Cream of tartar
A white powder which is sold in a small tub with the baking goods. It is used as a raising agent and is the acidic component of baking powder.
Uses: Cream of tartar is added to cake and scone mixtures to help them rise - it reacts with heat and moisture to produce carbon dioxide molecules which expand and cause the mixture to rise.
To store: Keep in a cool dark, dry place for up to 1 year.
To use: Only a small amount of cream of tartar is used in recipes - usually no more than 1 tsp (but refer to the recipe you are following) and it is important to measure it out carefully. Cream of tartar is usually sieved with the flour in a recipe.