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Removing Salt


ChefCrash
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... I'd guess the salt ion(s) can penetrate a cell wall much easier than a big old molecule...

Hi, Robert. I'm going to be pedantic and repeat that as I understand it, salt doesn't penetrate cell walls - it's too big, even dissolved in water. It does dissolve in water, unlike flavours in the form of fatty or oily molecules.

I think your observation about brining and other flavours is a good one - I too notice that my bacon absorbs far less herbal / pepper flavour in proportion to the amount in the brine, compared to salt absorption. I can sure believe in salt penetrating the small fissures in the food fibres (between cells / between cell bundles) more easily.

QUIET!  People are trying to pontificate.

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... I'd guess the salt ion(s) can penetrate a cell wall much easier than a big old molecule...

Hi, Robert. I'm going to be pedantic and repeat that as I understand it, salt doesn't penetrate cell walls - it's too big, even dissolved in water.

From McGee's On Food and Cooking (p. 283, new edition): "Table salt in neutral cooking water speeds vegetable softening, apparently because its sodium ions displace the calcium ions that cross-link and anchor the cement molecules in the fruit and vegetable cell walls, thus breaking the cross-links and helping to dissolve the hemicelluloses."

Sounds to me like salt can penetrate cell walls, or at least its sodium ions can.

(Incidentally, this ability of salt to soften vegetables during cooking is the reason the outside of a potato cooked in salted water can start to dissolve before the center is done.)

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Right: sodium ions do in fact penetrate cell walls. See here for some of the painful details. In fact, based on my reading of that page (though I warn you I am not a biologist and aerospace engineers are not noted for their understanding of biology!), it seems that it could help to explain why sodium in particular seems to make its way through cellular material (e.g. food) much faster than other substances.

Chris Hennes
Director of Operations
chennes@egullet.org

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You guys are forgetting something even if the potato thing were true chemically. Let's say you have a liter of water that's salted at 4% and you want to bring it down to 3%. That means you need to remove 10g of salt. Assuming there's no magic process that can make potatoes more salty than the ambient water, for potatoes to be at a 3% saltiness with 10 grams of salt would require 333 grams of potatoes.

In other words, One or two slices aint gonna cut it. You would have to add 1/3rd your quantity of soup in potatoes to fix a mild oversalting. If the effect exists, however it's occurring, it's not because the potatoes are sucking in salt in prodigious quantities. Perhaps the starch is making it taste apparently less salty, perhaps it's a pure placebo effect. But the math doesn't work out for it to be removing the actual salt ions.

PS: I am a guy.

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You guys are forgetting something even if the potato thing were true chemically. Let's say you have a liter of water that's salted at 4% and you want to bring it down to 3%. That means you need to remove 10g of salt. Assuming there's no magic process that can make potatoes more salty than the ambient water, for potatoes to be at a 3% saltiness with 10 grams of salt would require 333 grams of potatoes.

In other words, One or two slices aint gonna cut it. You would have to add 1/3rd your quantity of soup in potatoes to fix a mild oversalting. If the effect exists, however it's occurring, it's not because the potatoes are sucking in salt in prodigious quantities. Perhaps the starch is making it taste apparently less salty, perhaps it's a pure placebo effect. But the math doesn't work out for it to be removing the actual salt ions.

+1 on this..its the same "equilibrium"(sp).. concept used in brining,,, to end up with a specific finished salt % in a brined product...

Bud

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Maybe salt taste is masked by starch, maybe. If so how to prove or disprove?

The nice part of using whole potatoes or chunks is you can remove them at some point and do a salinity check. I don't know if you can [at a consumer level] buy potato starch. I would use instant mashed potatoes as we all know they would contribute no taste but I don't know if we could remove them from the mix.

Would one then simply taste test coupled with a salinity check. I think I don't know either enough about the products or the chemistry. Maybe I should have paid a bit more attention to that last chem class back in '72.

What if we found that the starch did mask salt? The math Shalmanase mentioned above would not matter in most cases. [Yeah, I know there must be places where excess salt does something like affect texture but those are not as frequent an occurrence as too salty tasting.]

qrn's comment on +1... I don't understand. Yes if a chunk of food is left in a brine, it will reach equilibrium. That was discussed above when talking about canned goods. so I'm missing what you mean.

Edited by RobertCollins (log)

Robert

Seattle

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I don't think the mechanism that McGee describes, where sodium ions are swapping with calcium ions in the potato, can be responsible in itself for the absorption of much salt, since the amount of calcium in a medium 299g potato is on the order of 41mg ( http://www.nutritiondata.com/facts/vegetables-and-vegetable-products/2770/2 ). The molar mass of calcium is 40.80 g/mol, and for sodium it's 23.00 g/mol, and the replacement of calcium with sodium isn't going to be complete, I don't think, without the potato falling apart, but even if it were, that means that by this mechanism alone, a medium potato could only remove around 25 mg of sodium from whatever solution it's in, and there are about 2300 mg of sodium in a teaspoon of salt.

So that mechanism aside, there are many articles on the net about what happens to a potato in (cold or room temperature) salt water, because this is a fairly basic demonstration for teaching about osmosis in high school biology classes, and what happens is that the fluid inside the potato cells does tend toward equilibrium with the solution it's immersed in, but the salt draws water out of the potato; the potato doesn't draw salt into its cells. So if this is what is happening, then the potato is just making the soup more watery.

Another possibility might be that if the salt and heat are breaking down the potato cells, then maybe there's something else going on after the cell membranes are damaged enabling the potato to absorb salt, but it could be that this just allows the potato to release even more water.

Edited by David A. Goldfarb (log)
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Robert, this is what I was speaking of,,,

If you add 1/2 pound of salt to 1 pound of water you have a solution that is 50% salt. If you then put a pound of meat (or potatoes) in it, and let it sit until all of it reaches equalibrium, the meat/watercombination will have 1/2 pound of salt to two pounds of meat/ water,,,, or 25%,,, the meat and the water will be equal in % of salt.(ie 25%)...Thus the salt level in the liquid will have dropped from 50% to 25%

I use this concept when I want an exact %percentage of salt in my brined products...(I made an Excel spread sheet to be able to easily calculate this effect...)

Bud

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