When recipes specify either table salt or kosher salt, is there really that much of a difference?
— Robert L., Medford
All salt — plain ol' table salt or fancy flakes of fleur del sel — at its most basic is simply sodium chloride. The difference is in texture and the addition or lack of minerals.
Table salt is made with very fine grains. Minerals are removed, but it usually includes an anti-caking agent, such as calcium silicate. Iodine may be added to prevent thyroid diseases in regions where diets are low in this nutrient. Not all table salts are iodized, however.
Kosher salt comes from the same source as table salt but is made with larger grains. Not necessarily a kosher product, it's used in the process of koshering — removing blood to purify meat or make it kosher — because the larger grains dissolve more slowly and are better at removing moisture from meat.
Cooks like using kosher salt because the larger grains make it easy to grab a pinch while cooking. It also doesn't have anti-caking agents, which can make brines cloudy.
You can swap the two in cooking, but taste carefully. Because table salt is finer, more grains will fit in a measuring spoon. So a recipe formulated to use kosher salt might be saltier if you make it with table salt.
Incidentally, "fleur de sel" is one of the world's rarest and most expensive salts. Literally translated from French as "flower of salt," this all-natural sea salt is harvested in Brittany from salt crust that forms on salt ponds via evaporation.
The price of $10 to $20 per pound indicates that fleur de sel's still-moist crystals are meant to be used sparingly as a garnish on finished dishes, not during cooking.
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