Microwaving food - Yay or Nay?

For today's Home Economics microteaching lesson, one of our classmates talked about different cooking methods and one of the alternative cooking methods that is commonly used nowadays is microwaving.
Some comments brought up by my classmates was that using smaller sized food items will ensure faster cooking and microwave cooking may not be 100% safe. I remember being taught in detail about the principles behind microwaves during my Food Science and Technology in NUS but I could not remember the exact details. So I did some searching on the internet and here's a good link for anyone who needs some fast facts about cooking using microwave: USDA Food Safety and Inspection Service.

Well I believe to most people microwaving would sound dangerous because it uses microwave radiation to cook the food. Just the sound of the word radiation brings about horrific images of nuclear bombs, Chernobyl Incident, Fukushima Nuclear Plant breakdown, etc. How can we even think of using such a technology on our food? Surely there must be residual radiation remaining on the food and consuming microwaved food will therefore inevitably cause cancer! And so on...

I believe this is a popular misconception that people usually have as they do not have the knowledge in physics to understand the principles behind microwaves. Well, let me attempt to provide a simple summary of microwaves:

What are microwaves?
Microwaves are radio waves that have a frequency of 2.45GHz or a wavelength of 122mm.
Ever wondered why the door of the microwave oven is made of one layer of clear glass with an inner layer of perforated material? Well, as long as the size of the holes are less than 122mm, microwaves cannot escape through the glass and you can still see your food when it is cooking in the oven.

How do they heat up food?
When microwaves are passed through the food item, dipolar molecules (molecules that has a positive and a negative moment) such as water, fats and some other food molecules, are forced to move continuously as they align themselves to the alternating electric field of the microwaves. These molecules move around in the media and therefore release heat energy in a process known as dielectric heating.

Are nutrients lost during microwaving?
Generally, microwaving does not destroy more nutrients in food as compared to conventional cooking methods because of the shorter cooking times employed. Of course, this will also depend on duration of microwaving, power used and amount of water used in the process.


What are the guidelines for microwaving? 

1. Microwaves will be more effective in food where the water is in the liquid state rather than the solid state as the water molecules will be mobile. 
2. Even distribution of water in the food will ensure even heating. 
3. Never heat homogeneous liquids in the microwave as this will the liquid to exceed its boiling point without boiling. Adding any dry solids to this super-heated liquid will then cause the liquid to start boiling explosively. 
4. Never use covered containers or enclosed food like eggs in the microwave oven. The build up of steam in the enclosed environment will cause it to explode. 
5. Do not use plastics. They will melt!
6. Do not use metals too. They conduct electricity and they will act as another heating element in the oven, causing uneven cooking. 
7. Give the food some "standing time" after microwaving so that the heat in the food can distribute. 

So to answer my classmate's question, no smaller pieces of food do not ensure that the food cook faster. The position of the food in the oven and how evenly the moisture in the food is distributed will be more crucial factors to consider to ensure quick and even heating in the microwave oven. 

And for the question of safety of microwaved food, the issues pertaining to the safety of the food does not lie with the possibility of "residual radioactivity", however, it lies on the time and temperature of the food. As the food is heated very quickly in the microwave oven, the general concern is that the food does not achieve the temperature and time required to kill the harmful bacteria in the food. 

Another concern is the presence of harmful chemicals such as acrylamide (lethal neurotoxin) and solanine (glycoalkaloid poison). Both are found in potatoes and microwaving potatoes do not produce acrylamide but it is not effective in reducing solanine levels in potatoes as compared to other methods like deep frying. 

So my answer is yes microwaves are safe BUT we do have to be careful when selecting the food and containers that we are using in the microwave oven. 

Hope this entry sheds some light on the common misconceptions of microwaves!