Salting

Salting as a means of preserving food (see also preservation), has been practised since antiquity. The salt most used is common salt, sodium chloride, but saltpetre (see nitrates and nitrites), which consists of potassium nitrate and sodium nitrate, has similar effects. For some purposes ‘dry-salting’ is appropriate, for others the use of brine, which is salt in solution.

In its role in preservation of foods, salt operates mainly by its effect on osmosis, which is the passage of water through ‘semipermeable membranes’ such as the cell walls of plant or animal tissue, living or dead. A semipermeable membrane lets water through but blocks the passage of the bigger molecules of substances dissolved in it. When such a membrane has a strong solution on one side and a weak one on the other, water is drawn through it in one direction only, from the weak solution to the strong one, which it dilutes. This pull is called ‘osmotic pressure’.