Arawa Manu, of Pt Chalmers School, asks :-

Why do some medicines tast sour?

Rob Ledger, a pharmacist with the School of Pharmacy, Otago University, responded.

Medicines that contain acids will taste sour. In this they are like all substances that contain acids such as the malic acid of apples, citric acid of lemons or acetic acid of vinegar.

The sour taste will be detected by receptors within taste buds at the sides of the tongue. The acids must really act like acids in the mouth, that is they must be strong enough to dissociate in the mouth.

Many medicinal compounds and pharmaceutical additives fulfil this criterion. Some such compounds can have more than one primary taste, for example, citric acid tastes both sour and sweet where the sweet taste is detected at the tip of the tongue.

The sour taste of a medicine can be masked by the addition of syrup or by enclosing the medicine in a capsule which dissolves in the stomach so the taste buds in the tongue never detect the sour medicine within.