Calcium Propionate — Frequently Asked Questions

Handling. Propionic acid is a corrosive, strongly odorous liquid that attacks galvanised and mild steel equipment and is unpleasant to dose. The calcium salt is a neutral free-flowing powder that mixes into a feed blend without corroding the mill and without persistent odour, while delivering the same propionate chemistry.

The undissociated propionic acid crosses the fungal cell membrane, dissociates inside at the higher internal pH and disrupts energy metabolism. Because only the undissociated form can cross, activity depends on pH, being strongest in acidic conditions, though propionates remain useful nearer neutral where benzoate and sorbate have stopped working.

In feed it is a useful mineral rather than a contaminant, so the calcium is a modest benefit. In chemically leavened baking it is a problem, because calcium ions interfere with the leavening reaction and can reduce gas production and volume, which is why sodium propionate is used in those products instead.

Rope is a sticky, ripe-smelling spoilage of bread crumb caused by Bacillus species that survive baking as spores. Propionates inhibit those organisms as well as moulds, and calcium propionate is the standard preventive measure. Its selectivity matters: it suppresses the spoilage organisms while leaving baker's yeast largely unaffected.