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Baking with combined microwave and infrared/impingement heating

Identification

Key words Microwave, infrared, impingement, baking, heating, bread, cake, cookie, oven, crust, surface temperature
Latest version 2013/02/07
Completed by SP

How does it work?

Primary objective To reduce baking time and energy
Working principle In microwave baking, heat is generated internally by the interactions of microwaves with charged and polar molecules, mainly water, in the dough. The microwave energy is distributed throughout the product, and the oven is at ambient temperature. This is a fast and energy efficient process (4, 7, 9). However, microwave baking involves quality problems such as lack of crust formation, poor colour and flavour development, high moisture loss, low product height, firm texture and rapid staling (4, 7, 9). In a conventional oven, the product surface temperature is high. Moisture evaporates readily and a crust is formed where while colour and aroma are developed. During microwave heating, on the other hand, the product is heated internally and evaporation inside the dough creates a pressure-driven flow of liquid water and vapour towards the product surface. Due to the ambient oven temperature, evaporation is slow and accumulation of moisture on the surface gives a soggy appearance (1).

The problems encountered in microwave baking can be overcome by combining microwave with impingement or infrared (IR) baking (1, 5, 10). Impingement and IR heating act at different time and spatial locations relative to microwave heating. Therefore, both overall heating rate and the uniformity of heating can be improved (2). In impingement and IR (with short penetration depth) baking the product surface quickly gets hot which improves water evaporation and leads to immediate crust formation.

Images
Additional effects Microwave baking offers space savings, compared to conventional oven baking.
Important process parameters Process parameters : baking time, oven temperature, microwave heating power and wavelength, IR power and wavelength, IR emitter-to-product distance, impingement air temperature and velocity, impingement nozzle geometry, nozzle-to-product distance, jet orientation, microwave and IR/impingement process sequence.
Important product parameters Product parameters: structure, size and geometry, composition, moisture content, dielectric properties. Product formulation may need adaptation to the faster baking process achieved in microwave baking.

What can it be used for?

Products Bread, cakes, cookies and other baked products
Operations Baking
Solutions for short comings Conventional baking is a time- and energy- consuming process. Combining microwaves with impingement or IR baking provides for an efficient baking process with comparable results to that of conventional baking.

Microwave and IR heating provides flexible and precise process control, short start-up and shut-down times and avoids unnecessary heating of surrounding air. Better control of heat transport, moisture transport, and product porosity can be achieved (2, 7). With good control of the heat transport, the baking process can be designed to achieve specific product quality characteristics, for example thin/thick crust or crumb porosity.

What can it NOT be used for?

Products Microwave, IR, and impingement baking are fast methods. There might not be enough time for dough expansion and setting, or for reactions and interactions such as starch conversion and gelatinization that normally takes place during conventional baking. Microwaves may also affect components such as gluten and flavour components in different ways as for conventional heating. Therefore, dough or batter formulation needs to be adapted (7).
Operations Only baking has been considered in this technology sheet.
Other limitations The microwave heating process has to be properly designed to avoid hot spots.
Risks or hazards Observe safety regulations when using microwave and IR ovens. Exposure to microwave and IR radiation can produce heat damage and have chronic adverse effects on the eyes and skin. Observe normal safety regulations when working with hot ovens.

Implementation

Maturity Combination ovens are under development.
Modularity /Implementation Combined microwave and impingement/IR ovens can be inserted in an existing production line.
Consumer aspects Microwave heating is well accepted by consumers, as the majority of the households is equipped with a microwave.

IR heating has been used in the restaurant business for the last 25 years. However, consumers may be sceptic towards IR heating, as it sometimes is assumed to be the same as irradiation of foods, which may be regarded as negative due to assumed health effects (2,6). Impingement heating is a form of conventional convective heating, which has been used for long time and is well accepted.

Legal aspects Equipment using microwave source have to comply with the ISM bands and with regulation EN 55011:2009 (Industrial, scientific and medical equipment. Radio-frequency disturbance characteristics. Limits and methods of measurement) and CE marking.

IR equipment should comply with:

Directive 2006/25/EC of the European Parliament on the minimum health and safety requirements regarding the exposure of workers to risks arising from physical agents (artificial optical radiation) (19th individual directive within the meaning of article 16(1) of directive 89/391/EEC).

Directive 2004/40/EC exposure to electromagnetic fields (protection of workers)

Environmental aspects Combined microwave and impingement/IR baking uses less energy than conventional baking.

Further Information

Institutes SP, DIL, TTZ
Companies Ircon, Binar Elektronik, Buhler Aeroglide
References 1. Datta A.K., Ni H. 2002. Infrared and hot-air-assisted microwave heating of foods for control of surface moisture. Journal of Food Engineering 51, 355-364.

2. Datta A.K., Geedipalli S.S.R., Almeida M.F. 2005. Microwave combination heating. Food Technology 59(1), 36-40. 3. Demirekler P., Sumnu G., Sahin S. 2004. Optimization of bread baking in a halogen lamp-microwave combination oven by response surface methodology. European Food Research Technology 219, 341-347. 4. Demirkesen I., Sumnu G., Sahin S., Uysal N. 2011. International Journal of Food Science and Technology 46, 1809-1815. 5. Olsson E.E.M., Trägårdh A.C., Ahrné L.M. 2005. Effect of near-infrared radiation and jet impingement heat transfer on crust formation of bread. Journal of Food Science 70 (8), E484-E491. 6. Ovadia D.Z., Walker C.E. 1998. Impingement in food processing. Food Technology 52(4), 46-50. 7. Sumnu G. 2001. A review of microwave baking of foods. International Journal of Food Science and Technology 36, 117-127. 8. Sumnu G., Sahin S., Sevimli M. 2005. Microwave, infrared and infrared-microwave combination baking of cakes. Journal of Food Engineering 71, 150-155. 9. Sumnu G., Datta A.K., Sahin S., Keskin S.O., Rakesh V. 2007. Transport and related properties of breads baked using various heating modes. Journal of Food Engineering 78, 1382-1387. 10. Zhang J., Datta A.K. 2006. Mathematical modeling of bread baking process. Journal of Food Engineering 75, 78-89. 11. Wählby U., Skjöldebrand C., Junker E. 2000. Impact of impingement on cooking time and food quality. Journal of Food Engineering 43, 179-187.

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Created by Evelina.tiback on 7 February 2013, at 10:33