A measure of available water in food for microbial growth, expressed on a scale of 0 to 1. Salt reduces water activity by binding water molecules, which is why salt-cured foods resist spoilage. Most bacteria cannot grow below 0.91 aw.
Salinity
The measure of dissolved salt content in water, expressed as parts per thousand (ppt) or percentage. Ocean water averages 35 ppt salinity. The Dead Sea reaches 340 ppt, nearly ten times saltier than the ocean.
Sodium Chloride (NaCl)
The chemical compound that makes up common salt. Composed of sodium and chlorine atoms in a 1:1 ratio forming a cubic crystal lattice. Essential for human life, nerve function, and fluid balance.
Osmosis
The movement of water through a semipermeable membrane from an area of lower salt concentration to higher concentration. This is the principle behind brining meat, preserving food with salt, and salt water gargling for sore throats.
Hygroscopic
The property of absorbing moisture from the surrounding air. Salt is highly hygroscopic, which is why it clumps in humid conditions and why salt lamps can weep water. Anti-caking agents in table salt counteract this property.
Iodization
The process of adding iodine to table salt to prevent iodine deficiency disorders. Introduced in the United States in 1924, iodized salt is one of the most successful public health interventions in history, virtually eliminating goiter in developed nations.
Anti-Caking Agent
An additive used in table salt to prevent clumping. Common agents include calcium silicate, sodium aluminosilicate, and magnesium carbonate. These keep salt free-flowing but can affect flavor and cause cloudiness in brines.
