English
- En-7 -
Microwaves and How They Work
Microwaves are a form of high frequency electromagnetic
waves (app. 12 cm wave length) similar to those used by a
radio.
Electricity is converted into microwave energy by the
magnetron tube. The microwaves travel from the magnetron
tube to the oven cavity where they are reflected, transmitted
or absorbed.
Reflection
Microwaves are reflected by metal
just as a ball is bounced off a wall.
A combination of stationary (interior
walls) and rotating metal (turntable
or stirrer fan) helps assure that the
microwaves are well distributed
within the oven cavity produce even
cooking.
Transmission
Microwaves pass through some
materials such as paper, glass and
plastic much like sunlight shining
through a window. Because these
substances do not absorb or reflect
the microwave energy, they are
ideal materials for microwave oven
cooking containers.
Absorption
Microwaves are absorbed by food.
They penetrate to a depth of about
2-4 cm. Microwave energy excites
the molecules in the food (especially
water, fat and sugar molecules), and
causes them to vibrate very quickly.
The vibration causes friction and
heat is produced. In large foods, the
heat which is produced by friction is conducted to the center
to finish cooking the food.
Utensil Guide
Food Characteristics
FOOD CHARACTERISTICS
Food characteristics which affect conventional cooking are
more pronounced with microwave heating.
Size
–– Small portions cook faster than large ones.
Shape
–– Uniform sizes
heat more evenly. To
compensate for
irregular shapes, place
thin pieces toward the
centre of the dish and
thicker pieces toward
the edge of dish.
Starting Temperatures
–– Room temperature foods take
less time to heat up than refrigerator frozen foods.
Bone and Fat
–– Both
affect heating. Bones
may cause irregular
heating. Large amounts
of fat absorb microwave
energy and meat next
to these areas may
overcook.
Density
–– Porous, airy foods take less time to heat than
heavy, compact foods.
Microwave
Aluminum foil
No
Glass tray
Yes
Browning dish
Yes
Dinnerware:
Oven/Microwave safe
Non-Oven/Microwave
safe
Yes
No
Disposable polyester/Paperboard dishes
Yes
Glassware:
Oven glassware & ceramic
Non-heat
resistant
Yes
No
Metal cookware
No
Metal twist-ties
No
Paper towels and napkins
Yes
Plastic dishes: Microwave safe
Non Microwave safe
Yes
No
Microwave safe plastic wrap
Yes
Straw, Wicker, Wood
Yes
Thermometers: Microwave safe
Conventional
Yes
No
Grease proof paper
Yes
