The disadvantage is that food which is microwaved does not undergo some of the chemical reactions, such as browning, which makes the food visually attractive. Microwave ovens often do not cook evenly, leading to a concern that bacteria easily killed by more traditional cooking methods may survive the quick cooking time in "cold spots", though the food item as a whole is cooked to a safe average temperature. This can be overcome by leaving the food to stand for a few minutes when cooking is completed. Some high-end microwave ovens are combined with a convection oven which basically cook the food using microwave and hot air simultaneous to achieve both the fast cooking time and browning effect. The convection cooking part is unrelated to the topic of this article.
Using a microwave for cooking large amounts of food is awkward, hence it has been of limited usefulness in a commercial setting. However microwave ovens are used in some fast food chains and special microwave bags are available for cooking fowl or large joints of meat in a microwave.
Because of these properties, professional chefs generally recommend using microwaves for a limited set of tasks, including: melting fats (such as butter) and chocolate, cooking grains like oatmeal and grits, thawing frozen meats and vegetables before cooking by other methods, quickly reheating already-cooked foods, and boiling water.
Boiling water does add another danger, however: superheating. In a microwave, water can be raised quickly to a temperature above the boiling point before major bubbles form, especially if it is purified and in a very clean glass vessel. When water in that state is disturbed, it can suddenly and unexpectedly boil violently, leading to a risk of scalding.
Care should be taken when removing heated water from a microwave. Make sure that the hands are protected from possible liquid boil-over, place the container on a level, heat-proof surface and stir liquid with a warm spoon. Also, never add powdered substances (such as instant coffee or cocoa mix) to the container taken from the microwave; it is advised that the water is poured slowly into another container that already contains the powder.
Never put any metal inside a microwave, unless it is part of a specifically microwave-approved product. Electrical arcs may short-cut through the metal, possibly damaging the oven or starting a fire. Even plates or mugs with metal trim can be dangerous.
See also: Microwave oven