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Microwave Oven - Microwave Cooking

Generality

The microwave oven - or more simply "microwave" - ​​is a kitchen appliance that heats and cooks food through exposure to electromagnetic radiation.

These radiations cause the polar molecules of food to rotate billions of times per second and to collide with each other, producing thermal energy; this process is known as "dielectric heating".

Microwave ovens cook food quickly and efficiently, as they exert a completely uniform excitement (especially with reference to other methods) on all foods with a high water content (less on those that are denser and with poor 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 defense company) then granted the license to use its patents for domestic use, introduced by WJ Tappan in the year 1955; however, the instruments were still too large and above all expensive to be applied in home use. In 1967 the "Amana Corporation" introduced the first "microwave work plan" and its use spread rapidly in commercial kitchens and housewives around the world.

Today, microwave ovens are widely used, especially for heating cooked foods and for cooking a particular variety of foods. They are also useful for the rapid dissolution of certain otherwise more demanding ingredients, such as butter and chocolate to 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 line up in the direction of the electric field that may be present, much like the needle of a compass tends to align 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 polar or polarized molecules or electric dipoles are defined.

Inside an microwave oven an electric field is generated that reverses its direction a few billion times per second. As a result, the polar molecules of food change their orientation several billion times per second; this movement generates a continuous collision between the adjacent molecules, with reciprocal transfer of motion. From here originates the diffused heat that allows the cooking of food up to a few centimeters in depth.

Microwaves heat water more efficiently, but to a lesser extent also fats, sugars and ice.

Unlike conventional ovens, microwave ovens usually do not reach temperatures sufficient to significantly trigger Maillard reactions (see also: cook sugars, cook fat, cook proteins), then - for example - are not suitable for toasting toast and croutons. Some exceptions occur in cases where the microwave oven is used to heat mixtures rich in oil or other very fatty products (such as lard or pancetta), which reach temperatures far higher than those of water. Alternatively, there are accessories with thin metal coatings that, by becoming quite warm, can toast the foods that are in contact with them.

Precisely because of the fact that the temperatures required for frying, au gratin and roasting are rarely reached, in the professional kitchen microwave ovens play a rather limited role. However, the microwave technology can be integrated with other types of cooking (eg pre-cooking for roasting); or, the furnaces themselves can be manufactured by integration with other heat production systems (such as the grill); in the latter case we speak of combined ovens . Moreover, some more modern instruments can be part of the so-called "over-the-range" units, with built-in extractor hoods.

Heating efficiency

The microwave oven converts only part of its electrical supply into microwave energy. It consumes on average 1100 W of electricity for the production of 700 W of microwave power, or a yield of 64%; the remaining 400 W remain dissipated in the form of heat, especially in the magnetron tube. Then, more power is used to operate the lamps, the alternating current transformer, the cooling fan, the turntable motor for food and the control circuits.

5 Minute Pie - At the Microwave

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Microwave Oven Plastics

Not all materials lend themselves to being inserted in the microwave oven and many tend to react negatively, increasing the risk of breaking the appliance, inflammability, contamination of the food, etc.

Some plastic containers and food packaging, only recently distributed, are specifically designed to withstand microwave radiation.

Symbol that certifies the suitability of the container for microwave cooking

These products may mention the word "microwave safe", depict the specific microwave symbol (three lines of waves, one above the other), or provide instructions for proper use in the microwave.

Any of these three possibilities is the guarantee that, if used in accordance with the recommendations given, the product is suitable for use in the microwave.

There are also special containers, which allow cooking of foods generally unsuitable for microwaves. An example is given by whole eggs with shell, which normally explode when cooked inside the microwave oven; in this regard there are double-chamber containers that carry out steam cooking: the lower chamber, containing water, generates the steam that rises through special holes in the upper chamber, containing the egg or other foods to be cooked. The upper chamber is specially shielded so as not to let the microwaves pass through it, thus protecting the food inside it.

Benefits and Security Features

First of all, for the standard operating mode, commercial microwave ovens use a built-in timer; when it runs out, the oven turns off.

Unlike traditional systems, microwave ovens cook food without heating themselves and the environment.

At the end of cooking, the food and pots removed from the microwave oven 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 microwaves which instead directly heat the food, the container suffers only an indirect effect and reduces the risk of injury for the operator.

Compared to cooking in the oven or frying, microwave cooking uses lower temperatures regardless of the formation of carcinogenic molecules, to the benefit of food safety . The microwave radiation penetrates deeper than the radiated or conducted heat and heats the food in proportion to its water content.

Pre-heating food in the microwave before setting it on the grill or pan reduces the time needed to cook it and reduces the formation of carcinogens. Unlike frying, the microwave oven does not allow the formation of acrylamide in potatoes ; however, it is only slightly effective in reducing solanine concentrations in these tubers.

Features of Microwave Heating

Microwave ovens are often used to heat food scraps; however, if the safety temperature is not reached, bacterial contamination can remain high, with a relative increase in the risk of contracting a foodborne illness (a feature common to all inadequate regeneration methods).

Uneven heating of the food may be due in part to the uneven distribution of the energy inside the microwave oven and, in part, due to the different energy absorption rates in various parts of the food.

The first problem can be solved with a stirrer, that is a kind of "fan" that reflects the microwaves in all the parts of the oven, or from a revolving platform for food. However, the latter can leave parts uncovered such as, for example, the center of the oven (which always receives an uneven distribution of energy). Dead spots and hot spots in a microwave oven can be found by placing a piece of dampened thermal paper inside. When the wet paper is subjected to 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 sufficient distance between them, a three-dimensional map of the space can be created. Many receipts and sales receipts are printed on thermal paper, which makes this operation simple to invoice.

The second problem is instead 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 the energy uniformly. In some materials with low thermal conductivity, where the dielectric increases constantly at temperature, microwave heating can cause localized thermal instability.

Because of this phenomenon, microwave ovens calibrated with too high power levels can also begin to cook the edges of frozen food during thawing.

Another episode of irregular heating can be observed in baked products containing berries, such as raisins or berries. In these foods, the berries (which are moist and rich in sugars) 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 setting of the "defrost" (or "defrost") oven uses low power levels designed to allow time for microwaves to act slowly and the heat to be led by the parts most sensitive to the least exposed ones.

In ovens with a turntable, uniform heating can be achieved by offsetting the food on the tray.

Microwave heating can also be specially irregular. Some programs (in particular for cakes) identify the diversity of materials and deposit energy selectively; this capacity is exploited by using containers, or even just individual susceptors, made of special materials.

Effects on food and nutrients

Comparative studies on microwave cooking define that, if used correctly, this does not affect the nutritional content of food more than conventional systems do; moreover, it has a greater tendency to conserve various micronutrients thanks to the reduction in overall exposure times to heat. The cooking of human milk at high temperatures in the microwave is however contraindicated, due to the marked reduction in the activity of the immune factors typical of this food.

All forms of cooking destroy certain nutrients and do so in quantities relative to certain variables; the most important are: how much water is used in cooking, how long the food is cooked and at what temperature. Various nutrients are compromised above all due to leaching and thermal inactivation, which would make the microwave cooking more suitable, given the shorter cooking times and the absence of a liquid.

Like other methods of heating, the microwave one converts vitamin B12 ( cobalamin ) from active to inactive. The inactivation percentage again depends on the temperature reached and the cooking time. A boiled food reaches a maximum of 100 ° C, but in some cases, microwave cooking can exceed this threshold with a consequent increase in specific vitamin loss. However, even in this case, the higher rate of curtailment is partially offset by the shorter cooking times.

In a study on the impairment of phenolic compounds, it was observed that, when broccoli is cooked, the microwave oven eliminates 74% or more of the total compounds, compared to 66% of boiling and 47% of steam cooking; the experimental has been long questioned 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 folates ; in comparison, about 77% are lost in boiling due to leaching (dilution).

Furthermore, microwaved pancetta has significantly lower levels of carcinogenic nitrosamines than those cooked conventionally.

On the other hand, steamed vegetables tend to retain more nutrients than microwaves.

In containing the water-soluble folic acid, B1 ( thiamine ) and B2 ( riboflavin ) vitamins, microwave bleaching is 3-4 times more effective than that performed in boiling water, with the sole exception of C (or ascorbic acid, of which 28.8% is lost in the microwave vs. 16% of the latter).

Use in Cleaning Kitchen Sponges

Certain studies have observed the use of the microwave oven for the cleaning of NON metallic appropriately dampened sponges.

A work in 2006 found that the passage of 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 been eliminated in 4 minutes.

The "sterilization" of sponges in microwaves is therefore to be preferred over the washing of the same in dishwashers, during which often sufficient temperatures are not reached to guarantee the killing of microbes.