7
HEATING CATEGORY
The heating category (a letter A to E) developed
by MAFF (Ministry of Agriculture, Fisheries and
Food) with microwave oven and food
manufacturers indicates the ability of the oven to
heat small quantities of food (up to 500g [1lb
2oz]). It does not represent the general
performance of the oven.
HOW YOUR OVEN WORKS
Microwaves are energy waves, similar to those
used for TV and radio signals.
Electrical energy is converted into microwave
energy, which is directed into the oven cavity via
a waveguide. To prevent food and grease entering
the wave guide it is protected by the waveguide
cover.
Microwaves cannot pass through metal, because
of this the oven cavity is made of metal and there
is a fine metal mesh on the door.
During cooking the microwaves bounce off the
sides of the oven cavity at random.
Microwaves will pass through certain materials,
such as glass and plastic, to heat the food.
(See ‘Suitable Cookware’ on page 37).
Water, sugar and fat in food absorb microwaves
which cause them to vibrate. This creates heat by
friction, in the same way your hands get warm
when you rub them together.
The outer areas of the food are heated by the
microwave energy, then the heat moves to the
centre by conduction, as it does in conventional
cooking. It is important to turn, rearrange or stir
food to ensure even heating.
Once cooking is complete, the oven
automatically stops producing microwaves.
Standing time is necessary after cooking, as it
enables the heat to disperse equally throughout
the food.
Microwave output power
in Watts (based on
international (IEC 60705)
standard).
600 700 800 900 1000 Watts
OVEN
OUTPUT
POWER
Less heating time required
More heating time required
OVEN
OUTPUT
CATEGORY
Less heating time required
More heating time required
Letter representing the
oven heating category.
Microwave Symbol.
A B C D E
Food packs carry cooking instructions for heating
categories A to E. Follow instructions for the
letter corresponding to the oven’s heating
category. The higher the output power and
heating category of the oven the less heating time
is required as shown opposite.
