How table salt is made

Only about 17.5% of the world's salt goes into food. The rest goes to chemical plants, road de-icing and water treatment.

stations: 5
things upstream: 2
raw sources: 2
step from the ground: 1

The short version

Table salt comes from seawater or underground salt beds. Seawater is evaporated in shallow pools, and deep deposits are mined or dissolved into brine and boiled down. Chemicals are added to drop out magnesium and calcium. The brine is evaporated in vacuum pans, then iodine and an anti-caking agent are mixed in.

Find the salt

Salt comes from mines in ancient seabed deposits, from spring water, or from seawater, which carries about 35 g of dissolved salts per kilogram. Deposits can also be dissolved by pumping water underground and bringing the brine up.

Goes in
Rock salt Seawater
Clean the brine

The raw salt is dissolved and treated with chemicals that precipitate most of the impurities, mostly magnesium and calcium salts.
Evaporate it in a vacuum pan

Multiple stages of evaporation boil the water off. In the Alberger process, a vacuum pan evaporates the brine while cubic crystals seed the solution, which grows a grainy flake salt.
Mix in the additives

Table salt often has iodine added, at 46–77 ppm in the US. An anti-caking agent such as magnesium carbonate, used since at least 1911, keeps it flowing.

46–77 ppm iodine in US salt
Dry, pack and ship

The salt is dried, screened and packed in cartons, canisters and bags.

End of the lineTable salt Next it goes into butter, cheese, margarine and 41 more.

Worth repeating

Around 6000 BC, people in what is now Romania boiled spring water to extract salt.
The Sifto mine in Ontario sits about 550 meters below Lake Huron and yields about seven million tons of salt a year.
The Khewra Salt Mine in Pakistan has 400 km of passages.