Spice rub is any mixture of ground spices that is made for the purpose of being rubbed on raw food before the food is cooked. The spice rub forms a coat on the food. The food can be marinated in the spice rub for some time for the flavors to incorporate into the food or it can be cooked immediately after it is coated in the rub. The spice rub can be left on or partially removed before cooking.
The spices are usually coarsely ground. In addition to spices, salt and sugar may be added to the rub, the salt for flavor and the sugar for caramelization. The simplest rub is just coarsely ground black pepper as in steak au poivre.
Spice rubs can also have ingredients such as herbs, crushed garlic or oil added to make a paste.
Spice rubs are mainly used for preparing meats and fish. There are many different recipes for rubs and most of them are targeted towards a specific kind of food. The exact combination of spices that makes a good rub for a particular kind of food varies from region to region and culture to culture.
Cooking with rubs is almost always done using the dry heat method of cooking where almost no water based liquid is used in cooking. The most popular cooking method for food prepared using a spice rub is grilling. Baking and pan roasting are other dry-heat methods. Sautéing is another method, especially if the spice rub includes flour or bread crumbs.
When water is used for cooking, it is usually after the food has already been partially cooked with the dry heat method.