Are microwave ovens used in the right way?

Dagbjørn Skipnes checks the use of an infrared camera to measure temperature distribution in a microwave oven
Microwaves heat food much faster than conventional cooking on the stove. As the heating time is shorter, achieving better quality of the food is also possible, claims Nofima Scientist Dagbjørn Skipnes Nofima, who has extensive experience with various heating methods of food.

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Dagbjørn Skipnes

Senior Scientist
Phone: +47 926 92 252
dagbjorn.skipnes@nofima.no

Dagbjørn Skipnes checks the use of an infrared camera to measure temperature distribution in a microwave oven
Dagbjørn Skipnes checks the use of an infrared camera to measure temperature distribution in a microwave oven

Microwaves heat food much faster than conventional cooking on the stove. As the heating time is shorter, achieving better quality of the food is also possible, claims Nofima Scientist Dagbjørn Skipnes Nofima, who has extensive experience with various heating methods of food.

But it is not certain that everyone perceives a meal heated in a microwave oven is a quality product. There may be several reasons for this, but part of the reason may be unfortunate use of the ovens.

Can it really be possible to destroy the food in a microwave – isn’t using a microwave oven something everyone can do?

Too much use of maximum power

“A typical problem with microwave ovens is that the user sets the oven to maximum power without taking into account the quantity, placement or cooking time. If you are going to make a product in a microwave, where the focus is on good quality and high nutritional content, there are many parameters you need to consider – and in this case full speed and high heat are rarely the best solution,” says Skipnes.

This means that both the producer and the person preparing the food must do this in a proper and correct manner.

Fresh ingredients of good quality

Firstly, you need to assume that the ingredients are fresh and of good quality. Secondly, the manufacturer must choose a packaging material and package design that is suitable for heating in the microwave. The material shall enable the microwaves to pass through it, and strive for the heating to be as even as possible.

As the microwaves penetrate into the food, actually up to several centimetres, it is possible to achieve more even distribution of heat in a food product than with heat penetrating from the outside. With incorrect use, it is easy to burn the edges, corners or even the centre of, for instance, a sausage. Part of the “corner effect” is now removed by the rotating glass plate at the bottom of the oven or rotating reflectors where the microwaves enter the oven. In order to obtain the most even distribution of heat in microwave heating, a round or oval-shaped packaging is also used.

Different foods need different heating times

Food with different properties, such as water content or salt concentration, need to be heated differently. Consequently, in certain cases, the placement of the food in the package is of importance for whether the whole meal is heated evenly. In some cases the temperature in a package can become very high if it is put in the microwave oven without considering the length of the heating time. If the temperature exceeds the stipulated maximum temperature for the packaging material, unfavourable substances may be transferred from the packaging to the food.

Burning can occur with any type of heating, but with microwaves it happens much faster. It is therefore important that producers of food to be heated in microwave ovens know how much heat is transferred to the product in the oven, and that simple and accurate heating guidelines are printed on the packaging. When food producers prepare these guidelines, it is important that the producers have carried out experiments involving different types of microwave ovens at different levels of power.

So it is up to the user to read the guidelines on the package. For example, heating for one minute at a moderate strength, then leaving the food to rest (read heat distribution) for one minute, followed by an additional minute at moderate strength could provide a good and even heating. At the same time, prime quality of the raw materials is retained.

Microwaves and packaging evolving

There are currently many exciting developments in the use of microwaves for heating food. Nofima has worked on a concept for fresh raw materials that are distributed packed in cold chain and are only heated once by microwave heating. There are examples of something similar for entire hospital dinners (Ullevål Hospital).

A lot is also happening on the packaging front. Today’s second and third generation packaging contains different types of valves / aeration or differentiated packaging material that allows heat through only in certain areas. In this way, different chambers of the pack may be heated individually. Moreover, microwave ovens are becoming more refined with better regulators and the ovens are becoming steadily easier to operate. Not least, we see that new technology has made it possible to produce large industrial microwave tunnels.

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