Kosher vs. Sea Salt

Sea salt usually has a significant amount of impurities, enough to taste in some recipes. It also costs more than what many chefs consider the standard, Diamond Crystal Kosher, which is cheap and neutral in flavor.

If the recipe gives you the weight to use and you own a kitchen scale (you should), you're good to go. Otherwise the problem is determining the amount to use as every sea salt and every kosher salt has a different size crystal and therefore a different weight for any given volume. You can try substituting one for one and make adjustments from there.

you can substitute the salt, if you are weighing out the amounts. If you are doing it by volume, you may need less sea salt since kosher salt is 'fluffier' than the more dense sea salt. If you do a 1:1 substitution with the sea salt, the ratio of cure will be saltier and gravlax may be more salty than intended.