Science Questions

What makes a cake rise? Isy, Australia

Self-raising flour contains baking powder, which is usually a mixture of bicarbonate of soda, crème of tartar and something called calcium aluminium phosphate.  Bicarbonate of soda has lots of carbon dioxide locked up in it, which is let out by reacting with an acid.  Crème of tartar becomes tartaric acid when it gets wet, so these then react together and produce bubbles of carbon dioxide in the cake, making the cake rise.  Calcium aluminium phosphate only becomes acidic when it gets to a certain temperature, giving extra bubbles, and so extra rising, while the cake bakes.

August 2007