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Packaging for microwave processing of food


Key words Packaging, microwave heating, in-pack pasteurisation, optimised food packaging, active packaging, susceptor
Latest version 2010/12/22
Completed by SP

How does it work?

Primary objective To optimise in-pack heating, reheating or pasteurisation of food products by microwave processing.
Working principle Uniform heating by microwaves is affected by the package design and other factors such as food composition, geometry and oven design. Non-uniform heating with so called hot and cold spots is still encountered. These problems could be solved to a large extent through modelling based optimisation of the package (geometry, size, package compartments, etc.).

Microwave heating of packed foods may include heating while building up a pressure within the package. This principle is often used for microwave processing of packaged readymade meals, e.g. for pasteurisation in packages with a valve. In-pack pasteurisation is achieved by specially adapted trays, films and valves. The shape of the trays is optimised for uniform heating and they are sealed with plastic films including a valve. In other types of packages for microwave heating, different kinds of active packaging are used. For pizzas, pies etc., which are intended for microwave heating, susceptor packages are often used in order to achieve enough crispiness after microwave heating.

Additional effects Using in-pack pasteurisation recontamination can be avoided.

Microwave heating

Important process parameters Microwave power, heating time, pressure.
Important product parameters Package design: Size, geometry.

Product characteristics: Geometry, size of food components, composition of the food.

What can it be used for?

Products Microwave processing of packaged foods can be used for food applications such as pasteurisation of prepared foods, yoghurt, fresh pasta and packed bread.
Operations Heating and reheating processes as well as in-pack pasteurisation.
Solutions for short comings The technology makes it possible to heat packaged foods by direct heating, faster and often more energy efficient. This technology can replace or complement a conventional technology.

What can it NOT be used for?

Products Fat or oil based products may reach very high temperatures and this might be a restriction for the material.
Operations To achieve sterilisation temperatures, the equipment needs to be pressurized to avoid explosion of the package.
Other limitations
Risks or hazards The package material should be approved, proving that it does not release chemical components in contact with food products.


Maturity There are packages available, optimised for in-pack pasteurisation, heating and reheating of products.
Modularity /Implementation Microwave processing for pasteurisation of packaged foods can be inserted in an existing production line. An optimal package needs to be chosen for the specific application and the geometry, size and composition of the food product has to be optimized.
Consumer aspects Consumers are demanding higher quality products, easier-to-use-packaging and faster, more efficient cooking methods.
Legal aspects Food grade packaging is needed.
Environmental aspects Renewable material could be chosen.

Further Information

Institutes SP, CTCPA
Companies MicVac, NutriPack, The Guillin Group, Faerch Plast, Freshflex, Rockwell Solutions, Tops foods
References 1. Edwards, J. S. A. et al. (2006) Hospital food service: a comparative analysis of systems and introducing the “Steamplicity” concept. Journal of Human Nutrition and Dietetics ,19: 421-430.

2. Hartwell, H. J., Edwards, J. S. A. et al. (2007) Plate versus bulk trolley food service in a hospital: comparison of patients' satisfaction. Journal of Nutrition, 23(3): 211-218.

3. Ohlsson, T., Risman P. O. (1978) Temperature distribution of microwave heating - spheres and cylinders. Journal of Microwave Power, 13(4): 303-310.

4. Ramey, R. L.,Lewis, T. S. (1968) Properties of thin metal films at microwave frequencies. Journal of Applied Physics, 39(3): 1747-1752.

5. Sacharov, S., Schiffman, R. (1995) Microwave Packaging. Leatherhead, UK., Pira International.

6. Wäppling-Raaholt, B., Ohlsson T. (2005) Improving microwave heating uniformity in foods. M. Regier, Woodhead Publishing, Ltd.

7. Wäppling-Raaholt, B., Ohlsson, T. (2009) Influence of Food Geometry and Dielectric Properties on Heating Performance. Development of Products and Packages for microwave Ovens. P. Pescheck and M. Lorence, Woodhead Publishing: 42 pp.

8. Wäppling-Raaholt, B., T. Ohlsson, et al., Eds. (2007). Microwave Heating of Ready Meals – FDTD Simulation Tools for Improving the Heating Uniformity Advances in Microwave and Radio Frequency Processing. Berlin Heidelberg, Springer.

9. IEC (2002). IEC publication 60519-6 Safety in electroheat installations - Part 6: Specifications for safety in industrial microwave heating equipment. Ed. 2.0 b.

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Created by on 23 February 2011, at 13:20