En-2
Moisture
content
Many fresh foods
e.g. vegetables
and fruit, vary in
moisture content
throughout the
season. Jacket
potatoes are a
particular
example of this. For this reason cooking times
may have to be adjusted throughout the year.
Dry ingredients e.g. rice, pasta, can dry out
further during storage and cooking times may
differ from ingredients freshly purchased.
Piercing
The skin or
membrane on
some foods will
cause steam to
build up during
cooking. These
foods must be
pierced or a strip
of skin should be
peeled off before cooking to allow the steam to
escape. Eggs, potatoes, apples, sausages etc,
will all need to be pierced before cooking. DO
NOT ATTEMPT TO BOIL EGGS IN THEIR
SHELLS.
General guidelines
Cooking with microwave energy
Microwaves are a form of high frequency
electromagnetic waves similar to those used in
radios. Electricity is converted into microwave
energy by a magnetron tube. The microwaves
travel from a magnetron tube to the oven
cavity where they are reflected, transmitted or
absorbed.
Reflection
Microwaves are reflected by metal similar to the
way a ball would bounce off a wall. Most metal
cookware and utensils are not recommended
for microwave cooking, since they would
produce uneven cooking. Also, if a metal dish is
placed close to the oven wall (which is also
metal), arcing (bluish sparks) could occur.
Arcing can damage an oven or cause a fire.
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 cooking containers. However, they
will get hot during cooking, because as food
cooks, heat is conducted from the food to the
dish.
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 is conducted to the centre to finish
cooking the food.
