Baking by Infrared Radiation

Three modes of heat transfer are used in baking biscuits: radiation, conduction and convection. The most important is infrared radiation, which has the following advantages:

  • Penetrative heat transfer: Infrared radiation penetrates biscuit doughs by approximately 4mm, (depending on wavelength and moisture content). It is the only heat transfer mode to truly bake the product from the centre. This is the key advantage of baking by infrared radiation.
  • Biscuit structure: because radiation penetrates the dough pieces, it is essential to achieving good structure with optimum volume and texture and is always the main mode of heat transfer in the first part of the baking process.
  • Even moisture content:  baking with infrared radiation ensures a low moisture gradient from centre to the outer surface of the biscuit. It is the best heat transfer mode to avoid “checking” (cracks appearing in the biscuit after baking).
  • Efficiency: heating of the surrounding air in the baking chamber is not necessary, which lowers energy consumption.
  • Colouring: infrared radiation enables highlighted colour contrasts for crackers and rotary moulded products, whereas convection gives an overall, bland, even colour.
  • Versatile: infrared radiation baking is suitable for all types of biscuit.

Baker Pacific Multi-Purpose Oven Baking by Infrared Radiation

Heat Transfer Modes

Radiation

All objects above a temperature of absolute zero radiate energy to their surroundings. This energy or radiation is emitted as electromagnetic waves which travel at the speed of light. The waves may travel through a vacuum or other medium. When they impact an object, they are partially absorbed and partially reflected. Good emitters are also good absorbers of thermal radiation.

Infra-red radiation is in the wavelength band of 0.7-300 microns (above visible light). Higher temperatures produce shorter wave lengths. Typical wavelengths in a radiant oven are around 4.6 – 6.4 microns, which provides good heat penetration of the dough pieces.

Infrared radiation for baking is emitted principally by the DGF burner flames and by the radiant tubes in an Indirect Radiant oven.

Since the radiant energy is proportional to the temperature to the power of 4, a small increase in temperature will give a large increase in radiation. This contributes to the fast response of DGF ovens and their high efficiency.

Zone Diagrams for DGF Oven and Indirect Radiant Oven

Conduction

Conduction transfers heat from the oven band directly to the base of the dough pieces. The heat transfer is dependent on the temperature and heat mass of the oven band and the surface area of the band in contact with the dough piece. With steel bands and heavy mesh bands this approximates to full contact and is very effective.

Ovens with band pre-heat can quickly transfer heat into the base of the dough pieces and achieve rapid development of the biscuit structure and texture; this is particularly valuable for cracker baking.

Cracker Baking Oven with Band Pre-heat Burners below the Return Band Circuit

Convection

Convection baking uses hot air jets which impinge directly on the top of the dough pieces and the underside of the oven band. This system effectively dries and colours the surface of the dough pieces. However it produces a hard, dry skin on the dough pieces and will prevent good expansion and “lift” of the product if used at the start of the baking process. Also it is a cause of a moisture gradient between the surface (very dry) and the centre of the biscuit (more moist). This may result in “checking”, (cracking of biscuits after baking), unless the moisture gradient is reduced after baking.

Infrared Radiant Ovens

Direct Gas Fired Ovens

DGF ovens bake with infrared radiation. High rate burners enable rapid baking of crackers with excellent “lift”, open and flaky texture. For cracker baking pre-heat burners also increase conduction to the dough pieces in the first oven zone.

Eratec high rate infrared radiant burners with gas/air mixer and Siemens solenoid valve / zero governor in a Baker Pacific cracker oven

Indirect Radiant Oven

Baking is by infrared radiation from the hot radiant tubes above and below the baking band. The heating system is essentially a closed system and the energy required from the burner is only sufficient to maintain the baking temperature.

The burner draws in air for combustion and the excess is exhausted by a natural flue. This hot air / burnt gas in the flue can be used in a heat recovery system and this ensures a high efficiency.

Heat exchanger and radiant tubes installed in a baking chamber

Oven design and manufacture

Baker Pacific oven designs are based on extensive technical experience, heat transfer principles and test data from oven installations. Our ovens are now manufactured in China, using the highest quality materials and imported components. Our partners for manufacture and assembly are Dingson Food Machinery Ltd. www.dsm-mc.com

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