Oxalic Acid

HOOC–COOH, is naturally present in various foodstuffs, including sorrel, rhubarb, spinach, and chocolate. It is toxic in large doses, at levels which are not reached in normal eating patterns; but rhubarb leaves, if they were eaten, could deliver a harmful dose.

There is a persistent belief that the oxalic acid in sorrel is capable of softening the small bones of fish to such an extent that they ‘melt away’ or at least can be eaten without discomfort. Jaine (1986b) tested the hypothesis, using both sorrel leaves (which are traditionally used in cooking bony fish like shad) and various dilutions of oxalic acid, and established that any effect is insignificant. However, sorrel remains an excellent accompaniment to fish in the dishes where tradition calls for its use. The softening of fish bones can be and is achieved to some extent by prolonged cooking, whether with or without sorrel.