A microwave oven is a sealed box or chamber with a fan to vent the chamber and a source of microwave radiation. Food is placed in the chamber and is bombarded with microwave radiation. This "excites" water molecules in the food, which become hot generating steam and heating the foodstuff around it. Microwaving is a similar process to steaming and food will not brown.
Microwaves penetrate deeper into foods than heat (infra-red) energy but do not cook from the inside out. If a block of butter is placed in a microwave oven for a short time, heat builds up in the centre and so the centre melts before the outside. Heat can build up in foodstuffs and is not able to escape and this can cause burning or other undesirable effects so it is important to follow manufacturer's instructions and test cooking processes carefully.
Microwave cookery involves the transfer of energy to the food in the form of electro-magnetic radiation. These microwaves penetrate the food and rapidly move the molecules of liquid it contains. This creates friction, which in turn creates heat to cook or reheat food.
Microwave ovens are designed so that the microwaves bounce around inside them, penetrating food from all angles. Microwaves can move through some types of containers as it is only when the waves reach the water molecules in the food that friction is created. Please see the chart below for a full description of the types of containers that can be used in a microwave oven.
Microwave ovens are convenient and useful appliances but they do have some limitations:
Microwave cookery however is particularly useful for:
Foods suitable for microwave cookery
Ideally, only microwave foods that have high moisture content, such as:
Utensils and equipment for microwave cooking
Exposure to the radiated energy can be dangerous so it is important to take care when using microwave ovens. These appliances must be properly maintained - keep the unit clean and check doors and seals regularly to make sure that microwaves can't escape while the appliance is running.
Food containers made from certain materials are unsuitable for use in a microwave oven as they prevent the waves of energy passing through and reaching the food.
Materials that are suitable for use in a microwave oven include:
The shape of the container is also important in microwave cookery. A round shape is desirable as the food will absorb the microwave energy more evenly than in an oval, rectangular or square shaped container.