Salting

Water activity — the idea underneath everything

Microbes need water. Not water in the food in the sense of how wet it feels, but water that is chemically available to them — free to move, free to take part in reactions. Food scientists call this water activity.

Salt binds water to itself. Dissolved salt holds water molecules in its hydration shells, so that water is present but no longer available. A heavily salted food can be visibly wet and still be, from a bacterium's point of view, a desert.

It also works the other way round, on the microbes themselves: a cell sitting in a concentrated salt solution loses its own water by osmosis and cannot function.

This is exactly the same principle as drying, and exactly the same principle as sugaring in a jam. Three methods, one mechanism — reduce available water below what microbes can work with.

Dry salting against brining

Two ways of applying the same thing, with different results.

Dry salting

Salt applied directly to the surface. Draws liquid out of the food, which either drains away or forms a brine in place. Gives a firmer, denser, more concentrated result. Used for curing meat and fish, and for sauerkraut.

Brining

Food submerged in salt water. Salt moves in, and less water comes out — the food may even gain weight. Gives a juicier, more evenly seasoned result. Used for meat before roasting, olives, and most vegetable ferments.

Dry brining

Salt on the surface, left long enough for the drawn-out liquid to dissolve it and be reabsorbed. Common for poultry and steak. Seasons deeply without adding water.

Which for what

Preserving generally wants dry salting, because the aim is removing water. Cooking generally wants brining, because the aim is seasoning without drying.

Where salting is still doing real work

• Salt cod and salt fish, which are preserved to the point of needing days of soaking before use. The oldest surviving example of the method used at full strength.
• Cured meats — every ham, bacon and salami begins with salt, and salt does the preserving even where smoke and drying follow.
• Olives, which are inedibly bitter raw and are cured in brine or dry salt for months.
• Preserved lemons, packed in salt until the peel goes soft and the flavour turns from sharp to floral and savoury.
• Salted egg yolks, buried in salt until firm enough to grate.
• Anchovies and fish sauce, where salting keeps spoilage out while the fish digests itself.
• Every vegetable ferment, where salt is not the preservative but the referee — see salt in fermentation.
• Salting aubergine or cucumber before cooking, which is drawing water out for texture rather than for keeping.

Salting as a cooking technique rather than a preserving one

Most salting done in a modern kitchen is not preserving anything. It is using the same osmotic mechanism for a different end.

Brining meat before roasting adds water and seasoning and gives the muscle proteins a structure that holds onto moisture during cooking. The result is a juicier bird, and the mechanism is salt disrupting protein structure rather than salt preserving anything.

Dry-brining a steak — salting it well ahead — draws moisture to the surface, where it dissolves the salt and is drawn back in. It seasons through and leaves a drier surface, which browns better.

Salting aubergine, courgette or cucumber draws out water so the food fries rather than steams, or so a salad does not go watery.

Salting pasta water is seasoning, and nothing else. It does not raise the boiling point to any degree that matters.

Common questions