Microwaves and How They Work
– 3 –
Microwaves are a form of high frequency radio waves
similar to those used by a radio, including AM, FM
and CB. They are similar to a television where the
radio waves are converted to a picture on the screen.
However, microwaves are much shorter than radio
waves; approximately twelve centimetres wave
length. Electricity is converted into microwave energy
by the magnetron tube (which is the heart of the
microwave oven).
The microwaves are converted to heat in the food.
The microwaves enter from the outside of the food and
travel through the food losing half of their power every
two to three centimetres. Continued cooking to the centre
occurs by conduction.
Although pacemakers used to be affected by
microwaves (as well as by other radio waves), they
are now shielded and are not bothered by these
interferences. This allows people with pacemakers to
sit calmly by their radio or television and cook with
microwave ovens.
When microwaves come in contact with a substance,
any one or combination of three things may occur.
They can be:
1. REFLECTED
2. TRANSMITTED
3. ABSORBED
Reflection:
Metal substances REFLECT microwave energy and
because there is no absorption, there is no heating.
This is why the oven interior is either stainless steel
or epoxy-coated steel. This ensures that the
microwaves are kept inside the cavity and evenly
distributed throughout the food.
Transmission:
Such substances as paper, glass and plastic
TRANSMIT microwave energy and do not become
hot except from food. Because these substances do
not reflect or absorb microwave energy, they are
ideal materials for microwave cooking containers.
Absorption:
Food contains moisture and will ABSORB
microwave energy, which causes the moisture
molecules within the food to vibrate at an incredible
rate (2,450,000,000 times per second). Friction,
created by the vibration, produces heat energy which
is conducted throughout the food.
It is important to use the correct container when
cooking in a microwave oven. The following will help
you make the right selection.
How to Test a Container for Safe
Microwave Oven Use
TO TEST A CONTAINER FOR SAFE MICROWAVE
OVEN USE:
Fill a 1-cup glass measure with cool
water and place it in the microwave oven alongside
the empty container to be tested;
heat one (1)
minute at High Power
. If the container is
microwave oven-safe (transparent to microwave
energy), the container should remain comfortably
cool, the water in glass measure should be hot. If
the container is hot, it has absorbed some
microwave energy and should NOT be used. This
test cannot be used for plastic containers.
Paper Products and Freezer Wrap
Waxed paper, paper plates, cups and napkins
should not be used for heating or cooking food.
Freezer wrap should not be used as it is not heat
resistant and may melt. Paper towel, greaseproof
paper and bake paper may be safely used for short
periods of time for covering or lining.
Jars and Bottles
Jars and bottles can be used to warm food to serving
temperature, if the lid is removed first. Cooking should
not be done in these containers since most are not
heat resistant and during extended heating times,
heat from food would cause cracking or breaking.
Glass, Ceramic and China
Heat-Resistant glass cookware
is invaluable in
microwave cooking. Many of these items are readily
available in most homes: glass jugs, mixing bowls, loaf
dishes, covered casseroles, oblong baking dishes, pie
plates and round or square cake dishes. Examples of
this type of cookware are Pyrex® and Corningware®.
Dinnerware
can be used for microwave heating.
Many brands of dinnerware are microwave safe.
Check the care information for reference to microwave
use for dinnerware and serving pieces. If dinnerware is
marked ovenproof, it frequently is safe to use in the
microwave oven. However, to be sure, check by
conducting microwave dish test.
Several types of glassware and dinnerware
are not
recommended for use in the microwave oven. Do not
use dishes with metallic trim or containers with metal
parts. Do not use cups or mugs with glued on handles,
as they may fall off with continued heating. Do not use
delicate glassware. Although the glassware may be
transparent to microwave energy the heat from the
food may cause the glassware to crack.
Straw, Wicker and Wood
Straw and wicker baskets may be used in the
microwave oven for short periods of time to warm
rolls or bread. Large wooden utensils, such as bowls
or cutting boards should NOT be used for prolonged
heating as the microwave energy may cause the
wood to become dry and brittle.
Cookware and Utensils Guide
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