Generality
The microwave oven – or more simply “microwave” – is a kitchen appliance that heats and cooks food by exposing it to electromagnetic radiation .
This radiation causes the polar molecules of the food to rotate billions of times per second and collide with each other, producing thermal energy; this process is known as “dielectric heating”.
Microwave ovens cook foods quickly and efficiently, as they exert a completely uniform excitation (especially with reference to other methods) on all foods with a high water content (less so on denser foods with low humidity).
The first microwave oven was invented after the Second World War by Percy Spencer, who used the radar technology developed by the American nation during the conflict; not surprisingly, the first name of the microwave oven (1946) was “Radarange”.
The “Raytheon” (US company for the defense) then granted the license to use its patents for domestic use, introduced by WJ Tappan in the year 1955; however, the tools were still too big and above all expensive to be applied in home use. In 1967 the “Amana Corporation” introduced the first “microwave countertop” and its use quickly spread to commercial and home kitchens around the world.
Today, microwave ovens are widely used, especially for heating already cooked foods and for cooking a particular variety of foods. They are also useful for the quick melting of certain otherwise more demanding ingredients, such as butter and chocolateto melt (traditionally processed in a bain-marie ).
How does the microwave oven work?
Some of the molecules that make up food – in particular those of water, but also lipids and carbohydrates – tend to align themselves in the direction of any electric field present, a bit like the needle of a compass tends to align itself with the magnetic field of the earth. This characteristic is due to the fact that these molecules have one end with a positive electric charge and another with a negative charge; for this reason they are defined as polar or polarized molecules or electric dipoles.
An electric field is generated inside a microwave oven which reverses its direction a few billion times per second. Consequently, the polar molecules of food change their orientation several billion times per second; this movement generates a continuous collision between the adjacent molecules, with mutual transfer of motion. From here originates the diffused heat that allows food to be cooked up to a few centimeters deep.
Microwaves heat water more efficiently, but also fat, sugar and ice to a lesser extent.
Unlike conventional ovens, microwave ovens usually do not reach temperatures sufficient to sensibly trigger the Maillard reactions (see also: cooking sugars , cooking fats , cooking proteins ), therefore – for example – they are not suitable for the browning of toast and croutons. Some exceptions occur when the microwave oven is used to heat dough rich in oil or other very fatty products (such as lard or pancetta), which reach much higher temperatures than water. Alternatively, there are accessories with thin metal coatings which, by becoming quite hot, can toast the foods in contact with them.
Precisely because the temperatures necessary for frying , browning and roasting are rarely reached, microwave ovens play a rather limited role in the professional kitchen. However, microwave technology can be integrated with other types of cooking (eg pre-cooking intended for roasting); or, the ovens themselves can be manufactured by integrating them with other heat production systems (such as the grill); in the latter case we speak of combi ovens . Furthermore, certain more modern instruments may be part of the so-called “over-the-range” units, with built-in extractor hoods.
Microwave Oven on Amazon
This microwave oven has a 20 liter oven capacity, painted sheet metal cavity, 6 power levels, door opening with side handle and 245 mm diameter rotating plate.
Thanks to the Defrost programme, it is sufficient to select the weight of the food to be defrosted and the microwave oven will take care of everything: the result will be simply perfect.
By simply pressing a button, Start Express automatically sets the oven to optimum power for 30 seconds. Each time the button is pressed another 30 seconds are added to the cooking time. A very simple, intuitive and useful feature.
The Child Lock function prevents the oven from being started accidentally, especially by children. When the function is active, it can only be deactivated by an adult, thus ensuring excellent safety in the kitchen.
Excellent simplicity for extraordinary results. The easy touch controls allow you to choose the weight of the food to cook and the microwave will automatically choose the cooking time and power.
Heating efficiency
The microwave oven converts only a portion of its electrical power into microwave energy. It consumes an average of 1100 W of electricity to produce 700 W of microwave power, or an efficiency of 64%; the remaining 400 W remains dissipated as heat, mainly in the magnetron tube. Then, more power is used to drive the lamps, AC transformer, cooling fan, food turntable motor, and control circuitry.
Plastics for Microwave Ovens
Not all materials lend themselves to being placed in the microwave oven and many tend to react negatively, increasing the risk of breakage of the appliance, flammability, food contamination, etc.
Some plastic containers and food packaging, only recently released, are specifically designed to resist microwave radiation.
Symbol certifying the suitability of the container for microwave cooking
These products may say “microwave safe”, have a specific microwave symbol (three lines of waves, one above the other), or provide instructions for proper microwave use.
Any of these three possibilities is a guarantee that, when used in accordance with the recommendations provided, the product is suitable for microwave use.
There are also special containers , which allow the cooking of foods that are generally not suitable for the microwave. An example is given by whole eggs in their shells, which normally explode when cooked in a microwave oven; in this regard, there are double chamber containers which perform steam cooking: the lower chamber, containing water, generates the steam which rises through special holes in the upper chamber, containing the egg or other foods to be cooked. The upper chamber is specially shielded to prevent microwaves from passing through, thus protecting the food placed inside.
Benefits and Safety Features
First, for their standard operating mode, commercial microwave ovens use a built-in timer; when it runs out, the oven switches off.
Unlike traditional systems, microwave ovens cook food without heating themselves and the environment.
At the end of cooking, food and pans removed from the microwave rarely heat up more than 100°C. On the contrary, they are often colder than the food being processed: since the container is inert to the microwaves which instead directly heat the food, the container undergoes only an indirect effect and reduces the risk of injury for the operator.
Compared to cooking in the oven or frying, cooking in the microwave uses lower temperatures regardless of the formation of moleculescarcinogenic , to the benefit of food safety . Microwave radiation penetrates deeper than radiated or conducted heat and causes food to heat up in proportion to its water content.
Pre-heating food in the microwave before placing it on the grill or pan reduces the time needed to cook it and decreases the formation of carcinogenic elements . Unlike frying, microwaving does not allow acrylamide to form in potatoes ; however, it is only limitedly effective in reducing the concentrations of solanine in these tubers .
Characteristics of Microwave Heating
Microwave ovens are often used to reheat leftover food; however, if the safety temperature is not reached, the bacterial contamination can remain high, with a relative increase in the risk of contracting a foodborne illness (a characteristic common to all inadequate regeneration methods ).
Uneven heating of food may be due in part to the uneven distribution of energy within the microwave oven and in part due to different energy absorption rates in various parts of the food.
The first problem can be solved with a stirrer, or a kind of “fan” that reflects the microwaves in all parts of the oven, or from a revolving platform for the food. However, the latter can leave parts uncovered such as, for example, the center of the oven (which always receives an irregular distribution of energy). Dead spots and hot spots in a microwave oven can be identified by placing a moistened piece of thermal paper inside it. When wet paper is subjected to the radiation it becomes hot enough to release the dye, providing a visual representation of the microwaves in the total volume. If several layers of paper are arranged with enough distance between them, a three-dimensional map of space can be created. Many receipts and sales receipts are printed on thermal paper,
The second problem, on the other hand, is due to the composition of the foods and their geometry, and must be solved by the cook by arranging the food so that it absorbs energy uniformly. In some materials of low thermal conductivity, where the dielectric steadily increases with temperature, microwave heating can cause localized thermal runaway.
Because of this phenomenon, microwave ovens set at too high power levels can also begin to cook the edges of frozen foods during defrosting .
Another episode of uneven heating can be seen in baked goods containing berries , such as raisins or berries . In these foods, the berries (which are moist and high in sugar) absorb more energy than the surrounding dry bread and cannot dissipate heat due to the reduced thermal conductivity of the surrounding material. Often, this causes the berries to overheat compared to the rest of the food.
The “defrost” (or “defrost”) oven setting uses low power levels designed to allow time for the microwaves to act slowly and the heat to be conducted from the most sensitive parts to the least exposed.
In turntable ovens, uniform heating can be achieved by off-centering the food on the tray.
Microwave heating can also be purposely uneven. Some programs (particularly for cakes ) detect material diversity and selectively deposit energy; this capacity is exploited by using containers, or even only single susceptors , made of suitable materials.
Effects on Food and Nutrients
Comparative studies on microwave cooking define that, if used correctly, it does not affect the nutritional content of foods any more than conventional systems do; moreover, it boasts a greater tendency to preserve various micronutrients thanks to the reduction of the overall times of exposure to heat. However , cooking human milk at high temperatures in the microwave is contraindicated, due to the marked reduction in the activity of the typical immune factors of this food .
All forms of cooking destroy some nutrients and do so in relative quantities to certain variables; the most important are: how much water is used in cooking, for how long the food is cooked and at what temperature. Various nutrients are compromised mainly by leaching and thermal inactivation, which would make microwave cooking more suitable, given the shorter cooking times and the absence of a preserving liquid.
Like other heating methods, microwaving converts vitamin B12 ( cobalamin) from active to inactive. The percentage of inactivation depends once again on the temperature reached and on the cooking time. A boiled food reaches a maximum of 100°C, but in some cases, cooking in the microwave can go beyond this threshold with a consequent increase in the specific vitamin loss. However, even in this case, the higher reduction rate is partially compensated by the shorter cooking times.
In a study on the impairment of phenolic compounds , it was observed that when cooking broccoli , microwaving eliminated 74% or more of the total compounds, compared with 66% by boiling and 47% by steaming.; the experimental has been questioned for a long time by several other studies.
To minimize losses of phenolic compounds in potatoes, the microwave oven should be set to 500W.
Cooked in the microwave, spinach retains almost all the concentration of folate ; by comparison, about 77% of it is lost by leaching (dilution) in boiling.
Additionally, microwaved bacon has significantly lower levels of carcinogenic nitrosamines than conventionally cooked bacon.
On the other hand, steamed vegetables tend to retain more nutrientscompared to the same ones prepared in the microwave.
In containing the water -soluble vitamins folic acid , B1 ( thiamin ) and B2 ( riboflavin ), microwave bleaching is 3-4 times more effective than boiling water, with the sole exception of C (or ascorbic acid , of which 28.8% is lost in the microwave vs. 16% in the latter).
Use in cleaning kitchen sponges
Certain studies have observed the use of the microwave oven for cleaning suitably moistened NON-metallic household sponges.
A 2006 work found that passing wet sponges for two minutes in a microwave oven (at 1000 watt power) is able to remove 99% of the coliform bacteria E. coli and MS2 phages , while the spores of Bacillus cereus are were eliminated in 4 minutes.
The “sterilization” of the sponges in the microwave is therefore to be preferred over washing them in the dishwasher, during which temperatures are often not reached which are sufficient to guarantee the killing of microbes.
