Shirley O. Corriher

There is a commonly held belief that soaking a tough cut of meat in a marinade will make it tender. Sadly, this just isn't true much of the time. While some marinades are very successful at adding flavor to meat, chicken, and fish, they are, with one exception, a disaster at tenderizing.

The two most popular types of marinades are acidic (made with citrus, vinegar, or wine) and enzymatic (made with ingredients such as pineapple and papaya). Although both types work primarily on the surface of the food, they lead to different results: highly acidic marinades can actually toughen food, while enzymatic marinades can turn the surface of the food to mush. For true tenderizing, the most effective marinades are those that contain dairy products.

One marinade family relies on mildly acidic ingredients, like citrus juice, vinegar, or wine.

Acidic marinades "denature" proteins. Imagine the protein in raw meat, chicken, or fish as individual units of coiled ribbon, with bonds holding each coil in a tight bundle. When these proteins are exposed to an acidic marinade, the bonds break and the proteins unwind. Almost immediately, one unwound protein runs into another unwound protein and they bond together into a loose mesh. (This is the same thing that happens when proteins are exposed to heat.)

At first, water molecules are attached to and trapped within this protein mesh, so the tissue remains juicy and tender. But after a short time, if the protein is in a very acidic marinade, the protein bonds tighten, water is squeezed out, and the tissue becomes tough. If you've ever tried marinating shrimp in highly acidic ingredients, it's likely that you're familiar with this result.

In limited cases, mildly acidic marinades can add wonderful flavor to fish and meat, especially if you enhance the mixture with fresh herbs, spices, or perhaps another liquid like Worcestershire sauce. The key is to use the correct strength acid for the food you're marinating. For shrimp, I use a low-acid marinade (perhaps one part mild acid to four parts oil) to avoid toughness. For example, I might use two tablespoons each of vinegar and caper juice and one cup of oil.

A fairly tight-textured cut of meat like flank steak can survive a more acidic marinade. Since the marinade only penetrates a fraction of an inch, it won't toughen the meat.

Another approach is to use enzymatic marinades, which work by breaking down muscle fiber and collagen (connective tissue). Raw pineapple, figs, papaya, honeydew melon, ginger, and kiwi all contain such enzymes, known collectively as proteases (protein enzymes). Unfortunately, these enzymes work almost too well, turning tough meat muscle into mush without passing through any intermediate stage of tenderness. The longer the meat marinates, the greater the breakdown of proteins and the mushier the texture.

My experience with tenderizing enzymes mirrors that of Dr. Nicholas Kurti, a famous Oxford physicist who tried tenderizing a pork roast by injecting half with pineapple juice, leaving the other half untouched. A noted chef, Michel Roux, was to judge on television which side was better. After cooking, the half treated with pineapple was total mush and looked like a pile of stuffing. Not surprisingly, Chef Roux preferred the untreated half. (He did try to find something nice to say about the mushy half. Noticing its crisp skin, Chef Roux announced, "But the crackling is superb!" Dr. Kurti used the comment as the title for his book on his experiments with tenderizing enzymes.)

Most commercial meat tenderizers rely on enzymes to do their "tenderizing" (a papaya enzyme, papain, is a common ingredient in these products), so I stay away from them.

Dairy products are, in my opinion, the only marinades that truly tenderize. Hunters have long known to marinate tough game in milk, Indian recipes use yogurt marinades for lamb and tough goat meat, and some southern cooks soak chicken in buttermilk before frying. Buttermilk and yogurt are only mildly acidic, so they don't toughen the way strongly acidic marinades do. It's not quite clear how the tenderizing occurs, but it seems that calcium in dairy products activates enzymes in meat that break down proteins, a process similar to the way that aging tenderizes meat.

In deciding how long to marinate, consider the texture of the meat or fish. In general, open-textured flesh like fish fillets needs only a few minutes of soaking. I love making "fish fingers" by briefly immersing strips of fish fillets in buttermilk seasoned with cayenne, dusting them with seasoned flour, and then frying them. Food with a tighter texture, such as chicken or lamb, can tolerate several hours in a marinade, even one that's mildly acidic.

Shirley O. Corriher

Roasted turkey breast, sautéed pork chops, and stir-fried shrimp all tend to suffer a common fate when they're cooked even a few minutes longer than necessary: they get dry and tough. Actually, any kind of meat or fish will taste like shoe leather if it's severely overcooked, but turkey, pork, and shrimp are particularly vulnerable because they're so lean. Luckily, there's a simple solution (literally) for this problem. Soaking these types of leaner meats in a brine -- a solution of salt and water -- will help ensure moister, juicier results.

Moisture loss is inevitable when you cook any type of muscle fiber. Heat causes raw individual coiled proteins in the fibers to unwind -- the technical term is denature -- and then join together with one another, resulting in some shrinkage and moisture loss. (By the way, acids, salt, and even air can have the same denaturing effect on proteins as heat.) Normally, meat loses about 30 percent of its weight during cooking. But if you soak the meat in a brine first, you can reduce this moisture loss during cooking to as little as 15 percent, according to Dr. Estes Reynolds, a brining expert at the University of Georgia.

Brining enhances juiciness in several ways. First of all, muscle fibers simply absorb liquid during the brining period. Some of this liquid gets lost during cooking, but since the meat is in a sense more juicy at the start of cooking, it ends up juicier. We can verify that brined meat and fish absorb liquid by weighing them before and after brining. Brined meats typically weigh six to eight percent more than they did before brining -- clear proof of the water uptake.

Another way that brining increases juiciness is by dissolving some proteins. A mild salt solution can actually dissolve some of the proteins in muscle fibers, turning them from solid to liquid.

Of all the processes at work during brining, the most significant is salt's ability to denature proteins. The dissolved salt causes some of the proteins in muscle fibers to unwind and swell. As they unwind, the bonds that had held the protein unit together as a bundle break. Water from the brine binds directly to these proteins, but even more important, water gets trapped between these proteins when the meat cooks and the proteins bind together. Some of this would happen anyway just during cooking, but the brine unwinds more proteins and exposes more bonding sites. As long as you don't overcook the meat, which would cause protein bonds to tighten and squeeze out a lot of the trapped liquid, these natural juices will be retained.

How long to brine depends on the size and type of meat you've got. Larger meats like a whole turkey require much more time for the brine to do its thing. Small pieces of seafood like shrimp shouldn't sit in a brine for more than half an hour. In fact, any meat that's brined for too long will dry out and start to taste salty as the salt ends up pulling liquid out of the muscle fibers. (Be sure not to brine meats that have already been brined before you buy them, such as "extra-tender" pork, which has been treated with sodium phosphate and water to make it juicier.)

It's vital to have a brine with the correct salt concentration, especially for lengthy brining times. Small, thin pieces of meat like fish fillets or shrimp can withstand a concentrated brine because they'll be immersed for only half an hour or less. But for longer brines, Dr. Reynolds suggests using 9.6 ounces of salt for every gallon of water. One scant cup of table salt per gallon of water would put you within range.

If you're using kosher salt, you'll need to use more of it by volume. This is because kosher salt has larger crystals and is bulkier than table salt. I actually prefer using kosher salt in brines because it dissolves much faster, and it comes in nice big cartons. Using Diamond Crystal kosher salt, you'll need 2 cups per gallon of liquid. Morton's kosher salt is denser, and you only need 1-1/3 to 1-1/2 cups per gallon of liquid to get the brine concentration that Dr. Reynolds recommends.

Any food-safe nonreactive container is fine for brining. For brining turkeys, I use a plastic turkey cooking bag that will completely enclose the turkey; the meat needs to be completely submerged. I put the turkey in the bag and then set the whole thing in a large bowl. I add water to the bag with a measuring cup, keeping track of how much I've added. Then I add the correct amount of salt. If I'm brining a familiar turkey size and I know the approximate amount of salt, I just rub the salt directly on the turkey, inside and out, before adding the water. I put the bowl in the refrigerator (all meats should be refrigerated during brining) and let the meat soak for 12 to 24 hours. Discard the brine after use; for safety reasons, it should never be reused. (For a slightly different approach, see How to brine your Thanksgiving bird.)

Whatever you're brining, remember to rinse the meat or fish well afterward to remove any surface salt. Properly brined meat shouldn't taste salty, just very juicy with good flavor. But do reduce the amount of salt called for in the recipe; that is, don't add salt until the dish is at a point where you can taste it and judge.

Any lean, dry meat is an ideal candidate for brining; some of my favorites are shrimp, fish fillets, chicken pieces, whole chickens, and pork chops. Keep all meat and fish refrigerated during brining, rinse them well afterwards, and don't overcook them. If you need more liquid to completely submerge the meat, measure more and add it, along with the proportionate quantity of salt.

You can add dried herbs, such as thyme, oregano, or sage, to the brine or rub them directly on the meat for more flavor. You can also supplement or replace the water with another liquid, such as apple cider for a turkey or pork brine. Many brines include sugar, which is fine as a flavor enhancer. But according to Dr. Reynolds, sugar has no technical function when it comes to juiciness; salt is the key ingredient.

The chart below gives salt concentration and brining time for various foods. Concentrations are for Diamond Crystal kosher salt. For table salt, cut salt amounts by 1/2; for Mortons kosher salt, cut amounts by 1/4.

Shirley O. Corriher is the author of CookWise (Morrow).