How does soaking liver in milk work?

My knowledge about the phenomenon itself is limited but I did see it mentioned in "Modernist Cuisine" (Nathan Myhrvold, p. 147)

Many recipes for foie gras, liver, sweetbreads, and other offal include a soaking step before cooking. For kidneys, this step serves a very simple purpose: to remove any trace of the animal's bodily fluids. Recipes often call for soaking foie gras, liver, and sweetbreads in milk. It is often said that milk improves the taste, purges blood, lightens the color, or affects some other property of the meat. We were skeptical, so we tried several experiments. With a mild-flavored organ meat like foie gras, we could taste a difference, but, frankly, in our tests, we prefer the taste of water-soaked to milk-soaked foie gras. With stronger-flavored organ meats, there is even less of a difference than with foie gras. So our suggestion is to simply soak the meat in water.

So, there you have it.

The milk has caeisin wich pulls out blood and impurties as well as some metallic elements. Same stands for tapia as it pulls out some of the muddy and overpowering stony elements. I have put in 12 years in kitchens and have seen milk used in many soaking applications mostly for cleansing methods.

Milk is very close to neutral pH, hardly worth calling acidic, but it does contain lots of calcium, and is a buffering agent, meaning it will tend to pull strong acids or bases closer to it's own pH.

Any time you soak meat in fluid with different salt content, it is going to cause fluid to flow in and out of the meat, this is the same way brining a turkey makes it more juicy, but the fluids can end up flowing in both directions, diluting whatever water soluble compounds are in the meat.

I'm not so sure that the milk actually neutralizes the liver taste so much as dilutes it, and then you throw the milk, with its portion of the flavor, away. If the milk was neutralizing rather than diluting, I'm sure at least half of the old recipes would tell you to do something useful with that leftover milk, like make a white gravy...

I have done the milk thing and never noticed any real difference in either the texture or the flavor. Maybe its just me. What I did notice is "how" you cook the liver. A Hot pan so when the liver hits it it shrinks right now. Flip it and cook the other side a short time then out and into an already prepared bacon and onion mix to simmer for awhile followed by beef gravy and serve. Mashed potatoes and a vegetable go great and boy is that ever good. While I was a prisoner (NOT a convict) in a South American lock up my cell mate made this our Sunday night special. The Two cane Kid

As a child my mother would soak liver in a bowl of milk for a day and a half regularly replacing the milk and washing the liver before cooking it. What I noticed is that the blood from the liver would seep out into the milk and the liver would have absorbed some of the milk. I can't remember what she said about the milk treatment but it had something to do with the acids in the milk detoxifying the organ and helping remove the acidic bitterness of the liver. I think the acids break down the toxins and the absorption of the milk into the organ helps it retain moisture whilst at the same time flushes out the bitter tasting blood with all the toxins.

My mother said the milk helps neutralize the liver. Blood (liver) being slight basic and milk being slightly acidic together become neutral.

You shouldn't soak a liver in milk as that would make the iron in the liver essentially useless to your body, soak it in water.

Milk contains calcium, and that will bind with iron ... and make it less bioavailable possibly. We are warned not to take iron supplements at the same time as dairy products. Also, milk contains sugar - in combination, the binding and sweetening may make the liver more mild-tasting than it would be otherwise. The liver is not the organ that produces urine, those are the kidneys which should be well washed also.

My mother and grandmother soaked liver in milk prior to cooking. When I moved out on my own I ignored that step and stopped eating liver. I can't explain the chemical process but I can say it does work, by soaking the liver (chicken or beef) in milk for an hour or two prior to cooking makes the dish less bitter. I have also learned adding some cream at after cooking the liver and letting that simmer I have a nice thickened sauce. I think, at least most of the time, cooking techniques learned through generations may be the best.

I could be wrong but my reasoning is that heme iron - the type of iron in chicken liver - is not destroyed by milk. Milk is virtually pH neutral when liver is soaked in it it softens the texture and neutralizes any residual urine. All water does is wet your liver making one use more paper towels to pat the liver down and absorb the excess water.

Reading these explanations, debunkings it seems to me, in large part, and taken as a whole, I'm led wonder if there's another answer entirely.

Calf liver is considered better than more mature beef liver, more tender, milder flavor, etc., and it is lighter in color. What if the milk soaking technique originated as a way to 'improve' the color of the liver? Then as the technique was handed down, it would be a natural process for people to make assumptions as to the reasons the technique was beneficial.