On Food and Cooking

The Smoke Point Most fats begin to
decompose at temperatures well below their
boiling points, and may even spontaneously
ignite on the stovetop if their fumes come into
contact with the gas flame. These facts limit
the maximum useful temperature of cooking
fats. The characteristic temperature at which a
fat breaks down into visible gaseous products
is called the smoke point. Not only are the
smoky fumes obnoxious, but the other
materials that remain in the liquid, including
chemically active free fatty acids, tend to ruin
the flavor of the food being cooked.
The smoke point depends on the initial free
fatty acid content of the fat: the lower the free
fatty acid content, the more stable the fat, and
the higher the smoke point. Free fatty acid
levels are generally lower in vegetable oils
than in animal fats, lower in refined oils than
unrefined ones, and lower in fresh fats and
oils than in old ones. Fresh refined vegetable
oils begin to smoke around 450ºF/230ºC,