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Several of my recipe books call for baking potatoes on a layer of (rock) salt, e.g. I'm currently following one for gnocchi that has this very instruction.

Searching yields many recipes, but I can't really find the "why" of it, nor what it technically accomplishes. Our own cooking.se site yields no relevant results either.

I can't quite imagine either what it would accomplish, except for perhaps salt the potatoes a bit; but that seems rather inefficient (why not add some salt later to the gnocchi dough?). Or perhaps it's meant to draw all fluids?

Why would you bake potatoes on a layer of (rock) salt? What does that do to the potatoes?

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This is what America's Test Kitchen (sorry, paywalled) has to say about it:

Sometimes baked potatoes can use a flavor boost. And instead of light and fluffy, most often they are dense and crumbly. We found that baking the potatoes on a bed of salt remedied these problems. Moisture that escaped the potatoes during baking was trapped in the enclosed pan, absorbed by the salt, and eventually reabsorbed by the potatoes, making their skins tender and their flesh light and fluffy. All we needed to do was fine-tune the variables. Using a hot oven and uncovering the potatoes toward the end of cooking ensured dry, crisp skin. A 13 by 9-inch baking dish provided plenty of space so that we didn’t have to crowd the potatoes, and 2 1/2 cups of salt allowed us to thoroughly cover the bottom of the pan.

I have found that salt roasting potatoes makes the skin crispy, without it getting hard. Like the above says, the potato itself seems fluffier. The way the salt seasons the potato is particularly nice as well. Incidentally, you can reuse the salt over and over again, so it's not as wasteful as it might seem when you first consider the method. You'll want to keep separate salt for things like this, though, since it picks up potato flakes and discolors a bit.

EDIT The ATK method calls for covering the 9X13 baking dish (for 4 potatoes and 2 1/2 cups of salt) tightly with aluminum foil and roasting at 450F (232C) for 1 1/4 hours. Remove foil, brush potatoes with oil, raise oven temp to 500F (260C) and continue roasting for 10-20 minutes, until potatoes are tender when pierced with a knife and the skins are glossy.

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    How does this differ from coating the potato in salt prior to baking it?
    – Michael McGriff
    Dec 10, 2014 at 17:32
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    @MichaelMcGriff It doesn't differ if you coat with a lot of salt. It takes a lot of salt to pull out the moisture from the potatoes, a heavy sprinkle won't do it.
    – Jolenealaska ♦
    Dec 10, 2014 at 17:45
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    The potatoes cooked using the method described are clearly moist because they're covered for most of the cooking, not because of the salt. The idea that the salt is simultaneously able to draw water out of the potatoes and feed it back in has no basis in reality. People say the method is a good one, so I don't doubt that, but the explanation offered for why it works is total hocus pocus.
    – David Richerby
    Dec 11, 2014 at 12:10
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    @DavidRicherby Also, this is ATK. I guarantee you that if they tried roasting covered with salt, they also tried roasting covered without salt. It's quite possible their explanation is wrong, but when they say it "remedied these problems" they mean it.
    – Cascabel ♦
    Dec 11, 2014 at 15:47
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    @DavidRicherby If you read my answer carefully, you can probably tell that I'm not particularly enamored of ATK's explanation of the science of "why" salt-roasted is better. But, I completely agree with Jefromi. This is ATK. The method is great and it makes a superior potato; my own experience backs that up. Perhaps next season they'll give us a better explanation as to "why".
    – Jolenealaska ♦
    Jan 17, 2015 at 11:26
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There are many roasting recipes that use a bed or even a dome of salt.

This has three effects that I am aware of-

1- It salts the food obviously. This isn't necessarily a reason all by itself. As you noticed salt is just as easily added later.

2- It keeps the food off the pan. In the case of fish this can make for easier service.

3- The salt becomes part of the cooking medium. It stores and releases the heat of the oven producing slower and more even heating. This is the primary reason recipes call for roasting on salt.

Unless your oven is guilty of gross thermal irregularities, I am skeptical that baking potatoes on salt will make much of a difference at all. It might might make for an interesting presentation at the table.

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    Sounds like it could be a good compliment to the "dig a hole and fill it with hot rocks from the bonfire and bury stuff in it for 12 hours" cooking technique
    – shadowtalker
    Dec 11, 2014 at 16:54
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So here's something I learned in high school that could be of some value. If you have two densities of something separated by something that allows water to flow through, like the skin on your potato, it will try to reach an equilibrium. So in this case you have two different areas with different salt densities. In the potato there is likely little sodium, so water will flow into the potato (with the salt) to try to reach equilibrium. Google semi permeable membranes if you want a more in depth explanation.

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  • Hi Russ, this doesn't make much sense. First, the potato skin is not a semipermeable membrane. Each cell wall is, but the skin itself is made out of multiple cell layers. Second, you are saying "water will flow into the potato (with the salt)" - if there is any movement, 1) salt will not flow anywhere, and 2) water will flow out of the potato, not into it, because that's where the high salt concentration is. So one would expect some drying out of the potato, but it is unclear how noticeable the effect would be, when compared to the drying due to evaporation in the hot oven.
    – rumtscho ♦
    Dec 21, 2018 at 12:09
  • You would need sufficient water or other liquid for osmosis. In my experience, the salt ends up forming a hard crust as the moisture comes out of the potato, even if you cover it like in the ATK recipe
    – Joe
    Dec 21, 2018 at 16:54
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In the first Master Class of the 1st season of Master Chef Australia, they made a baked potato--baked on a bed of coarse salt. The reason for this, as explained by one of the Head Chef/Judges, was in so that as the potato cooked (I'm assuming here they baked it unwrapped, since it was was previously done), and released moisture, the moisture would have somewhere to go--into the salt--and you don't end up with a potato with a wet spot on the bottom.

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Just my 2 cents: The salt does not create a salty taste at all to the potato. The salt is used to create a type of a dutch oven and cooks a fluffy inside and a crispy skin. Potatoes are cooked like this at Red Lobster. At one time this recipe was called "The Worlds Best Baked Potato" before the internet. If I remember right the temp you cook at is a little higher then 400, maybe 410 degrees or 425 for 1 hour and 15 minutes or something like that.

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