Methods of heat transfer

1. Basic Cooking Principles
Chef Mehernosh Dhanda
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2. Scope
After this session you will be able to:
 Know what is heat
 How heat is transferred to foods
 What is the effect of heat on different constituents of
food
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3. What is Heat?
 Heat is a type of energy.
 When the food item is heated, the molecules absorb
this energy they vibrate rapidly, expand & bounce
off each other causing the transmission of heat.
 The faster the molecules move, the higher is the
temperature.
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4. Heat Transfer
Transmission of heat occurs by:
 Conduction
 Convection
 Natural
 Mechanical
 Radiation
 Infrared
 Microwave
• Induction
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5. Conduction
 The movement of heat from one item to another with
direct contact.
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6. Convection
The transfer of heat through a medium (liquid/ gaseous)
There are two types of convection, namely
 Natural
 Mechanical
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7. Natural convection
 Natural convection occurs due to the tendency of
warm liquids/gasses to rise upwards while cooler
ones fall
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8. Mechanical convection
 Mechanical convection requires a fan or stirring
action to circulate heat quickly & evenly.
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9. Radiation
Radiation method does not require physical contact
between the heat source & the food, instead the heat
energy is transferred by waves of heat or light which
strike the food
There are two types of radiation heat transfer, namely
 Infrared
 Microwave
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10. Infrared radiation
Infrared radiation uses high temperature electric/heat
sources which transfer the energy as radiant heat to
the food. Eg: The coils of an electric toaster
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11. Microwave radiation
Microwave radiation uses high frequency waves
which penetrate inside the food & agitate the water
molecules , causing friction which in turn increases
the temperature & results in cooking
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12. Induction
 Induction heating is the
process of heating an
electrically conducting object
(usually a metal)
by electromagnetic
induction
 Heat is generated directly in
the pot or pan (cooking
vessel), as opposed to being
generated in the stovetop by
electrical coils or burning gas
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13. Effects of Heat on Foods
 Carbohydrates
 Fruit and vegetable fiber
 Proteins
 Fats
 Minerals, vitamins, pigment, and flavor components
 Water
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14.  Proteins coagulate
 Starches gelatinize
 Sugars caramelize
 Water evaporates
 Fats melt
 Fiber is softened
 Vitamins and pigments can be destroyed
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15. Cooking Times
 Consider:
 The cooking temperature
 The different speeds of heat transfer
 The size, temperature, and individual characteristics of
the food
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16. Group assignment
Prepare a word document of 500 words on any of the
following topics:
1. Green fuels/Eco friendly fuels for commercial food
preparation (e.g. Solar cooking)
2. Conserving energy costs in a commercial hotel kitchen
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17. Thank You
Sir, didn’t you have a full-faced
beard 3 seconds ago?
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