The temperature at which oil begins to smoke and discolor is called its smoking point. Above this temperature, the oil degrades, giving it an off-taste. Cooking above the smoking point can release irritating substances into the air and into the food. Eating degraded oil can cause stomach distress. Different kinds of oils have different smoking points.
Many oils are available in either refined or unrefined forms.
It is especially good for making salad dressing. Butter is churned cream. Often spread on toast, it can also be used for frying or baking. Unrefined corn oil has a buttery flavor. Margarine is a processed vegetable oil substituted for butter.