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Removing Salt


ChefCrash
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This has been discussed in at least two threads, here and now here. Some claim it works, others don't agree, some claim potatoes don't even absorb salt.

Into a 2 qt. pan I measured 1 Liter (1 Kilo) of tap water. In that, I dissolved 118 grams of canning salt. Why 118 grams/liter? It's a solution I often use for pickling and knew it's specific gravity using my hydrometer.

Water weight = 1000g

Pot weight = 534g

Salt weight = 118g

Total = 1652g

Potato weight= 446g

Total = 2098g

Hydrometer read 18.5 *brix (Bx)

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I quartered 446g potatoes

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Added them to the water. The soup was brought to a boil then simmered slowly for 30 minutes.

I made sure the potatoes were as tender as possible yet firm enough to rescue from the pot without falling apart.

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Before removing the potatoes the pot was weighed. So far 296g were lost to evaporation.

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The potatoes were drained and weighed. They lost 14g. We don't care where they went, more importantly they didn't absorb water as this person claims.

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I should have immediately weighed the pan without the potatoes, but wanted the solution to cool to 85*F before taking a S.G. reading. My wife and I used the time to conduct a taste test (more on that later). Twenty minutes had elapsed. Evaporation as well as water lost in the screen of the strainer (even though I tried hard) might explain why I lost 48g (above and beyond) in this photo.

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Enough fresh water (212g) was added to the soup to replace lost water and sampled in the hydrometer.(here I made a big mistake, see who can spot it). The reading is 15*Bx.

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What does it all mean?

Well, if a one liter solution containing 118g = 17.7 tsp salt registers 18.5* Bx, then a solution registering 15* Bx contains 14.35 tsp salt. A difference of 3.35 tsp or 22.3g salt.

Where did the salt go?

The taste test

I took 2 of the largest pieces of potato. Ones that were not pocked for doneness. I used a sharp knife to reach the core. The outer layers were inedible. The core tasted a little salty for my wife and just salty enough for me.

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Conclusion?

First let me address the mistake mentioned above. When I replenished the solution with fresh water, I added 212g of water based on a total pot weight of 1534g which was pot+water. The actual total weight should have been: pot+water+salt=1652g. So, an additional 118g of water should have been added to reconstitute the soup.

I needed to add 330g of fresh water to bring the total weigh back to a kilo. Calculations prove that a total of over 3 tsp of salt were removed by the potatoes.

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This is a very interesting experiment. Thank you for conducting it.

But does it definitively answer the question? Probably not.

You stated in your description that the potatos lost 14g and that you don't care where this went. This may be something you do need to care about.

There is likely to be a weight gain in the potatos from the water and the salt. The weight loss is likely to have represented a transfer of potato starch to the water. If you were to evaporate the water, this would show up as a deposit similar to potato starch you can purchase. This throws a problem in the way of brix measurement as there are a number of scientific papers from the food technology literature that talk about the interaction between salt and potato starch and its effect on specific gravity (and therefore brix measurements).

It is possible therefore that the result is an artefact of the procedure.

You did a taste test on the potatos and determined that they were salty; how about a taste test on the water itself? Would it taste less salty than a solution that had an equivalent amount of potato starch added to it? (you need to do this to counter the interaction between the potato starch and the salt on taste) For completeness, these tests should be conducted as a double blind (neither the person giving the taster the sample nor the taster knows which sample is which).

This is an important question that deserves research such as that which you have undertaken. It also needs a few clarifying tests to make sure that the conclusions are correct.

Nick Reynolds, aka "nickrey"

"The Internet is full of false information." Plato
My eG Foodblog

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I don't think you made a mistake. You used specific gravity (m/V) to measure the concentration of salt in the water. Bringing the water to the original weight (volume) allowed you to compare the final concentration to the original. Had you added enough to compensate for the salt would have diluted the final reading since you would have a greater volume.

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Great experiment, ChefCrash. And like all great experiments, one that leads to more questions. As nickrey points out, the potato starch issue is one. What other methods are available for measuring salinity? I have no experience in the field, but maybe some saltwater aquarium people would know. Are there test kits available at aquarium stores?

I would certainly expect the potatoes to absorb salt simply on the basis of a system's tendency to equalize concentrations: the potatoes go in with a near-zero salinity, and the system is going to act to increase that salinity and decrease the salinity in the water until an equilibrium is reached. In that sense adding potatoes is no different than adding and then removing an equivalent quantity of water. Or chicken. Or whatever. Is there any compelling reason to believe there is some special property of the potato that would somehow increase its ability to absorb salt, above and beyond any other substance?

Chris Hennes
Director of Operations
chennes@egullet.org

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For my own knowledge, I just did an entirely different kind of experiment, to see what would happen in something closer to "real life." That is, I was interested in a liquid closer to what I'd consider "oversalted" soup, instead of a brine. So I dissolved a tablespoon of Diamond Crystal kosher salt into a quart of water and heated it to a simmer. I removed half a cup of the liquid, then added a potato (russet, peeled and sliced about an inch thick). I covered the pan and continued to simmer for 15 minutes, then double strained the liquid and measured out another half cup. I heated up the initial sample so the two liquids were the same temperature and then -- surprise! -- tasted them. I could taste a faint hint of potato in the second sample, but the salt level was no different.

Yes, I know this was hardly a controlled experiment. There may have been a slight bit of evaporation, although the lid was tight fitting, and I didn't seen any steam escape. I knew which sample was which, and I didn't try to test the salinity level in any objective sense. I just tasted them.

But to me, that's what's important if this is supposed to be a real life method of saving oversalted liquids. The second one didn't taste less salty. It was a just a waste of a potato and 20 minutes.

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The standard for measuring salinity is total dissolved solids (evaporating the liquid and measuring the residue). Conductivity, which is what Wolke used, is typical in process applications. I've never heard of using specific gravity to measure salt concentration (until now).

But to me, that's what's important if this is supposed to be a real life method of saving oversalted liquids. The second one didn't taste less salty. It was a just a waste of a potato and 20 minutes.

Right. It's not about the potatoes. It's about the soup.

Dave Scantland
Executive director
dscantland@eGstaff.org
eG Ethics signatory

Eat more chicken skin.

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Hi

Let me first say that what led me to do this had more to do with people's claims (including some TV personalities), that potatoes don't absorb salt, or benefit from being boiled in salted water, than whether they can be used to correct a mistake.

I was trying to hit two birds with one stone.

So far, can we all agree that potatoes do absorb salt., and that potatoes don't act as sponges as Wolke suggests?

Let me answer some questions

The standard for measuring salinity is total dissolved solids (evaporating the liquid and measuring the residue). Conductivity, which is what Wolke used, is typical in process applications. I've never heard of using specific gravity to measure salt concentration (until now).

Before electricity my ancestors only had a Hydrometer to check salinity of brines, it was in the form of a floating egg.

...

I would certainly expect the potatoes to absorb salt simply on the basis of a system's tendency to equalize concentrations: the potatoes go in with a near-zero salinity, and the system is going to act to increase that salinity and decrease the salinity in the water until an equilibrium is reached. In that sense adding potatoes is no different than adding and then removing an equivalent quantity of water. Or chicken. Or whatever. Is there any compelling reason to believe there is some special property of the potato that would somehow increase its ability to absorb salt, above and beyond any other substance?

I agree, potatoes don't posses special qualities. Just that they're relatively inexpensive and usually are at hand and minimally alter the taste of whatever one is trying to rescue.

...

You did a taste test on the potatos and determined that they were salty; how about a taste test on the water itself? Would it taste less salty than a solution that had an equivalent amount of potato starch added to it? (you need to do this to counter the interaction between the potato starch and the salt on taste) For completeness, these tests should be conducted as a double blind (neither the person giving the taster the sample nor the taster knows which sample is which).

Obviously, the salt removed from this exaggerated salt to water ratio was not going to have a discernible difference to me.

Now a question for Nick and Chris, what are the effects of starch interactions with salt in a solution?

Are we talking about the fact that starch has a S.G. of half that of water (0.6), and that it's release into the solution causes it to further dilute it giving us erroneous results?

If so, I repeated the experiment. This time the way Jaz did (with a little more control).

I will post results tonight. Gotta go to work.

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I realize that y'all whippersnappers are in the middle of a scientific exploration here, but I can't help but offer some empirical evidence gathered from five+ decades of cooking.

Adding potatoes to an over-salted liquid has rescued various soups and stews and pasta sauces, etc., for my family many times.

And I'm talking about everything from minor flubs such as my own inattention and lapses in concentration, to catastrophes on the order of "Mommy, I helped put in more salt" and the time that the top flew off of the salt shaker and into the soup only a few hours before dinner guests arrived.

It absolutely works.

And as for "wasting potatoes"...

No, you don't have to "waste" those potatoes. There are lots of things you can do with them. Cook them the next day. As a vegetable, or an addition to another soup, or sliced and fried up in your skillet.

It's not magic. It's just that potatoes do require a lot of salt - as anyone can tell you that's ever "corrected the seasonings" (as Julia used to say) but then notices, right before serving, that after the potatoes were added, the dish is now nowhere nearly salty enough.

______________

Edited by Jaymes (log)

I don't understand why rappers have to hunch over while they stomp around the stage hollering.  It hurts my back to watch them. On the other hand, I've been thinking that perhaps I should start a rap group here at the Old Folks' Home.  Most of us already walk like that.

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  • 2 weeks later...

What no answers?

The article from which the following quotes were obtained

Of course, I also simmered the same amounts of the two liquids in the same covered pot on the same burner, because scientists, as you must be thinking by now, are absolute nuts about controlling all conceivable (and even some inconceivable) variables, except the one they're trying to compare. Otherwise, you'd never know what caused any differences you might observe. I could very easily sermonize here against those who try something once under completely uncontrolled circumstances and then go running around saying, "I tried it and it works." But that's another column.
Sure enough, the potato simmered in plain water was bland, the potato simmered in the one-teaspoon-per-quart water was salty, and the potato simmered in the one-tablespoon-per-quart water was much saltier. But does this mean that the potato really removed salt from the "soups?"

No. All it means is that the potatoes soaked up some salt water; they didn't selectively extract salt out of the water. Would you be surprised if a sponge placed in salt water came out tasting salty?

Second, if in spite of the tight cover and gentle simmering, any substantial amount of water had been lost from the pots by evaporation while cooking the potatoes, the conductivity of the water would have gone up, not down, and no such effect was found after correcting for the conductivity provided by the potato itself.

This dude assumes potatoes are like sponges. Which explains why he didn't bother tell us the ratio of potato to water he used. Understandable, since sponges or "six, 1/4" slices of potato totaling 300 square centimeters of surface area", (which amount to a cylinder slightly larger than a silver dollar, 1.5" long), dipped into a saline solution, only remove "suck", part of the solution leaving the remainder with the same salinity/conductivity.

But what if the sponge is 80% water saturated before it's dipped in the salted water?

Potatoes are 80% water!

He's not sure if he had evaporation? I don't understand the last paragraph at all.

I think I've got an airtight case, don't you? Nobel Committee, please note.

I hope he's not holding his breath. :smile:

My results tomorrow.

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I concur strongly with you, Jaymes. My experience matches yours: potatoes need to be cooked in salt water, and/or need plenty of salt. I've used them successfully to absorb salt to rescue soups & stews. I haven't personally come across celebs denying all this - I wonder about anyone who'd make such a claim. Are they all mouth and no kitchen ?

An over-salty potato can even be put aside and combined with less salted ones cooked later, in mash, say.

I'll also note that osmotic pressure (which acts across cell walls in the spud) means the movement of water from the less-salty side to the more-salty side. Salt doesn't pass through cell walls. So one might expect dehydration of potato cells in salty water (so maybe 14g is starch and water).

Salt itself of course migrates into the potato in the gaps between cells / larger fissures in the potato's flesh, as it does into other foods during brining / pickling / salting.

QUIET!  People are trying to pontificate.

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Do a freeze test. Freeze a non potato saline solution next to an equal amount of potato boiled (and then removed) solution. If you've removed as much salt as you say you have, you should be able to get a considerably firmer freeze.

Potato starch does the lower freezing point, but it should be negligible compared to the freezing point lowering capabilities of the salt.

OR

Put this argument completely to rest and shell out for one of these:

http://www.acornnaturalists.com/store/SALINITY-TEST-KIT-P450C108.aspx

Edited by scott123 (log)
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It seems to me that the question is not "does adding potatoes to soup decrease saltiness" since I agree with Jaymes and Blether that it clearly does: to me the real question is, "does adding potatoes decrease the saltiness MORE than adding any other non-salty item." For example, if you add water to your soup, you will decrease the salinity. Is adding a potato any different? Does salt have a tendency to accumulate in a potato? It seems to me that all you are doing when you add a potato is effectively diluting your soup. If you then proceed to remove the potato, of course the salinity will have decreased, in the same way that if you added water, stirred it up, and then removed that amount of liquid would result in decreased salinity.

Chris Hennes
Director of Operations
chennes@egullet.org

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It seems to me that the question is not "does adding potatoes to soup decrease saltiness" since I agree with Jaymes and Blether that it clearly does: to me the real question is, "does adding potatoes decrease the saltiness MORE than adding any other non-salty item." For example, if you add water to your soup, you will decrease the salinity. Is adding a potato any different? Does salt have a tendency to accumulate in a potato? It seems to me that all you are doing when you add a potato is effectively diluting your soup. If you then proceed to remove the potato, of course the salinity will have decreased, in the same way that if you added water, stirred it up, and then removed that amount of liquid would result in decreased salinity.

Well, in my experience, adding water dilutes the soup of all of its flavor. It makes it, um, 'watery.' That's nothing like adding a potato or two which doesn't, by my definition anyway, "dilute" the soup at all. It just sucks up the salt. I agree that anything that requires a lot of salt would probably do the same thing. But I think pulling out two or four potato halves is a lot easier than pulling out, for example, 50 pasta noodles, noodle by noodle.

I don't understand why rappers have to hunch over while they stomp around the stage hollering.  It hurts my back to watch them. On the other hand, I've been thinking that perhaps I should start a rap group here at the Old Folks' Home.  Most of us already walk like that.

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Several discussions going on here, as it relates to correcting salt levels in an oversalted soup, potatoes might work. I am not sure since I've never had to try it. Well, maybe I did once in a pot of beans and I think it worked, but that was a long time ago.

Do they suck water like sponges as Wolke suggests? I'm firmly with ChefCrash here. Hell no. Wolke is nuts. It's sort of like the argument that mushrooms cannot be washed because they are "sponges". Again bullcrap. Alton Brown weighed mushrooms, soaked them in water and re-weighed them. 2 lbs gained maybe a couple of grams. Probably due to a couple of tablespoons stuck in some of the caps.

Back to the potato, It makes perfect sense to cook potatoes in salted water. They do come out tasty and salted, but not watery. Even if you cook the heck out of them, like Heston Blumenthal does for his fried potatoes, once you remove them from water, they are not soaking wet and drenched in water.

Chris, why would you say that adding the potato is diluting the soup? Due to the starch it adds? How is it like adding water? If you add water, the stock is diluted and then when you remove the exact same volume of liquid, you are not just removing the water you added, you are removing diluted stock. The potatoes are not soaking much stock if any and can easily be removed.

E. Nassar
Houston, TX

My Blog
contact: enassar(AT)gmail(DOT)com

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...if you add water to your soup, you will decrease the salinity. Is adding a potato any different? ...

Well, in my experience, adding water dilutes the soup of all of its flavor. It makes it, um, 'watery.' That's nothing like adding a potato or two which doesn't, by my definition anyway, "dilute" the soup at all. It just sucks up the salt.

Once again, yes (Sorry, Chris). That's the whole point about potato-adding, isn't it ? Because trying to adjust using water ruins the dish.

QUIET!  People are trying to pontificate.

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That's really what I'm trying to get at here: how is it that potatoes can absorb excess salt, but don't absorb the other flavors? If you put in a potato, let it absorb salt, then take it out, how is it that the potato is not also absorbing other desirable flavors?

Chris Hennes
Director of Operations
chennes@egullet.org

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The potato pretty obviously does absorb some of the other flavors. Peppers, herbs, spices, but I don't think it absorbs as much of them as it does the salt. And it doesn't seem to grab up as much in the way of juices. If I am making a chicken soup, for example, and I get it too salty and put in a potato or two, you can definitely taste in the potato some of the other seasonings I've put into the soup, but the broth after I take the potatoes out still seems plenty "chickeny" for want of a better word. I can add a pinch more oregano and paprika, etc., if the broth seems to need it. But the overall flavor of the soup doesn't seem diluted to me like it would be if I had added more water. The broth is still as thick and rich as it was when I put in the potato. It wouldn't be had I added water.

I don't understand why rappers have to hunch over while they stomp around the stage hollering.  It hurts my back to watch them. On the other hand, I've been thinking that perhaps I should start a rap group here at the Old Folks' Home.  Most of us already walk like that.

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Which is completely fascinating! Why is a potato preferentially absorbing salt, but not other flavor molecules? Is it that those molecules are too large to penetrate the potato quickly and would eventually be absorbed, but you take the potatoes out before that happens? And is it unique to the potato, or to starches (pasta, etc.)?

Chris Hennes
Director of Operations
chennes@egullet.org

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I have an old cook book (ca. 1911) that advises "when the soup-stock has been reduced and on tasting is found to be excessively salty, remove from the grate, tie half a loaf of white bread, stale but not hard, tightly into a pudding muslin and submerse fully into the soup-stock, using a weight, if necessary and allow to cool until tepid. Remove the muslin and allow to drain but do not force. Replace the liquid taken up by the bread with clear water."

I've never tried this personally but wonder if the absorption of salt by the bread would be similar to that of a raw potato.

I am reminded that when dumplings are prepared when intended for cooking in soup, they are made with less salt than when intended to be cooked in water. They definitely do pick up salt from the soup, it is easy to taste.

P.S. There is no mention of the size of the loaf of bread but I would guess it would be a 1-pound loaf, which I think was standard at that time.

Edited by andiesenji (log)

"There are, it has been said, two types of people in the world. There are those who say: this glass is half full. And then there are those who say: this glass is half empty. The world belongs, however, to those who can look at the glass and say: What's up with this glass? Excuse me? Excuse me? This is my glass? I don't think so. My glass was full! And it was a bigger glass!" Terry Pratchett

 

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I have an old cook book (ca. 1911) that advises "when the soup-stock has been reduced and on tasting is found to be excessively salty, remove from the grate, tie half a loaf of white bread, stale but not hard, tightly into a pudding muslin and submerse fully into the soup-stock, using a weight, if necessary and allow to cool until tepid. Remove the muslin and allow to drain but do not force. Replace the liquid taken up by the bread with clear water."

Seems to me that all one is doing here is taking out some liquid that's too salty and replacing it with water. Why use a loaf of bread instead of a ladle?

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I have an old cook book (ca. 1911) that advises "when the soup-stock has been reduced and on tasting is found to be excessively salty, remove from the grate, tie half a loaf of white bread, stale but not hard, tightly into a pudding muslin and submerse fully into the soup-stock, using a weight, if necessary and allow to cool until tepid. Remove the muslin and allow to drain but do not force. Replace the liquid taken up by the bread with clear water."

Seems to me that all one is doing here is taking out some liquid that's too salty and replacing it with water. Why use a loaf of bread instead of a ladle?

And let a perfectly useful pudding muslin go to waste?

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I wonder but sure do not know how the starch mentioned repeatedly above, plays out with the potato or the bread. Does the starch act like some kind of catalyst?

As to why the potato doesn't take out more of the other spicing and herbs, I've noticed that when brining; the herbs really do not flavor the brined item in any relationship to the salting effect. Not being a chemist, I'd guess the salt ion(s) can penetrate a cell wall much easier than a big old molecule from a infused herb.

Again I am only guessing. edit: 'cause I am not a very good speller either

Edited by RobertCollins (log)

Robert

Seattle

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