Types of Heat Transfer

1. TYPES OF HEAT TRANSFER
To cook food up to desired texture & taste, heat must be
transferred from it’s source (gas flame or electric element) to food.
Understanding the ways & speed which transfer the heat, that
helps the chef to control the cooking process.
Heat is transferred in 3 different ways:
1.CONDUCTION
2.CONVECTION
3.RADIATION
In the next slide, we will discuss, all 3 methods in detail

2. CONDUCTION
When heat moves from its source & heats an item by touching
e.g. electricity flows through a wire the same way.
CONDUCTION OCCURS IN 2 WAYS
1.When heat moves from one item to other item by touching e.g.
gas flame heat a fry pan when placed on top of burner
2.When heat moves from one part of an item to an adjacent part o
the same item e.g. heat moves from pan bottom to handle
DIFFERENT MATERIALS CONDUCT HEAT AT DIFFERENT SPEEDS
Heat moves rapidly through copper & aluminum
Heat moves slowly in glass, stainless steel & porcelain.

3. CONVECTION
When heat moves by the movement of air, liquid or steam, the
movement of heat or convection is classified in 2 types:
1. NATURAL CONVECTION:
It occurs naturally when heat is applied to liquid, air, warmer ones
rise & cooler ones sink, it causes constant natural heat circulation
2. MECHANICAL CONVECTION:
It refers to movement of heat by artificial mechanical action e.g.
using a fan or stirring to circulate the heat

4. RADIATION
Unlike conduction & convection, radiation does not require
physical contact between heat source & food to be cooked.
Instead, heat is transferred by waves of heat.
The waves themselves are not actually heat energy, they are
changed into heat when they strike food.
Light waves, radio waves, X-rays are examples of radiation
not used for cooking.
The two kinds of radiation are used in kitchen, they are
discussed in next slide.

5. INFRARED RADIATION
This method uses an electrical coil, which is heated to very
high temperature, as a result it releases heat, that cook the food
Few examples of equipments which releases radiant heat:
toasters, salamander & glowing charcoal also considered.
MICROWAVE RADIATION
This method uses a special oven, which agitates the natural
water molecules present in the food & creates heat.
The heat is then spread by conduction & convection method
& cook the food

6. MUST REMEMBER WHEN USING MICROWAVE
Microwave cooking affects food containing water only, any
waterless material (e.g. plate) will not get hot.
But heat felt in a plate when cooking food in microwave, that
result from heat being conducted from food to the plate.
Microwave cooking requires certain types of utensils, such
as ceramic, heat resistant glass or microwaveable plastic.
Never use aluminum or stainless steel inside the microwave,
because metal prevent microwaves & also damage the oven.