Kala namak

Kala namak ("black salt" in Urdu, Urdu: کالا نمک, Hindi, Hindi: काला नमक) is a kiln-fired rock salt with a sulphurous, pungent smell used mainly in the countries of South Asia. It is also known as "Himalayan black salt", bit noon, bire noon, bit loona, bit lobon, kala loon, sanchal, kala meeth, guma loon, or pada loon, and is manufactured from the salts mined in the regions surrounding the Himalayas.

The condiment is composed largely of crystalline sodium chloride heated with charcoal and several other herbal components lending the salt its color and smell. The smell is mainly due to its sulphur content; the salt is heated in presence of many herbal components and also contains greigite (Fe₃S₄, Iron(II,III) sulphide). When whole, the salt is brown and black. When ground into a powder, its color may range from pink to black-brown to dark black.

Kala namak has been praised in herbal science and used for its perceived medical qualities.

The raw material for producing kala namak was originally manufactured from natural halite from mines in Northern India in certain locations of the Himalayas, salt manufactured from the North Indian salt lakes of Sambhar or Didwana.

Traditionally, the salt was transformed from its relatively colorless raw natural forms into the dark-colored commercially sold kala namak through a reductive chemical process that transforms some of the naturally occurring sodium sulphate of the raw salt into pungent hydrogen sulphide and sodium sulphide. This involves firing the raw salts in a kiln or furnace for 24 hours while sealed in a ceramic jar with charcoal along with small quantities of harad seeds, amla, bahera, babul bark, or natron. The fired salt melts, the chemical reaction occurs, and the salt is then cooled, stored, and aged prior to sale. Kala namak is prepared in this manner in northern India with production concentrated in Hisar district, Haryana. The salt-crystals appear black and are usually ground to a fine powder that is purple.

Although kala namak may have traditionally been chemically produced from impure deposits of salt (sodium chloride) with the required chemicals (small quantities of sodium sulphate, sodium bisulphate, and ferric sulphate) and charcoal in a furnace it is now common to simply add the required chemicals to pure salt before firing. Reportedly, it is also possible to create similar products through reductive heat treatment of salt, 5-10% of sodium carbonate, sodium sulphate, and some sugar.

Kala namak consists primarily of sodium chloride and trace impurities of sodium sulphate, sodium bisulphate, sodium bisulphite, sodium sulphide, iron sulphide, and hydrogen sulphide.

Sodium chloride provides kala namak with its salty taste, iron sulphide provides its dark violet hue, and all the sulphur compounds give kala namak its slight savory taste as well as a highly-distinctive smell, with hydrogen sulphide being the most prominent contributor to the smell. The acidic bisulphates/bisulphites contribute a mildly sour taste. Although hydrogen sulphide is toxic in high concentrations, the amount present in kala namak used in food is small and thus its effects on health are negligible.