Where Kosher Salt Comes from & Why It's Called Kosher
My pantry always has three kinds of salt: fine table salt, kosher salt, and a super-flaky salt like Maldon. I use all three in different ways, depending on what I'm cooking or how I'm seasoning something. When people see my kosher salt, I usually get asked this question: Just what is kosher salt, and why do I have it if I don't cook kosher?
How Kosher Salt Is Made
Salt is a naturally occurring substance that is harvested from either seawater or rock-salt deposits in salt mines. To produce salt, the water must be evaporated from seawater or brine made by pumping water into the rock deposits. After the water is gone, the remaining salt crystals can be processed in many different ways and are sometimes treated with anti-caking additives.
Kosher salt is a coarse-grained salt made from the salt crystals. It is usually not iodized, but some brands may contain an anti-caking agent. The evaporation process determines the salt's final shape, so kosher salt can be flat or pyramidal in structure depending on the brand. The top two brands are Morton and Diamond Crystal: Morton's is much coarser than table salt, but Diamond Crystal is even coarser than Morton.
How salt is harvested and made
How Kosher Salt Got Its Name
Any salt can be kosher if it's produced under kosher supervision, but it's not because of Jewish dietary guidelines that kosher salt got its name. In fact, something labeled "kosher salt" can actually not be kosher at all!
Kosher salt's original purpose was really to kosher meat, meaning to remove the blood from meat, so it's really koshering salt. Certain salt companies labeled the boxes of this coarse salt kosher salt rather than koshering salt, and the name stuck.
→ Read more: The Curious History of Kosher Salt
When to Use Kosher Salt
Because kosher salt varies in shape and size across different brands, it doesn't always measure out consistently. (This is why only table salt is used in recipes here on The Kitchn, unless specified differently, since it measures out much more consistently.) In recipes where the kosher salt brand isn't specified, use your judgment if it seems like it's calling for a lot of salt and err on the side of less in the beginning.
The best usage of kosher salt is when you're seasoning food with your hands, especially meat and vegetables before cooking. You can easily pick up pinches with your fingers, and since they don't dissolve immediately, you can visually see where you've sprinkled it and determine if it's even or if you need to do more. I also like to keep kosher salt out on the dinner table since it's easy to pick up a small amount to season my cooked food.
Kosher salt is also great to use when a recipe specifies "coarse salt." However, many bakers tend to shy away from kosher salt and call for table salt instead because they feel that it dissolves more quickly and evenly into baked goods.
Kosher Salt and Substitutions
There are times when a recipe calls for a certain type of salt that you don't have or might have run out of. Since salts can be in such varying shapes, weight is the best determination. However, most recipes don't call for a weight of salt, just volume, and most homes don't have kitchen scales that are capable of weighing out such small amounts anyway.
Experts like Cook's Illustrated have done the weighing and measuring to determine equivalent measurements when using different kinds of salt, and here's what they recommend:
1 teaspoon table salt (fine salt) =
1 1/2 teaspoons Morton kosher salt =
2 teaspoons Diamond Crystal kosher salt