alkali an odd-looking word which comes more or less straight from the Arabic al-kali, meaning the calcined ashes of plants such as saltwort. In food science it means ‘any substance which neutralizes or effervesces with acids and forms a caustic or corrosive solution in water’ (NSOED). It can also mean a soluble salt (or mixture of such salts) of an alkaline nature. See acids, and also pH for an explanation of the scale by which the acidity or alkalinity of a substance is measured.
Very few foodstuffs are alkaline. Indeed, McGee (1984) remarks that ‘egg albumen and baking soda are the only alkaline ingredients to be found in the kitchen’. However, a number are almost neutral, e.g. milk. So adding milk (or yoghurt) to a mixture will normally reduce the acidity of the mixture.