A too-low temperature will make the food greasy. A too-high temperature
will overcook the food's exterior by the time its interior is properly cooked. Take the case of breaded or batter-coated chicken. When it is submerged in sufficiently hot cooking oil, the coated surface quickly forms a protective shield. This wrapping prevents the oil from penetrating to the chicken and therefore helps keep it from becoming greasy. If the oil is not hot enough, unwanted oil will reach the chicken before the outer protective layer can form. If the oil is too hot, the breaded or batter-coated wrapping will be burned by direct heat from the oil before the chicken has had time to cook by conduction. The proper temperature varies by the kind of oil and the type and thickness of the food. As a general rule of thumb, the magic number for cooking breaded or batter-coated foods in vegetable oil is about 375 degrees F. You can use a cooking thermometer
to measure that.
** Asian Recipes