Propionic Acid
What it does
Prevents mould in bread.
How it's made
Synthesised or from fermentation.
Propionic acid is a preservative particularly good at stopping mould and "rope" bacteria in bread and other baked goods, which is why it and its salts are the classic anti-mould additives for packaged bread. It occurs naturally in some fermented foods, including certain cheeses, where propionibacteria produce it.
For food use it is made by chemical synthesis from petrochemical feedstocks — commonly by processes that build the small propionic acid molecule from ethylene-derived intermediates. A fermentation route using propionibacteria also exists, mirroring how the acid arises naturally in cheese.
The acid is purified by distillation into a clear liquid with a pungent smell. Because the free acid is volatile and strong-smelling, it is often used as its calcium or sodium salt in bread, where it releases active propionic acid to hold back mould, considerably extending the shelf life of the loaf.
Possible reactions
May worsen behaviour/irritability in some children; occasional migraine.