Marinades are a mixture of liquids, herbs and spices that are used to add flavor, tenderness and moisture to meats, poultry, seafood and vegetables. The combination of ingredients used in a marinade can vary, but generally includes a combination of an acidic ingredient, like vinegar or citrus juice, oil, and herbs and spices. The acidic ingredient helps to break down the proteins of the food, making it more tender, while the oil helps to coat and protect the food from becoming dry during the cooking process. Herbs and spices add flavor and depth to the marinade. Most marinades can be used for any type of food, but some are best suited for specific types, such as seafood marinades for fish and shrimp, or herb marinades for chicken. Marinades should be used for a minimum of two hours, but can be used for up to 24 hours, depending on the type of food being marinated.