Cooking With Rock Salt: Food-Grade Only, Plus Ice Cream Makers and Salt Crusts

A lot of the coarse “rock salt” in American stores was never meant to be eaten. It’s sold for ice cream makers or melting ice, and Morton says flat out that its Ice Cream Salt isn’t intended for consumption.¹ So rule one is knowing which kind you’ve got. Food-grade rock salt, simply salt mined from underground deposits, cooks like any other coarse salt. In the kitchen it does three jobs: chilling an ice cream maker, building a salt crust around a whole fish, and seasoning.

Quick guide

Food-grade or not

Under the Codex Alimentarius standard, food-grade salt has to be at least 97% sodium chloride on a dry basis, whether it comes from the sea, rock deposits or natural brine.⁵ America’s Test Kitchen says the same from the cook’s side: salt is sodium chloride wherever it comes from.⁶ Plenty of ordinary table salt starts out as mined salt. The American Heart Association describes table salt as mined from salt deposits and processed to a fine texture.⁷

Morton describes its Ice Cream Salt as large rock salt crystals for gradual cooling in ice cream makers, lists melting ice and snow among its uses, and says it’s not intended for consumption.¹ Only put rock salt in food when the package says food grade or edible, or carries a Nutrition Facts panel. A bag sold for ice cream makers, water softeners or de-icing stays out of the food. That’s a labeling rule. It doesn’t mean such salt is harmful; we just found no regulator data on what non-food rock salt contains.

Rock salt in an ice cream maker

In a hand-crank or bucket-style freezer, rock salt goes in the ice packed around the canister, never in the mix. Nebraska Extension’s coffee-can ice cream instructions pack crushed ice around the inner can, then pour “at least 3/4 cup of rock salt evenly over the ice,” and repack with ice and salt partway through. Don’t overdo it, though. Too much salt freezes the mix too fast and gives the ice cream a poor texture. And don’t let any ice or ice water get into the inner can.²

Salt-crusted fish and meat

For salt-crust cooking, you pack a whole fish or roast in a shell of moistened salt before it goes into the oven. Thomas Keller’s recipe from Ad Hoc at Home is a well-documented version:³

Keller says the method gives very moist fish that’s seasoned but “not at all salty.”³ His recipe uses kosher salt.

Ratio (Method): Food-grade coarse rock salt can stand in by volume for the crust, since you lift the crust off and don’t eat it. We found no test of that swap, so expect the crust to pack a little differently.

On doneness, Keller’s target and the federal guidance don’t match. FoodSafety.gov gives 145°F for fish, or cooking until the flesh is no longer translucent and separates easily with a fork.⁸ Keller’s 125°F is below that. If you’re going by the federal guidance, cook longer or check that the flesh flakes. The same chart gives 145°F with a 3-minute rest for beef, pork and lamb roasts.⁸

Seasoning with food-grade rock salt

Coarse food-grade rock salt works in a salt grinder, in pasta water and in spice rubs. Those are everyday uses, not tested claims. Big crystals pack loosely, so a spoonful holds less salt than a spoonful of table salt. We found no published grams-per-teaspoon figure for coarse rock salt, so salt to taste or weigh it.

As a finishing salt, whole crystals are hard and slow to dissolve. You’ll read that coarse salt sits on the surface without drawing moisture out of food, but we found no test of that, so we won’t claim it. For a crunchy finish, flaky sea salts are the more usual pick; see cooking with sea salt.

Not for pickling

The National Center for Home Food Preservation recommends canning or pickling salt for pickles. It also advises against flake salt because its density varies.⁴ Coarse rock salt isn’t the tested choice; see pickling salt.

Sodium

Rock salt isn’t a lower-sodium salt. Table salt, kosher salt and most sea salts are about 40% sodium, and mined salt is the same compound.⁷⁵ The WHO recommends adults keep sodium below 2,000 mg a day and names raised blood pressure as the main health effect of eating too much; the FDA’s Daily Value is less than 2,300 mg.⁹¹⁰

What isn’t known

• What non-food rock salt (ice cream, de-icing, water-softener grades) contains. We found no regulator data.
• A grams-per-teaspoon figure for coarse food-grade rock salt.
• A published ice-to-salt ratio for ice cream freezers beyond the extension minimums.
• Any test of the claim that cooking meat on a bed of rock salt keeps it juicier.

Related

• Rock salt, the full profile, and rock salt substitutes
• Rock salt vs. sea salt and rock salt vs. table salt
• Himalayan salt, a food-grade rock salt, and cooking with Himalayan salt
• Kosher salt, table salt and too much salt?