Traditionally, smoking food was used as a preservation technique. The food is indirectly exposed to the smoke from a wood fire long enough to kill bacteria, dry the food, and impregnate it with a smoky flavor. Almost any wood can be used ,but hickory, mesquite, beech and oak are common.
Smoking is now used primarily to impart flavor to foods. Smoking varies from 20 minutes to several days depending on the desired result. Shorter exposures are usually coupled with higher heat that serves to cook the food while the smoke adds flavor. Longer times result in a dry cooked food. Many foods that are smoked longer are also soaked in brine (salted water) prior to smoking such as with a smoked salmon or smoked ham.