4

votes

Does soaking kidneys remove all the nutrients?

Answered on August 19, 2014
Created April 10, 2012 at 2:56 PM

As any-one who's tried to cook them will know, kidneys smell pretty awful. In deference to the preferences of my fiance, I've tried to reduce the urine smell by soaking them (as lots of recipes recommend) and then discarding the liquid before cooking. This works pretty effectively to remove the smell, but I wonder, am I also discarding most of the nutrients (which is, tbh, the only reason to cook the kidneys in the first place?

I've not seen any studies on this, unsurprisingly, but wonder if any-one has any insight?

E35e3d76547b18096a59c90029e7e107

(15613)

on June 21, 2012
at 09:46 PM

I've started giving my liver a bit of a wash, but not felt the need for soaking it- the taste of liver seems OK for me and there's not a smell like with kidneys.

E35e3d76547b18096a59c90029e7e107

(15613)

on June 21, 2012
at 08:48 AM

Thanks Astar. I wasn't aware that kidneys contained much A, D, E. The point about chelating is interesting, hope it's right. I soak them overnight/a day, repeatedly changing the water. That's necessary to remove the smell (and there's still red stuff leaking by the end). Do you know of any reason to think that I'm not pouring off the relevant proteins during this process?

E35e3d76547b18096a59c90029e7e107

(15613)

on June 21, 2012
at 08:43 AM

Also, I'm not thinking of uric acid as a nutrient or worried about its loss. Is there actually any solution that I could practically use that would guarantee the loss of the smell *and* the maintenance of all the nutrients? Cos I just use water, which is probably not 'isotonic to the cells of the kidneys'...

E35e3d76547b18096a59c90029e7e107

(15613)

on June 21, 2012
at 08:41 AM

... And given that the 'meat' portion of my diet is supposed to provide a good portion of my micronutrition I wouldn't want to (or be able to) just 'supplement' in what was lost. It wouldn't be plausible or desirable to just eat 5x more brocolli, on the side of my foul-tasting, but now drained of nutrients, kidneys!

E35e3d76547b18096a59c90029e7e107

(15613)

on June 21, 2012
at 08:39 AM

Thanks Blitherakt, though I didn't ask about 'destruction.' It seems pretty clear that if I'm soaking and pouring off a lot of red liquid (to remove the blood/urea) then some compounds must be being lost from the kidneys- after all, that's the point! The only question is what nutrients are being poured off with the blood, urea etc. Also my ONLY motivation for eating kidneys rather than muscle meat is the fact that they're far more nutritious. They are definitely less tasty...

A4216f1b1e1f5ab3815bd91700905081

(1646)

on June 21, 2012
at 06:35 AM

Hmmmm... The "rabbit" qualifier was oddly omitted in the comment.

A4216f1b1e1f5ab3815bd91700905081

(1646)

on June 21, 2012
at 06:26 AM

Chicken (and to a lesser degree) kidneys are generally included in the "remove giblets before cooking" package.

Cbda678b2a6bf0537d8c4ea0ce8aa9ad

(4319)

on June 18, 2012
at 01:58 PM

haha... i guess i shouldn't believe everything i read.

44739854bd06eb5c32af5d33aa866864

(859)

on June 18, 2012
at 01:05 PM

A lot of cook books recommend soaking liver in lemon juice before cooking. I've tried this, and it works wonders for taste. I tried it with kidneys and it helped too... So, I'm curious if anyone has any insight into soaking with lemon juice as well (kidney/liver)?

44739854bd06eb5c32af5d33aa866864

(859)

on June 18, 2012
at 01:01 PM

That was my experience in the past too David... the longer I cooked them, the less "urine" I smelled.

E35e3d76547b18096a59c90029e7e107

(15613)

on June 18, 2012
at 12:10 PM

Thanks Thyme. Boiling them is my noruesmal method and I normally drink the cooking liquid. My worry is that soaking them for hours and discarding the liquid will drain more nutrients. The Ken Hom method sounds effective, but I think I'd worry that this too was just draining the nutrients.

E35e3d76547b18096a59c90029e7e107

(15613)

on June 18, 2012
at 09:19 AM

Hmm, all the kidneys I've bought smell distinctly of urine when fresh somewhat decrease in smell after stewing them for ages in linear proportion to how much they're cooked (although during this time the smell permeates all of the rest of the house, so it's not much of an improvement).

E35e3d76547b18096a59c90029e7e107

(15613)

on June 18, 2012
at 09:14 AM

I've never seen rabbit kidneys (or chicken kidneys, which I suppose might be more common) unfortuntely, only beef, lamb and pork.

E35e3d76547b18096a59c90029e7e107

(15613)

on April 12, 2012
at 04:56 PM

Thanks Matt. That makes sense for the fat-soluble nutrients (not that the kidneys contain many), but I'm still worried about the water-soluble ones. After all, there are presumably proteins in the liquid soaking out of kidneys and when you boil foods they certainly do leach nutrients out into the cooking water...

A968087cc1dd66d480749c02e4619ef4

(20436)

on April 10, 2012
at 05:04 PM

If you soak your head, will it remove your brain? Yes. Yes, it will.

E69cdc23a8d09c3bc46a16695276f42b

(123)

on April 10, 2012
at 03:49 PM

I have wondered about liver, too!

C250cd5da05ca54ad3133630ff614573

(175)

on April 10, 2012
at 03:40 PM

I also wonder whether soaking liver in milk removes the nutrients.

C250cd5da05ca54ad3133630ff614573

(175)

on April 10, 2012
at 03:40 PM

I also wonder whether soaking liver in beef removes the nutrients.

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6 Answers

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3
C1484e8cfca0cc00f40da25d36f689b8

(374)

on June 18, 2012
at 04:34 PM

I would be surprised if there was significant loss of nutritional value in a soak in water.

The fat soluble vitamins are very unlikely to leach out as they are hydrophobic so vitamin A, D, E, and K are safe.

Most of the metals are going to be bound up in either enzymes or metallothionein, a sulfur rich protein that chelates metals produced in large amounts in the kidney and liver. As far as I understand it, they often use some type of chelating agent like EDTA to remove the metals from proteins as they don't tend to come out easily. This suggests that little of the metals will be lost in the process of a water soak.

The water soluble vitamins do obviously pose a potential risk for loss. The vitamins that are water soluble will most likely have some polar groups like aldehydes or hydroxyls that cause it to like water in the first place. Proteins tend to have a significant amount of these polar groups as well, which leads to hydrogen bonding keeping them closely attached. In order for them to leach out into the water, those bonds would have to be hydrolyzed, which isn't necessarily impossible and may be favorable entropically. However, reactions tend to be significantly slower at lower temperatures, and I would imagine you aren't using hot water to soak the kidneys. The time spent soaking also makes a big difference as this is a diffusion process. If you don't leave them in hot water for a long time I suspect you'll get the vast majority.

Even if you are boiling them, the cells that contain the vitamins would need to be broken, then the vitamins would have to diffuse out of the food into the water. Most likely any considerable loss would be on the outside layers. You could always cook it sous vide and drink the broth, then no loss.

E35e3d76547b18096a59c90029e7e107

(15613)

on June 21, 2012
at 08:48 AM

Thanks Astar. I wasn't aware that kidneys contained much A, D, E. The point about chelating is interesting, hope it's right. I soak them overnight/a day, repeatedly changing the water. That's necessary to remove the smell (and there's still red stuff leaking by the end). Do you know of any reason to think that I'm not pouring off the relevant proteins during this process?

5
32f5749fa6cf7adbeb0b0b031ba82b46

(41747)

on April 10, 2012
at 05:27 PM

You're not likely removing nutrients. Fat-soluble vitamins are going to associated with the fat, which won't be dissolving in your soaking liquid. Water-soluble vitamins/minerals like to stick to proteins, so again, you're not likely to pull appreciable amounts of nutrients away from the meat.

Getting rid of ammonia, urea, other nitrogenous (and stinky) compounds via a soak sounds like a win to me. In the end, if it means you're more likely to eat the food, they'll be getting more nutrients in!

E35e3d76547b18096a59c90029e7e107

(15613)

on April 12, 2012
at 04:56 PM

Thanks Matt. That makes sense for the fat-soluble nutrients (not that the kidneys contain many), but I'm still worried about the water-soluble ones. After all, there are presumably proteins in the liquid soaking out of kidneys and when you boil foods they certainly do leach nutrients out into the cooking water...

2
Ebb10603524dd22621c1155dd7ddf106

(19150)

on April 10, 2012
at 03:47 PM

I don't think the uric acid in them can be considered a "nutrient" in the good sense. Hypothetically, if the solution you soaked them in was isotonic to the cells of the kidney, and yet still broke down the uric acid, you'd probably have most (if not literally all) of anything you'd considered a nutrient still there.

I don't bother soaking kidneys, however I like to eat small kidneys (rabbit, etc). The flavor at that size is "good" to my senses. A quick pan-fry, a dash of salt and thyme - BOOM - delicious kidneys.

E35e3d76547b18096a59c90029e7e107

(15613)

on June 18, 2012
at 09:14 AM

I've never seen rabbit kidneys (or chicken kidneys, which I suppose might be more common) unfortuntely, only beef, lamb and pork.

A4216f1b1e1f5ab3815bd91700905081

(1646)

on June 21, 2012
at 06:35 AM

Hmmmm... The "rabbit" qualifier was oddly omitted in the comment.

E35e3d76547b18096a59c90029e7e107

(15613)

on June 21, 2012
at 08:43 AM

Also, I'm not thinking of uric acid as a nutrient or worried about its loss. Is there actually any solution that I could practically use that would guarantee the loss of the smell *and* the maintenance of all the nutrients? Cos I just use water, which is probably not 'isotonic to the cells of the kidneys'...

A4216f1b1e1f5ab3815bd91700905081

(1646)

on June 21, 2012
at 06:26 AM

Chicken (and to a lesser degree) kidneys are generally included in the "remove giblets before cooking" package.

1
6c08e876b450e9b28964b9ec262ac1de

(75)

on June 18, 2012
at 11:44 AM

Nutrition: Kidneys are a good source of the B vitamins, which are water soluble. I doubt that soaking them in water significantly reduces their vitamin content, however. The USDA database indicates that kidneys cooked by simmering in water are somewhat less rich in B vitamins than raw kidneys, but even the simmered kidneys are B powerhouses.

Raw, 100 grams http://nutritiondata.self.com/facts/beef-products/3466/2

Simmered, 100 grams http://nutritiondata.self.com/facts/beef-products/3467/2

Smell: If soaking doesn't kill the kidney scent for you, try cleaning and scoring the kidneys in a criss-cross fashion and then tossing them with 1 tsp of soda bicarbonate. Let stand for 20 minutes, rinse well, then toss the kidneys with 2 tsp of vinegar and 1 tsp of salt. Let stand in a colendar, draining, for 30 minutes. Blot dry before cooking. I learned this technique from Ken Hom's "Chinese Cookery," and it's the only technique I've used since.

E35e3d76547b18096a59c90029e7e107

(15613)

on June 18, 2012
at 12:10 PM

Thanks Thyme. Boiling them is my noruesmal method and I normally drink the cooking liquid. My worry is that soaking them for hours and discarding the liquid will drain more nutrients. The Ken Hom method sounds effective, but I think I'd worry that this too was just draining the nutrients.

1
Cbda678b2a6bf0537d8c4ea0ce8aa9ad

(4319)

on June 18, 2012
at 08:24 AM

I read (somewhere) a long time ago, that it was "overcooking" the kidneys which caused the urine smell/taste. A quick pan fry as described by greymouser might be the solution.

Funny coincidence, because I actually buy a few kilos of (pig) kidneys weekly and feed them raw to my cats. They are 1,50 euro/kg where I live, from freshly killed pigs.

E35e3d76547b18096a59c90029e7e107

(15613)

on June 18, 2012
at 09:19 AM

Hmm, all the kidneys I've bought smell distinctly of urine when fresh somewhat decrease in smell after stewing them for ages in linear proportion to how much they're cooked (although during this time the smell permeates all of the rest of the house, so it's not much of an improvement).

44739854bd06eb5c32af5d33aa866864

(859)

on June 18, 2012
at 01:01 PM

That was my experience in the past too David... the longer I cooked them, the less "urine" I smelled.

Cbda678b2a6bf0537d8c4ea0ce8aa9ad

(4319)

on June 18, 2012
at 01:58 PM

haha... i guess i shouldn't believe everything i read.

0
A4216f1b1e1f5ab3815bd91700905081

on June 21, 2012
at 06:30 AM

Real "destruction" of nutrients really only occurs at high-temperature or long exposure to heat methods. Even then, the compounds often eliminated are easily replaced by other sources. Make it taste good, then supplement with alternative sources before freaking out.

E35e3d76547b18096a59c90029e7e107

(15613)

on June 21, 2012
at 08:39 AM

Thanks Blitherakt, though I didn't ask about 'destruction.' It seems pretty clear that if I'm soaking and pouring off a lot of red liquid (to remove the blood/urea) then some compounds must be being lost from the kidneys- after all, that's the point! The only question is what nutrients are being poured off with the blood, urea etc. Also my ONLY motivation for eating kidneys rather than muscle meat is the fact that they're far more nutritious. They are definitely less tasty...

E35e3d76547b18096a59c90029e7e107

(15613)

on June 21, 2012
at 08:41 AM

... And given that the 'meat' portion of my diet is supposed to provide a good portion of my micronutrition I wouldn't want to (or be able to) just 'supplement' in what was lost. It wouldn't be plausible or desirable to just eat 5x more brocolli, on the side of my foul-tasting, but now drained of nutrients, kidneys!

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