Baking powder

It releases carbon dioxide when moistened and heated, making the batter rise and giving the crumb a lighter texture. It is a raising agent, not a flavouring.

A common guide is about 5 g (one level teaspoon) for every 125 g of plain flour. Too much can make a cake rise quickly and then sink, or leave a bitter, soapy taste.

Not spoon for spoon: baking powder contains an acid as well as bicarbonate, while bicarbonate of soda needs acidic ingredients such as yoghurt, lemon juice or buttermilk to react. If you substitute, the recipe may need its acid and liquid adjusted.

Not for a yeasted loaf: baking powder gives a quick rise but does not create the dough structure or flavour produced by yeast during proving. It works well in quick breads, scones and soda-style loaves instead.

Stir half a teaspoon into a little hot water; it should fizz vigorously straight away. If there is little or no bubbling, replace it, as old powder may leave cakes dense.

Keep it tightly closed in a cool, dry cupboard, away from steam and moisture. A damp spoon or a poorly sealed tin can make it react before it reaches the batter.

Double-acting powder releases some gas when mixed with liquid and more in the oven as it heats. The name refers to those two stages; recipes generally use it in the same way as ordinary baking powder.

Yes. Mix about 5 g (one level teaspoon) of baking powder thoroughly into each 125 g of plain flour, then sift the mixture to distribute it evenly. Add salt separately if the recipe calls for it.