dough
in the way that inclusion of yeast does.
Gas can be incorporated into a cake mixture mechanically by a process called creaming. Creaming
involves incorporating air bubbles into the butter by beating the butter with an electric mixer. Then
sugar (granulated, not powdered) is sprinkled slowly into the butter. As the sharp sugar crystals cut
into the butter structure, tiny pockets are formed between the butter crystals. These pockets fill with
air, and as the mixer blades pull more butter over the top, these pockets get sealed in place.
Alternatively, air bubbles can be introduced by incorporating a previously aerated mixture, such as
whipped cream or whipped eggs, which is carefully introduced into the mixture. Cake mixtures should
not be over-mixed during the preparation, as this will cause them to lose CO2 or the air incorporated
As the cake is cooked, the CO2 or the air incorporated during mixing will expand, and the water
contained in the mixture will evaporate, and this will cause the dough to rise. These bubbles are held
in the mixture by the network that forms around the bubbles as the denatured flour proteins coagulate,
and surrounds and holds the air bubbles in place. The supporting network is not as strong as it is in
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