The microwave oven is a popular tool for cooking and re-heating foods. Microwaving brings efficiencies in energy use and time and is increasingly popular as we become busier and have less time to cook our meals. The microwave is a very versatile tool, being able to defrost, cook, steam, and reheat a wide range of food products. This heating is brought about by the use of microwaves. These microwaves – a form of radiation - enter the food and cause the molecules to vibrate. This vibration causes friction and thus heat.

My colleague asked me to write an article about the microwave oven, an article that discusses the safety aspects of using a microwave oven.
It seems that there are some fears and stories about radiation, cancer causing chemicals and nutrient killing microwaves. But there are also a large number of voices that assure us that the microwave oven is very safe, causes no harm to us or our food and is an excellent, efficient tool in our kitchen.
So who is correct? The difference in opinion is so great that there seems no way for both sides to be right. So, should we embrace the microwave oven, with all the ease and convenience it brings or throw it out as a killer in our homes?
Honestly, I don't know.

Personally I tend to think that the microwave oven is safe; although it should be used with caution - I'll get to that later. Having said that, do I have a microwave oven at home? No, I don't but that's more of a personal usage issue as I don't really need one at home and I'm happy to use a microwave oven to reheat my meals at the office.

What it Does and How.
A microwave oven uses microwaves - a form of radiofrequency electromagnetic energy to heat food. This energy is in the form of waves and radiation. However it is not the kind of radiation that we have all heard of and understand to be dangerous. Radiation comes in many forms and not all are harmful. Even heat coming from an electric heater is a form of radiation, and similar waves are around us all the time as they send signals to and from our mobile phones, television sets and radios.
The microwaves produced in the microwave oven, are of a particular frequency that has extremely useful characteristics. Microwaves pass cleanly through many materials such as glass, plastics, ceramics and paper, but are reflected by metal. Due to the long wavelength of the microwave the waves cannot pass through the glass door of the microwave oven because of the metal mesh which reflects the waves back into the cooking cavity. This allows us to look inside while the microwaves are kept inside.
Oh, and microwaves have one more interesting property - they can heat things up. Microwaves cause the individual molecules to rotate or move which causes friction and so heat. It does this best on water molecules but also other liquids. It is because the heat is created within the food itself that microwave cooking is so energy efficient. There is no heating of the container or the area around the container. The heat you feel on the plate after heating has been transferred there from the food itself. Also, because the microwaves are acting ‘within’ the food the action is very quick and items can be heated in a short period of time.

Is it bad for the food?
The heating process of the microwave is at the basic molecular level. Some people say the heating process affects, damages or even destroys those molecules. The affects claimed vary from a loss of nutrients, to a molecular change into cancer causing compounds. The claim is that the vibration of molecules by the microwaves, is so strong that the bonds between the molecules are broken down in such a way that the changes are harmful.
Personally I have my doubts about this. The texts I have read when preparing this discussion make little or no differentiation between foods. Surely some foods will be affected differently? Even heating water is supposedly not safe, which I find doubtful.

However, I do know that cooking affects foods chemically. Cooking is itself a chemical reaction brought about by heat. We know that cooking can cause otherwise safe foods to become cancerous or changed nutritionally. Carbon deposits on burnt charred foods are known to be harmful and it is well known that some cooking methods can affect the quantity and quality of nutrients in the food. However there is no single answer on the best and safest way to cook. For example, while some vitamins are known to be water soluble and lost during boiling, other nutrients are only made available to the body after the cooking process helps breakdown food making the nutrients contained available for absorption into our bodies. Of course, let’s not forget that cooking is vital when preparing some foods to destroy otherwise harmful organisms and many foods would be very unpalatable if we had to eat them raw.

One advantage of microwave cooking is the speed and reduction of water used. Similar to steaming, microwave cooking requires a limited amount of nutrient sapping water and the extra speed of the microwave oven means cooking times are kept to a minimum.

So, the simplest and quickest answer to the question of microwave safety is this - there is no simple and quick answer!

Basically it depends. It depends on what you are doing with the food. Cooking or defrosting? What are you cooking? What power and for how long are you cooking? These questions will determine the answer.

Safe Use of a Microwave Oven
As with all cooking methods, there a number of things we should be aware of when using a microwave oven to ensure we are using it safely.

•  Materials. Be aware of what you are putting in the microwave. NO metal dishes. Be aware that some dishes have metal content in their decoration. If you are unsure, put the dish in (with some water) and start the microwave. If you see sparks shut it off straightaway.

•  Plastic containers and cling film wrap should be used with care. Some are not designed to withstand high temperatures and can leach chemicals into food when subjected to high temperatures. To be sure, use only containers labeled as ‘microwave safe’

•  Don’t operate the microwave oven empty. Consider keeping a cup of water inside in case of accidental operation.

•  Obviously foods heated in the microwave will be hot. Even if the outside feels cool be careful, as the inside can be very hot. Mix the food thoroughly or let it stand for a few minutes to distribute the heat evenly. Use a heat protecting glove or similar to remove dishes from the microwave oven. Be especially careful if heating baby food/milk to make sure there are no areas that are excessively hot.

•  When cooking or re-heating foods make sure the food is evenly heated to avoid areas that are undercooked or still cool that may still contain active microorganisms.

•  The microwave oven is made with a number of built-in safety features. Do not try to overcome these. Don’t try to operate the microwave oven with the door open. The glass door has a metal mesh that is designed to prevent microwaves from escaping the oven cavity. Do not remove or damage this mesh. If the door locking mechanism or door mesh is damaged do not use the microwave oven. Have it serviced by authorized personnel or replace it.

•  Keep the microwave oven clean. Especially make sure there is no food debris or other dirt around the door seals that may affect the closed seal.
Despite the microwave blocking case of the oven, microwaves are able to escape from the front glass, although only a very short distance and in limited amounts. To be very safe, do not stand and wait within arms length of an operating oven.

•  Superheating. Superheating occurs when something reaches boiling temperature but doesn't actually boil and bubble. This can happen with liquids in the oven. If you heat a cup of water or your favourite drink, there is a chance an area of the liquid becomes superheated, but is not allowed to boil by the cold liquid surrounding it. Once the liquid moves or is stirred, then the superheated part suddenly and violently boils. If you put a spoon into a cup of superheated coffee the coffee will boil up and possibly give you a nasty burn.
To avoid this, don’t heat liquids for too long. Standing a non-metal utensil like a chopstick in the cup will help the liquid mix and heat evenly. A microwave oven with a rotating turntable will help. When first moving a heated cup, put a spoon or something in first and do so at arms length.

Make sure that whoever is using the microwave is aware of these dangers and teach them well. Especially look out for the young and elderly users.

If you really are concerned about the nutrient sapping, molecule changing aspects of the microwave oven it makes sense to look at the problem logically. One extreme would be to never to use the oven. However a compromise might be to only use it for defrosting or re-heating cooked food.  As with so many things in life, there is no right or wrong answer.

Microwave ovens are undeniably very useful. They can be a real help for us in our daily routine. But they can also be misused and can be potentially very dangerous.

My personal opinion? Use a microwave oven, but use it sensibly and safely.


Sources
http://www.foodscience.csiro.au/micwave1.htm
http://www.ccohs.ca/oshanswers/phys_agents/microwave_ovens.html
http://www.gallawa.com/microtech/Ch3.html
http://www.thedietchannel.com/Microwave-Cooking-And-Food-Vitamins.htm