Salting & Curing

Salting preserves meat, fish and vegetables by drawing water out of them and out of the microbes that would spoil them. People were boiling brine for salt in eastern Europe by the sixth millennium BCE, and salted pork, herring and cod fed armies, sailors and cities until refrigeration.

What it is

Salting, or curing, is one of the oldest ways of keeping food. Meat or fish is rubbed with dry salt or soaked in brine until it holds so little free water that spoilage bacteria cannot grow. Often the food is then dried, smoked or left to mature. Vegetables can be salted lightly instead, so that useful lactic bacteria ferment and sour them, as in sauerkraut.

The plate gathers the methods of a European larder before refrigeration: coarse salt, pork legs buried in a salting trough, herring packed in a barrel, hams hanging to dry, and split cod drying on a rack.

How it works

Every microbe needs water it can use. Food scientists measure that with water activity, which is 1.0 for pure water and falls as salt or sugar binds water. The limit differs from one microbe to another, and some food-poisoning bacteria still grow at fairly low values, but the great majority of microbes stop multiplying below about 0.90. A saturated salt brine sits near 0.75.

Rock salt grows in cubes; a crystal that grows faster along its edges than across its faces becomes a stepped “hopper”.

When salt touches meat or fish, water flows out of the tissue towards the more concentrated salt solution, while salt slowly moves in. Bacteria on the surface lose water the same way: their cell contents shrink away from the wall and they stop growing or die. The deeper the salt goes and the more water leaves, the longer the food keeps. Heavily salted cod or ham can last for months or years, but has to be soaked in fresh water, in the refrigerator, before cooking.

Salt does not sterilise. Some dangerous bacteria tolerate it well, Staphylococcus aureus among them, and Clostridium botulinum, which grows without air, survives as spores in poorly cured meat and fish. Most modern meat cures therefore contain nitrite, which slows the growth of botulinum and keeps cured meat pink. Older recipes used saltpetre, which bacteria in the cure turn into nitrite.

Light salting works differently. With about 2 to 2.5% salt, cabbage keeps enough water for lactic acid bacteria, which tolerate salt better than most spoilers. They turn its sugars into lactic acid, and the acidity preserves the food.

How to build it

Curing meat at home safely needs a tested recipe, measured curing salt and a cool, controlled room. The safest place to start is with salt and cabbage: sauerkraut.

Prepare the cabbage. Take firm, fresh heads, remove the outer leaves and the cores, and shred finely, about 5 mm wide. Weigh it.

Salt it. For every 2.25 kg of cabbage, mix in 3 tablespoons of canning or pickling salt (salt without iodine or anti-caking agents), about 2 to 2.5% by weight. Pack it hard into a clean crock or wide jar, a handful at a time, pressing until the salt draws out the juice.

Cover and weigh it down. The cabbage must stay under its own brine at all times. If the juice does not cover it, add brine at once, made with 1½ tablespoons of salt for every 950 ml (one US quart) of boiled and cooled water. Lay a plate on top with a weight, such as a sealed bag of brine, and cover with a cloth.

Let it ferment. At 21 to 24 °C the cabbage takes about three to four weeks, at 15 to 18 °C five to six weeks. Below 15 °C it may not ferment; above 24 °C it can turn soft. A thin white film may form on the surface: skim it off. The kraut is ready when the expected time has passed, the bubbling has stopped and the cabbage tastes clearly sour throughout. It then keeps for months in the refrigerator.

Safety. Keep vegetables under the brine at all times and use clean equipment. Throw the whole batch away if fuzzy or coloured mould appears anywhere, or if the kraut turns slimy, pink or dark, or smells rotten. Do not improvise cured meat or fish: botulism is rare but deadly, and nitrite curing salt is poisonous in excess. Use only the curing product, dose and weighing precision a tested recipe specifies, label it and keep it away from children. Cured foods carry a lot of salt; anyone told to limit salt should soak them well or avoid them.

History and evolution

Briquetage: brine was boiled in coarse clay troughs over a fire, and the troughs were broken to free the salt cakes.

Salt was being made long before writing. At Poiana Slatinei near Lunca, in north-eastern Romania, a brine spring about six times as salty as seawater is surrounded by a mound of ash and burnt earth some three metres high, left by people who boiled the brine with fire from about 6050 BCE. The excavators do not know whether that salt went to preserving food, to livestock or to trade, so the date marks the oldest known salt-making, not the first salted food.

In later prehistoric Europe, brine was boiled in coarse clay vessels set on clay props over a fire, a method called briquetage. The vessels were broken to free the salt cakes, and heaps of their fragments still mark the sites. At Hallstatt in Austria, people mined rock salt from the Bronze Age, and in the 13th and 12th centuries BCE they salted pork on a large scale in timber vats sunk into the ground, eight of which are now known.

Salt cod, beheaded, split and dried, keeps for years and must be soaked in the refrigerator for a day or more before cooking.

The Greeks salted fish as tarichos and the Romans called salted meat and fish salsamentum; in the second century BCE, Gaul sent salt pork to Rome in large quantities. In Catholic Europe, salted fish, and dried salt cod above all, became the everyday food of Fridays and Lent, when meat was forbidden.

Cod from Newfoundland was already being salted for European markets in the sixteenth century, and in the seventeenth, cheap salt from southern Europe made salting worthwhile for the fishing nations of the north; salt cod became one leg of the Atlantic trade. Canning, from the early nineteenth century, and refrigeration in the twentieth took over much of the work, yet ham, bacon and salt fish are still cured with salt, and sauerkraut is still fermented in its own brine.