After watching an Ina Garten episode today I was reminded that I have never seen an explanation of the difference between kosher salt and sea salt. Because I signed up for Google's Bard I though it an interesting opportunity to ask the question. This is what I got back

Kosher salt is made from evaporated seawater, while sea salt is made from evaporated ocean water.

What nonsense!

I used the same question at ChatGPT. It did not make that claim. However, it did not explain how kosher salt is made only what its primary purpose is. A supplementary question of "how is kosher salt made" mentions that it is produced by evaporating water from a brine solution. The question would then become what is the difference between brine and sea water and also where does the brine solution come from in the first place but that's for another day.

I think I will stick with using Maldon Sea Salt in my cookery and baking.

According to one web site: "Kosher salt got its name because, historically, it was used for its effectiveness in koshering meat, the Jewish process of preparing meat for consumption. The larger grains draw out moisture from meat faster, which is part of the koshering process". One book that may be worthy of a read: 

Salted: A Manifesto on the World's Most Essential Mineral, with Recipes

For a conversion chart on different types of salt: click here

My mother-in-law was born in the English county of Cheshire and insisted that Cheshire salt was the best. I knew of no brand named "Cheshire". One day I had the experience of being with her in the local supermarket and she picked up what she said was Cheshire salt. It proved to be the cheapest brand on the market. She also over salted everything; boiled potatoes, for example, tasted of nothing but salt. Once food was served up she then proceeded to put exra salt on her food!

Kosher salt has to be unadulterated and quite coarse grained, because fine salt is not used for koshering in the preparation of meat during butchery - it is a subcategory of sea salt, and koshering is the primary purpose

My local Jewish butcher's shop here in London gets huge sacks of Israeli sea salt labelled as "coarse sea salt for koshering" 

The practical difference in cooking is that if you are measuring by volume and not weight there may be quite a difference between spoonfuls of coarse/kosher sea salt, fine sea salt and flake sea salt such as Maldon or Anglesey The taste of equivalent weights of kosher and other sea salts won't be much different - the point in the US is that it's not iodised, as iodised salt is slightly bitter.

In the UK it is harder to find iodised than non-iodised salt, though you may see yellow packets on the shelves

Interesting - in the U.K. I've not come across mined/rock salt for koshering, but then kosher salt is not frequently sold for kitchen use

Of course, rock salt was laid down by the drying up of ancient seas, ultimately it's all sea salt

Should you ever get the chance to visit either the Polish or Austrian underground salt mines, they are rather touristy but totally worth it, fun and informative. There's one in Columbia too which a friend enjoyed. 

So what happens when one recipe calls for sea salt and another calls for kosher salt?

I ignore the kosher salt and substitute sea salt

It's going to depend on the size of the salt grains or flakes if you are measuring by volume so you shouldn't assume a teaspoon of salt gives you the same weight no matter what type. 1 teaspoon is not the same amount of salt if measuring fine sea salt, Morton's kosher, Diamond Crystal kosher or Maldon sea salt. Epicurious has a very handy salt conversion table but unfortunately it is behind a paywall (though you may be able to access it if you haven't uased their site in a while). Using their table and this one I estimate that 3g of salt is equivalent to 1.4 tsp Maldon sea salt, 1 tsp Diamond Crystal kosher, 1/2 + 1/8 tsp Morton's kosher, 1/2 tsp fine sea salt.

The other factor that is considered when comparing other salts is "saltiness". Each salt tastes different, and has a different level of saltiness. I use celtic sea salt almost exclusively, and it is less salty (and more mineralised) than the common brand salts in the supermarket. Even tho the grind can be equal, I have to be careful if cooking elsewhere and using other salts, that I don't over-salt the dish. It's good to taste the salt first (on its own, just a little on your tongue) if it is new to you.

Kosher salt is not a thing here, but we do have Himalayan Salts, local salty river salts, and a range of sea salts available.

Originally Posted by: bittrette

So what happens when one recipe calls for sea salt and another calls for kosher salt?

I use the salt I have, that I am familiar with.  I happen to use Morton's Kosher, because it is easily available.  I have a box of Malden which I save for finishing. I don't keep fine grain salt in the house, having found that I like the larger grained kosher variety-I feel like I have better control.  I suspect that sea salt/kosher salt is the recipe writer using a coarse salt rather than fine. 

Alll that said, I don't bake very often, so all of my salting is to taste.

Zephy

But what do the recipe writers mean by specifying one or the other?

ETA: I don't subscribe to the Condé Nast cooking sites. So the recipes are behind a paywall when I access the site. BUT: The cooking advice pages are not; I can access them just fine.

If you are interested in this topic, see Darcie's new post.

Originally Posted by: bittrette

But what do the recipe writers mean by specifying one or the other?

Each recipe writer will specify the one they usually use and prefer - US cooks are likely to specify kosher salt, as it's commonly used in the USA; UK and European writiers are more likely to have sea salt, as kosher salt is not sold in ordunary grocery stores in most countries,

As long as you don't use iodised table salt, the avoidance of which in cooking is the main reason for specifying kosher salt in countries where table salt is iodised by law, it won't matter

The perceived differences in "saltiness" is mainly observed when tasting a few grains dry or finishing with it, once dissolved there's very little difference, but flakes or fine or coarse crystals dissolve differently in your mouth and that's what you notice.

I use fine crystal sea salt for most things, it costs £1.80 per kg from the zero waste shop, and Sel de Guerande - very coarse grains of slightly grey salt for where I want the crunch or appearance