What is microwave and its uses

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Author: Christine Gehle (Bachelor of Science in Nutritional Science)

Generally

In microwave ovens, electromagnetic radiation generates heat in the food. This process reduces the cooking time, while the surface temperature remains relatively low. Microwaves are an alternative to the → stove / oven when they are used to prepare smaller dishes (up to 500 g). By defrosting and regenerating food and dishes, the microwave oven can save both time and energy when used properly.

Designs

Microwave ovens are available in various designs. The place of installation is to be taken into account when making a purchase decision. A distinction is made between table-top devices, built-in devices, built-in devices and built-in devices. According to the Federal Statistical Office, 71.3% of German households owned a microwave in 2018 [1].

Figure 1: Microwave as a tabletop device

In addition to the simple microwave oven are Microwave combination devices available in the stores. These devices are a combination of an oven and a microwave. Depending on the manufacturer, they have top and bottom heat, convection or grill function.

Mode of action

Microwaves only heat organic substances; the higher the water content in a food, the faster it heats up.
The molecules in the food can be polarized by the electronic field, one end of the molecule is charged negatively, the other end positively (dipole formation)
The negative end of the molecule is attracted to the positive end of another molecule; the molecules start to spin. With constantly changing voltage (alternating voltage), the molecules try to change direction. The molecules rub against each other and frictional heat is generated (the food heats up from the inside).
Microwaves can penetrate the food up to 2.5 cm deep from all sides.
Due to the penetration of the waves, the food is particularly hot 2-3 cm below the surface, but it can still be cold in the middle of the food, as can the surface.
The heat is not supplied from the outside in as with conventional heat sources (→ stove, oven ...), but instead takes place through the electromagnetic waves in the food.
The properties of the electromagnetic waves are determined solely by their respective wavelengths.

Layout and function

Figure 2: Scheme of a microwave

The most important component in a microwave device is the magnetron (Fig. 2 [9]). The magnetron generates the electromagnetic waves under the influence of a magnetic field and guides them through a sheet metal channel (waveguide [7]) and the coupling pin (8) into the cooking space (3). The magnetron is supplied with high voltage via a transformer (11). The cooking space consists of a metal chamber that is closed on five sides and is accessible through a door on the front. The waves are reflected through the metallic walls. There is usually a turntable on the base plate (1) through which the food to be cooked is moved and heated more evenly. A certain distance must be maintained between the base plate and the turntable, this ensures that the food can also be heated from below. The reflector wing (5) also serves to distribute the waves evenly. The cooling fan (10) cools the magnetron and blows its heat loss into the cooking space to keep it dry.

Application and security

A microwave can be used to defrost food and to warm and reheat food and beverages. Smaller portions or plate dishes can also be cooked in the microwave. The water- and fat-saving preparation of fruit and vegetables means that few minerals and vitamins are leached out. Cooking in a microwave oven is therefore particularly suitable for the preparation of light foods.

In order to achieve the best result when using a microwave, the requirements of the respective food must be observed. The power level (wattage) should be adapted to the desired result.

The power levels of a microwave vary depending on the manufacturer, generalized the following statements can be made:

Max. 1000 wattsSuitable for particularly rapid heating of food and drinks. Danger Hot spots!
560-850 wattsThis performance level can be used for:
- cooking meat, vegetables or side dishes
- the heating of insensitive dishes
- roasting desiccated coconut or almond sticks
260-500 wattsThis performance level is particularly suitable for:
- the gentle cooking of meat
- heating sensitive food
180-250 wattsThe second lowest power level is suitable for:
- the melting of butter (250 g approx. 1-2 minutes)
- the dissolving of gelatine (dissolved → gelatine approx. 1 minute at 180 watts)
- Melting cake icing (chop 100 g chocolate into pieces beforehand; approx. 2 minutes at 250 watts)
- the continued cooking of stews
80-90 wattsThe lowest power level is particularly suitable for:
- Thawing delicate foods
- Sources of e.g. B. Rice pudding
- Fermenting yeast dough
- Keep warm

In general, the following notes should be observed:

Always place food covered in the microwave to prevent it from drying out
Pierce food with a firm shell, such as sausages, before cooking to prevent the food from bursting
Food should be spread out as flat as possible on the plate so that it cooks evenly and there are no results Hot spots. In the case of very liquid food, stir well before consumption and in the case of baby food, be sure to check the temperature!
Always place food in the center of the appliance, so it will cook more evenly.
Because of the relatively low temperatures that can be achieved in microwave ovens, they cannot be used for frying, baking, browning or crusting.
Cooking times that are too long dry out the food and make it taste bland.
The appliance must not be switched on when the cooking space is empty. Otherwise, the microwaves will be reflected back to the magnetron and may damage it.

Suitable dishes for the microwave (the microwaves can penetrate through these materials):

Fireproof (dishwasher safe) porcelain
→ glass
Ceramics
Heat-resistant → plastic (up to 180 ° C)

Unsuitable dishes for the microwave (these materials reflect the waves):

→ metal
Crockery with metal decor (gold or silver rim)
Aluminum foil
Unglazed clay pots, tightly screwed glasses or crockery with cracks can overheat and burst.

There are innumerable warnings about the avoidable dangerous radiation of the microwave. However, since these are not rays but waves and these are located in a closed space, according to current scientific knowledge, no health risk can be assumed (Federal Office for Radiation Protection).

Cleaning and care

In order to avoid major soiling in the microwave, you should follow the instructions of the respective manufacturer and cover the food while heating. All removable parts can usually be easily cleaned in the dishwasher. If the interior is dirty, wipe it off with a damp cloth. It is important that all components are properly used again after cleaning. Microwave combination devices can be cleaned like ovens (→ ovens), cleaning and care depends on the materials. Attention: Repairs to microwave devices should only be carried out by a specialist. If the seals, door or hinges are damaged, the device must no longer be used.


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Interesting links

Video by chemist Mai Thi Nguyen-Kim about the function of the microwave "How bad are microwaves?"
HEA - Professional Association for Efficient Energy Use e. V .: microwaves. Accessed on 08/08/2019

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[1] Federal Statistical Office: Equipping private households with electrical household and other appliances - Germany. Accessed on July 22, 2019
Professional group for efficient energy use e. V. (HEA) (Ed.): Microwaves. Accessed on November 24, 2015
AID (information service for consumer protection, nutrition, agriculture) (ed.): Kitchen and technology. Bonn 2005
Professional group for efficient energy use e. V. (HEA) (Ed.): The Blue Cookbook - Electric Cooking. 2011
Mehringer, S. (Ed.): Household technology. Munich 1977
Naumann, G. (Ed.): Food processing in the household. Bonn 2010
Wegner, G. E. (Ed.): Electrical household appliances. Munich / Heidelberg 2008
Schlieper, C. A. (Ed.): Learning field housekeeping. Hamburg 2009
Schuhmacher, W. (Ed.): Household technology. Cologne-Porz 1983

Detailed references



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