Sorbic Acid
What it does
Inhibits mould and yeast.
How it's made
Synthesised or from rowan berries.
Sorbic acid is a widely used preservative that inhibits the growth of moulds, yeasts and some bacteria, extending the shelf life of cheese, baked goods, dried fruit, drinks and many other products. It occurs naturally in the berries of the rowan (mountain ash) tree, from which it was first isolated.
For food use it is made by chemical synthesis rather than extracted from berries. The usual route reacts crotonaldehyde with ketene (or uses related building blocks) to construct the sorbic acid molecule, which is then purified. Synthesis produces the identical compound reliably and cheaply in the quantities the food industry needs.
The acid is purified and crystallised into a white powder. It works best in slightly acidic foods, where it is most effective at stopping mould and yeast, and it is often used as its more soluble salts (such as potassium sorbate) when a form that dissolves easily in water is required.
Possible reactions
Rare skin irritation.