Basic Principles.

Microwaves are a form of energy which are absorbed by the food placed inside the microwave oven cavity. Microwaves make the water molecules inside the food vibrate so that they rub against each other causing friction. It is this friction that produces the heat that actually cooks the food.

Energy → Vibration → Friction → Heat → Cooking

So, increasing the amount energy increases the heat inside the food. To produce more energy you either increase the power level, if your machine has variable power settings, or you have to increase the cooking time.

Cooking in a microwave oven is different to any other type of cooking and you have to use different methods because:-

In a microwave the heat is produced INSIDE the food.
In all other cooking methods, heat is applied from OUTSIDE.
Microwave energy penetrates the food to a depth of about 25mm.
Microwaves are similar to light and they are emitted downwards from the top of the microwave oven cavity. The waves bounce off the metal sides of the cavity, hitting the food from different angles. Theses microwaves do not hit the food evenly. To minimise this effect, the oven either has a rotating turntable or a paddle wheel in the roof to stir up the microwaves but there are still problems with uneven heating.

Major Problems with Microwave ovens.

1. Food cooks very quickly and is liable to be overcooked.
2. Hot and cold spots can occur producing food that is unevenly cooked.
3. Microwaves cannot brown food as no heat is applied from the outside.
4. The outer edges of the food get hot while the centre remains cool.
5. Metal pans, plates, utensils etc. will permanently damage the microwave generator.
6. Cooking small quantities of food can damage the microwave generator.
7. Never turn on an empty oven as it will damage the microwave generator.
8. Waste food left on the inside of the oven cavity absorbs energy.
9. Salt added at the beginning of cooking toughens food especially meat.
10. Not all foods can be cooked in a microwave.
11. The size of the oven cavity limits the quantity and size of the food to be cooked.

Advantages.

Microwave ovens rapidly cook foods, heat liquids and defrost frozen foods. Some foods are better cooked in a microwave oven as they retain more flavour, texture and goodness. (eg. plain fish, soft fruit, peas, fat free cakes). Microwaves are safe and economical on electricity with savings up to 50%. No oven preheating is required and the kitchen stays cooler. Cooking is cleaner with less odours. Washing up is reduced. A microwave oven can be used with a conventional oven to speed up the cooking such things as bread.

Microwave cooking methods.

1. Undercook foods rather than overcook. Because of the rapid speed of cooking, it is easy to misjudge the cooking time. It is simple to give it a short extra burst of heat.
2. Cooking does not stop when you turn off the energy. It goes on cooking as the heat on the outside travels to the middle of the food by conduction. This additional cooking must be taken into account especially in large thick solid foods. This period of time is called the STANDING or RESTING TIME. Cakes should be taken out of the oven while the top is still slightly moist.
3. Some recipes include a 'resting time' during the cooking process to allow the heat to reach the centre of the food. This is especially important when cooking chicken from frozen otherwise the centre will remain uncooked and cause food poisoning.
4. Any liquids such as stews, soups, drinks etc. must be stirred to avoid cold spots.
5. Solid foods must be carefully arranged on the plate to get an even cooking. During cooking they should be rearranged so that the sides facing inwards are turned outwards.
6. Different sizes of solid foods such as potatoes, cakes, etc. will cook at different rates so try to make them all the same size.
7. When heating small amounts of food, always place a glass of water in the oven to absorb the excess energy so as not to damage the microwave generator.
8. Seasoning should be adjusted at the end of cooking. Use less spices.
9. Wipe down the inside of the oven after use.
10. Use glass, china, pottery and plastic plates and containers but make certain that they are suitable for use in the microwave oven. SOME ARE NOT. No metals can be used. Metallic glazed pots can cause problems.
11. Thin plastics will melt but Clingfilm can be used for lining the dishes to minimise washing up. Clingfilm can also be used for covering containers but it should be spiked to let steam escape.
12. Plastic and wooden spoons and spatulas can be left in the food when cooking.
13. Paper towels can be used to line the oven floor and cover containers of avoid splattering. Food can be placed on paper towels during cooking to absorb moisture.
14. Food can be browned if special ceramic containers are used.

Foods not microwaveable.

Yorkshire puddings, pancakes, meringues, eclairs, soufflés, scones, crisp pastry, hard eggs and rich cakes made by the creaming method. Egg dishes can be cooked but boiled eggs explode.

Power Settings.

To find the maximum power rating, look at the rating plate usually on the back of the casing.
Do not use the higher input rating. Look for the OUTPUT rating such as 650 Watts.
In conventional electric or gas ovens, you control the heat by reducing the amount of fuel being used by turning down a control knob.
Microwaves can not be turned down. They can either be on at full power or off. So to control the heat settings, the microwaves are turned on at full power for a period of time and then turned off for a period of time. The controls vary the amounts of on/off time.
Newer microwave ovens have higher maximum power outputs and can have many heat settings so it is vital to follow the manufactures instructions and be prepared to experiment. Remember to undercook. Temperature settings in normal recipes cannot be used.

CAUTION The heat settings and cooking times will vary for different ovens.