Walnuts Changing Colour in Banana Bread

Our answer

Nigella's Banana Bread (from Domestic Goddess and on the Nigella website) uses a combination of baking powder and bicarbonate of soda (baking soda) as raising agents. Sometimes bicarbonate of soda, which is an alkali, can react with certain ingredients and make then change colour, though it is quite rare.

In this particular case it is quite unusual as baking powder is used and this will provide some acid, which normally neutralises the alkalinity of the bicarbonate of soda. However we would suggest making sure that the raising agents are distributed evenly in the flour by either sifting them all together or whisking them well with a wire whisk before using. Also use 1 teaspoon/1/2 teaspoon (5ml and 2.5ml) measuring spoons for the raising agents and use level spoonfuls. You could also try tossing the walnuts in a spoonful of plain flour (without any raising agents) before using them in the cake batter.