Preservatives

Which preservative works depends on pH and on the target organism. Benzoic Acid and Sodium Benzoate act only in acidic products, losing most of their effect above about pH 4.5, which confines them to soft drinks, pickles and sauces. Sorbic Acid and Potassium Sorbate stay active to a higher pH, near 6.5, and so reach into bakery, cheese and dressings. The salts are the soluble forms and the free acids only sparingly soluble, so the process often decides the choice.

The others are more specific. Calcium Propionate and Sodium Propionate act mainly against mould and rope forming bacteria in bread, and the calcium salt is preferred where sodium load or dough strength matters. Natamycin acts on moulds and yeasts but not on bacteria, and is applied to the surface of cheese and cured meat. Sodium Diacetate combines acidity with antimicrobial action in dry seasonings.