To cook food in hot fat deep enough to completely cover the item being fried. The oil or fat used for deep-frying should have a high smoke point (the point to which it can be heated without smoking). For that reason, butter and margarine are not good candidates for frying; shortening, lard and most oils are. The temperature of the fat is all-important and can mean the difference between success and disaster. Fat at the right temperature will produce a crisp exterior and succulent interior. If it's not hot enough, food will absorb fat and be greasy; too hot, and it will burn. An average fat temperature for deep-frying is 375°F, but recipes differ according to the characteristics of each food. To avoid ruined food, a special deep-fat thermometer should be used. Most thermometers used for deep-fat are dual-purpose and also used as candy thermometers. Though special deep-fat fryers fitted with wire baskets are available, food can be deep-fried in any large, heavy pot spacious enough to fry it without crowding. To allow for bubbling up and splattering, the container should be filled no more than halfway full with oil. Fat or oil used for deep-frying may be reused. Let it cool, then strain it through cheesecloth and funnel into a bottle or other tightly sealed container before refrigerating.