IR heating in food processing
August 2009
Temperature Measurement
Infrared heating is gaining momentum in food processing because it is fast, energy efficient, contact-free and uniform. It is successfully used in drying, roasting, baking and sterilisation applications, with optimum results sometimes obtained from a combination of convection and IR heating.
Food is primarily heated to enhance taste and to extend shelf life. IR heating is ideal since the radiation is readily absorbed by organic substances and generates heat. Heat transfer is fast and can be achieved over some distance with insignificant losses. The wavelength of IR emission can be varied to achieve different effects: penetration, colour, crust, etc. IR heaters are broadly classified as shortwave (0,78–1,4 micron), medium wave (1,5–3,0 micron) and long wave (3,0–6 micron).
The effect of wavelength
Different food components absorb IR energy better at different wavelengths. Choosing a heater of the appropriate wavelength allows users to selectively heat the required food component. Shortwave IR penetrates deeper whereas the longer wavelengths have a greater effect on surface layers. Water, sugars and proteins absorb infrared heat best at wavelengths between 2,5 and 3,3 micron – medium to long wave IR.
Typical applications include the following:
Drying and dehydration
A combination of IR heating and air convection offers better results than air drying alone. Similar improvements can be obtained by adding IR heating to freeze drying processes.
Drying of fruit and vegetables using this combination has resulted in reduced drying times, improved energy efficiency, reduced air-flow requirements, superior product quality and lower overall cost.
Broiling
Some shellfish are irradiated aggressively with shortwave IR to open them. Subsequently they are broiled in the shell with long wave IR, preserving the aroma and texture. Good results are also obtained when heating potatoes, meat products and fish. Depending on the intensity and wavelength of the IR various surface effects like crusts can be formed.
Roasting
Nuts, cocoa beans and similar products are roasted effectively and fast with IR with superior effects on the outer layers. Very fast throughput can also be achieved when heating pre-baked pizzas on a conveyor system.
Sterilisation
IR heating is used to destroy enzymes and micro-organisms such as spores, yeast and bacteria. A typical example is heating the exposed layer of foods in glass or cans prior to sealing of the container.
unitemp designs and manufactures infrared heating arrays, air heating systems and control panels. Drawing on 30 years’ experience, the company has implemented heating solutions for most of the applications mentioned above.
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