3: Infrared Heating

Question 1

Describe infrared heating.

Answer 1

Infrared energy is the EM radiation emitted by hot objects.

When food are exposed to IR radiation:
- The organic matters in food absorbs IR energy
- Intermolecular transition between energy levels occurs according to the types of chemical bonds present
- Heat is released

The heating is not dependent on air for transmission and more efficient than conventional surface heating because air absorbs very little IR energy.

Question 2

What are the factors that affects heat transfer of IR heating?

Answer 2

• Surface temperature of radiator and heated material (High temp produce short wavelength which increases depth of penetration)
• Surface properties of radiator and heated material
• Shape of radiator and heated material.

Question 3

What are black bodies and grey bodies?

Answer 3

• Black body refers to an ideal object that absorbs and emits all radiation at all wavelengths, it is a perfect absorber and emitter of radiation.
• Grey body is a real object that absorbs some radiation and reflects or transmits the rest. A grey body only emits a fraction of radiation it absorbs.

Question 4

What are the two types of reflection in food materials?

Answer 4

Surface reflection and body reflection due to scattering.

Question 5

What are the factors that affect IR absorption?

Answer 5

Water content, thickness, and physicochemical rpoperties

Question 6

How can IR heating be applied?

Answer 6

• Dry blanching: FIR is used to inactivate enzymes, low power intensity prevents products from cooking.
• Drying: IR drying does not require heating medium, but is only applicable to thin and flat products. This can be overcame by combination of hot air drying and IR.
• Peeling: Rapid IR heating causes drying of skin peel, under vacuum the skin cracks. By blowing compressed air, skin is loosened and the skin can be removed via mechanical means such as using a pinch roller.
• Pasteurization and sterilization
• Baking and Roasting

Question 7

What affects the rate of heat transfer during IR heating?

Answer 7

The emissivity and temperature of both radiator and food.

Question 8

What are the types of IR radiation?

Answer 8

• NIR, MIR and FIR
• MIR and FIR is the most suitable for thermal processing of food.