About Marinades

Marinades have two purposes: to tenderize and to enhance the flavor of meat, fish, poultry or even veggies before they are cooked. To my mind, if you have a great steak that is naturally tender and flavorful, it is a culinary crime to marinate it. An average piece of meat, however, can be much improved with a good marinade. To help you master the art of marinating, I have put together a short explanation of how marinades work and a list of "Do's and Don'ts in Marinating."

Tenderizing Ingredients
A marinade must include an acidic component to tenderize the meat. Some of the most popular are:
Citrus juice (Lemon or Orange)
Vinegar (red or white wine, balsamic or cider)
Vinaigrette
Soy sauce
Prepared salad dressings
Tomatoes and tomato sauce
Teriyaki sauce
Yogurt
Extra virgin olive oil and other oils with emulsifiers
Milk and buttermilk
Pineapple juice
Dry sherry
Worcestershire sauce

Flavoring Ingredients
Garlic
Onion
Scallions
Horseradish
Ginger
Mustard
Bell peppers
Fresh herbs and spices

Oil
Oil helps the flavors absorb into fatty tissue. It is best to choose one with high smoke point, as they are the most grill- and flame friendly. In order of highest smoke point:
Safflower oil
Grapeseed oil
Soy or soybean oil
Olive oil
Peanut oil
Sunflower oil
Canola oil

Do's

—Onions or sweet ingredients in a marinade can help form caramelized, crispy coatings on grilled meats.
—Always marinate in the refrigerator. At room temperature dangerous bacteria can grow and lead to food illnesses.
—Place meat in a glass or food-grade plastic container or a heavy zip-top bag with the air squeezed out, and turn often to be sure all surfaces benefit from the marinade. 
—Marinate vegetables for 15 to 30 minutes.
—Marinate fish and seafood for 15 minutes to one hour.
—Marinate poultry for 30 minutes to 3 hours.
—Marinate beef or lamb for at least 30 minutes or as much as overnight.
—Use ¼ cup of marinade per pound of meat.

Don'ts

—Do not marinate very large, thick cuts of meat; they often end up with a mushy exterior and a tough, chewy center.
—Do not puncture the meat to help the marinade penetrate. It gives an uneven result and allows the meat's natural juices to run out during cooking, making the meat dry. 
—Don't use much salt in the marinade. Salt will draw moisture out of your meat, causing it to dry out and prevent flavor from absorbing in. Salt should be added later.
—Do not reuse marinades. Marinades are in contact with raw ingredients, which may contain harmful bacteria. Always discard your marinade after use.
—Don't marinate in metal containers. Metal can react chemically with the acids in the marinade and cause a change in flavor.
—Don't over-marinate fish. Fish is naturally quite tender and can become mushy if marinated too long. Keep marinating times for seafood between 15 minutes and one hour.
—Do not freeze meats in their marinade. Prolonged exposure to the acids in the marinade combined with damage from ice crystals can cause meat to become mushy.