Guide to Microwave Cooking

What are Microwaves?

Based on the principle of radar, microwaves are a form of energy that comprises electro-magnetic, short-length, non-ionising, high-frequency radio waves at the top end of the radio band. They are close to infra-red rays but not as powerful and the frequency is 2450 megahertz (MHz), which translates into literally millions of cycles or vibrations per second. The word ‘hertz’ comes from Heinrich Hertz, the scientist who first discovered the nature of the waves.

Inside the cavity of a microwave oven, with its extraordinary number of compulsory cut-outs and safety devices, the microwaves are completely confined and are unable to leak out and attack you. In any event, microwaves are an altogether different kettle of fish from X-rays, gamma-rays and ultra-violet rays, which are ionising and known to cause dangerous cellular alterations to the body with minimal or no temperature change.

Microwaves have none of these effects and, more importantly, are non-cumulative. Leaks can occur only if the oven is worn, damaged or mishandled, and for safety reasons it should be checked from time to time by a qualified engineer to make sure the door fits snugly, the seal around the door is secure, and the hinges are not rusty.

If the door front fractures, stop using the oven at once and request a service call as soon as possible. So what would happen if one were, briefly, exposed to microwaves? The answer is a burn, which is never pleasant. Therefore look after your oven, keep it serviced and clean it regularly.

How Microwaves Cook Food

When the microwave is plugged into a socket, the door closed and oven switched on, microwaves are emitted from a magnetron (or microwave energy generator) usually on one side at the top, protected by a cover, generally plastic. The microwaves are transmitted into the inside of the oven cavity down a channel called a waveguide, bounce off the sides and ‘beam’ on to the food from all directions. Instantaneously, the food absorbs the microwaves, which cause the water molecules within the food to vibrate.

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The result is excessively rapid friction that creates enough heat to cook food. For a simple demonstration of how friction makes heat, rub your hands together vigorously and feel how warm they become. Now imagine this multiplied umpteen times and you will understand how the microwaves work.

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For even cooking, most models are fitted with a wave stirrer, stirrer blade or paddle (concealed at the top) which helps to distribute the waves. Most also have a rotating turntable so dishes do not need turning during cooking. However, turntables do restrict the shape and size of dishes, so consider buying a model where the turntable can be switched off or removed if necessary.

Successful Cooking

Because microwaves are short-length, high-frequency radio waves, they are able to penetrate only 2.5 cm/1 in of the food in all directions. Thus shallow containers are better than deep ones except those used for some cakes and puddings that need headroom for satisfactory rising. Round dishes give the best results, followed by oval. Sometimes food in rectangular or square dishes cooks unevenly, especially at the corners.

The food will also cook more effectively if thick pieces are arranged towards the outside edge of the dish and not piled up. Stirring during the cooking cycle helps to distribute heat and, where practical, this has been recommended in the recipes. If possible, whole potatoes and other similar-sized foods (apples for example) should be arranged, on a plate or in a dish, in a hollow triangle, square or circle. If your microwave is an older model without a turntable, make sure you turn the dishes several times during cooking.

Resting and Standing Times

For heat to penetrate the food and work its way gently from the outside to the centre, it is recommended that the food be allowed to rest and stand after or during cooking. Some dishes, especially large quantities, turkeys, etc., if cooked without a rest, would become overcooked on the outside but remain undercooked in the middle.

Depending on what is more convenient, food may be left to rest or stand inside or outside the microwave. Individual recipes give guidance on resting and standing. As a further precaution, it is preferable to return an undercooked dish briefly to the oven rather than add extra time initially. The microwaves act so swiftly that even a few too many seconds could spoil the food.

Seasonings

As salt toughens microwaved meat, poultry and vegetables, it should be added half-way through or at the end of cooking. Other seasonings, such as herbs and spices, may be added at the beginning.

Caution

Never operate the oven while empty because without food or liquid to absorb the microwaves they will bounce straight back to the magnetron and shorten its life span. Similarly, melting 5–10 ml/1–2 tsp of fat, or heating just a tiny amount of liquid, will have the same effect, so it is best to place a cup or tumbler of water in the oven at the same time. Just in case it gets switched on by accident, it is a wise safety measure always to keep a container of water inside an empty oven until it is needed for cooking.

Cleaning

Suggestions for cleaning have been given in Hints and Tips. As fresh food spills are so easy to remove from the cool interior of a microwave (nothing burns on in the conventional sense), a wipe over with a damp cloth immediately after use will ensure that it stays spotless and fresh.

Cookware

Metal containers reflect microwaves away from the food and prevent it cooking so metal containers or tins (pans) of any sort should never be used in the microwave. It is also important to note that crockery with metal trims or with the manufacturers’ name or pattern design printed in gold or silver underneath could cause arcing – an effect like tiny flashes of lightning. This arcing not only damages the magnetron but also ruins the metallic decorations. The exceptions here are small amounts of foil used to cover poultry wing tips and ends of legs to prevent scorching, and metal kebab skewers that are well covered by the surrounding food.

However, you must ensure that the skewers do not come into direct contact with any part of the oven interior.

In order for the microwaves to reach the food and subsequently cook it, the dishes chosen should be made of materials through which the microwaves can pass most readily – like rays of sun through a window pane. These are listed below and, although most stay cool or even cold, some kinds absorb heat from the cooked food and feel hot to the touch. For comfort, the cookware should be removed from the oven using oven gloves.

Baskets

These may be used for brief reheating of rolls, etc. Prolonged spells in the microwave cause dryness and cracking.

Clingfilm

Clingfilm (plastic wrap) is excellent for covering and lining dishes. To prevent the film from ballooning up in the oven and bursting, or being sucked back on to the food (the latter is a disaster if it happens to a pudding that is supposed to rise), I have recommended puncturing the film twice with the tip of a knife to allow steam to escape. By puncturing, I mean making a small slit and not a tiny pin-prick.

Glass

Not your best crystal but Pyrex-type glassware is ideal. Corning ware, which is ceramic glass, is also excellent. Other, sturdy, glass may also be used.

Paper

Kitchen towel or paper napkins may be used to line the oven base if food is to be cooked directly on it (paper is a great absorber), and also to cover food to prevent spluttering.

Plastic

Use only rigid plastic; yoghurt or cottage cheese containers or thin plastic may collapse. Look for special microwave utensils made by firms like Lakeland or other reliable makes stocked by specialist kitchen shops, supermarkets and department stores. Note that plastic spatulas are useful as they can be left in, say, a sauce during cooking to use for stirring when required.

Pottery and Porcelain

Both may be used – but not your best china. Avoid dark utensils and ironstone as they absorb heat and take it away from the food.

Roasting Bags

Roasting bags, also called boiling bags, have a hundred and one uses; see-through plastic roasting bags are convenient to use and also clean. They are ideal for cooking joints of meat or poultry. Close the tops with elastic bands or string, not metal ties.

Waxed Paper Products

Like basketware, these dry out in the microwave and should be used only for brief reheating.

Wood

Like basketware, wood dries out in the microwave and should be used only for brief reheating.

Extras

Browning dish: this is a white ceramic dish, the base of which is coated with a special tin oxide material. It becomes very hot indeed when preheated, making it possible to sear food prior to microwave cooking. This gives the food the browned finish associated with conventional grilling (broiling) or frying (sautéing). As the dish needs to be preheated, empty, for varying lengths of time depending on the food being cooked, be guided by your own microwave oven instruction book.

As a general rule, the preheating time should be around 6 minutes for steaks and chops and 2–3 minutes for eggs. It should never be preheated for longer than 8 minutes, nor used in a conventional oven. If you are cooking in batches, the browning dish will need cleaning and preheating for half the initial length of time between batches. Although it will take on a yellowy tinge when hot, the dish will return to its original colour when cool. Preheating this type of dish does not harm the oven.

Temperature probe: this looks like a thick knitting needle attached to a plastic-coated lead and is generally available with the more sophisticated models of microwave ovens to register the internal temperature of food. One end slots into the side of the oven while the sharp end is inserted into the food to be cooked.

The cooking cycle is therefore geared to temperature and not time and when, for example, a joint of well-done beef registers 160°C, the oven will switch off automatically. As every model varies, please refer to your own microwave book before using the probe and setting the temperature.

Thermometer: thermometers for use in microwave ovens are now obtainable and, like temperature probes, they must be used according to the manufacturers’ instructions. Never use a conventional meat thermometer in a microwave, although it can be used to test the meat for doneness when the joint is resting after cooking.

Choice of Microwave Ovens

People often ask me which model I would recommend and I always find this a difficult question to answer. Those who are not technically minded will do best with a fairly basic model that is straightforward to operate and does its job efficiently. Others might find the new models a joy in that they bear some relation to computers and can be easily programmed and manipulated to suit all purposes.

The only advice I can give on the selection front is to suggest a visit to your electricity supply retail store or a department store to have a thorough look at as many ovens as you can and ask for a demonstration. You will then be in a good position to buy what suits you, not what looks fabulous, is very expensive and turns out to be more to cope with than you bargained for.

Power Controls

Most domestic microwave ovens vary between 500 and 850 watt output.

All recipes in this book have been prepared in a 650 watt output oven, and usually use only two power settings: Full, which is 100 per cent power (650 watts), and Defrost, which is 50 per cent (325 watts). If your oven has a different output, the guide below may prove useful. Be warned: if you have a higher wattage output oven, make sure you do reduce cooking times and check a little before the end of your calculated cooking time. You can always cook for a few seconds more.

Using these figures will give a fairly accurate conversion time but for greater accuracy refer to your own microwave oven recipe book. Note that some manufacturers call Defrost 30 per cent power. Check your manual if yours does and you have a 650 watt or less output microwave, in which case use Medium (50 per cent) power where a recipe calls for Defrost. If you have a higher output (650–850 watts), use 30 per cent power instead of Defrost.

There are now technically advanced microwave ovens with variable power settings ranging from 1–10 or from 1–5 (see figures in brackets in the Summary of Settings). The variable settings enable some dishes to be cooked more slowly than others and some users find this advantageous, especially when making stews and casseroles. Some models have a system whereby the power comes on and off automatically; listen and you can hear it happening. Other models have an automatic reduction in output at the lower settings but this is silent.

Colour

Foods cooked in the microwave can look pale and insipid. Hence my inclusion of bastes for roast meat and poultry, a few shakes of soy sauce or a dusting of paprika, beef stock cubes for stews and casseroles, and icings (frostings) for cakes. I have also incorporated a number of other tricks – like using Red Leicester cheese for toppings instead of Cheddar. As you will find out when you make up the recipes in the book, none lacks colour.

Summary of Settings

Even if you have a microwave with variable power settings such as listed above, do not try to convert my recipes, which were all cooked at Full or 50 per cent power.

Reheating

Conventional reheating of meat and poultry, or keeping plates of food warm in a cool oven, can sometimes cause a build-up of bacteria, resulting in mild food poisoning. With a microwave oven, the action is so fast that germs have no time to breed, and the food stays fresh and moist without looking frayed round the edges.

Bonuses

Freshness of flavour and colour, plus retention of nutrients, characterise most foods cooked in a microwave oven. The foods also tend to shrink less, and cooking smells are reduced.

It is encouraging to know that when cooking in the microwave the electricity saved is between 50 and 70 per cent. Also no preheating is necessary and there is minimal residual heat in the oven cavity. It has been estimated that using a microwave is four times as efficient as conventional cooking because all the energy is directed to the food, with no ‘overspill’.

Notes on the Recipes