Uses of salt

Brines and cured meats

Up to the 18^th century, when people began using salt for "culinary" purposes, most of the salt produced was used to preserve food by curing. It was used mainly for meat, but also a lot of fish. For meat, you need to add at least 10% of the weight of the meat that is to be cured in salt (i.e. for the average pig, at least 5 to 6 kilograms of salt).

Dairy products (such as butter and cheese, which keep longer) were also salted. In the Middle Ages, there was one pound of salt for every 10 pounds of butter, and 5 to 10% of cheese was made up of added salt. Finally, brines were produced to preserve foodstuffs (such as vegetables) in a salty solution.

We do not have precise estimates of the quantities of salt used in this way. In the Middle Ages, from the 13^th century onwards, it accounted for between 50 and 60% of the salt produced.

Culinary salt

Only a small percentage of the salt produced was used to season food. For pre-industrial European societies, it is estimated that an annual quantity of 3.5 to 4 kilos was artificially introduced into each individual's diet.

We have no comparable estimates for ancient times. In his work De Agri Cultura, the Roman author Cato the Elder states that a quantity of one modius of salt (i.e. 8.75 litres, or around 7 kilos) per person per year was needed to maintain the community of slaves on a small agricultural estate. This figure undoubtedly takes into account the servile workforce's families.

Salt in crafts and manufacturing

These are marginal uses of salt in terms of quantity, accounting less than 10% of the mass of salt produced. They are often of great economic and technical importance.

• In the case of tanning, salt is used for its dehydrating and preserving properties, preventing the hides from rotting. Tanning requires 25 to 50% of the weight of the hides in salt; a coarse salt, different from the type of salt that is eaten, is used.
• In the case of glassmaking, salt is used for its ability to lower the melting point of silicates, which in turn makes glass easier to handle.
• in the case of steelmaking, salt's pickling properties are used to make soldering easier.
• Goldsmiths use the ionising properties of salt to transfer one metal to another (to silver or tin copper, for example).

Salt and medicine

The therapeutic properties of salt have been recognised since ancient times, notably by Pliny the Elder in his Natural History. The Romans used salt baths to cure skin diseases and ailments of the liver and respiratory tract.

In the Middle Ages, salt was most often used in plasters, powders or baths; it helped heal sprains and fractures, and soothed inflammation. Its drying power was also used to disinfect wounds. It was also used in hunting, to heal dogs bitten by wild animals by immersing them in salt water baths.