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2 Description 3 Hazards and controversy |
The idea for using microwaves to cook food was discovered by Percy Spencer who was working for Raytheon and was building magnetrons for radar sets. One day he was working on an active radar set when he had noticed a sudden and strange sensation, and saw that a chocolate bar he had in his pocket had melted. The holder of 120 patents, Percy was no stranger to discovery and experiment, and realized what was happening. The first food to be deliberately cooked with microwaves was popcorn, and the second was an egg (which exploded in the face of one of the experimenters).
In 1946 Raytheon patented the microwave cooking process and in 1947, they built the first commercial microwave oven, the Radarange. It was almost 6 feet (1.8 m) tall and weighed 750 pounds (340 kg). It was water-cooled and produced 3000 watts, about three times the amount of radiation produced by microwave ovens today. This first step was so successful that Raytheon eventually purchased Amana to round-out a complete home appliance product suite.
A number of other companies joined in the market, and for a time most systems were built by defense contractors, who were the most familiar with the magnetron. Litton was particularly well known in the restaurant business. By the early 1970s the technology had improved to the point where prices were falling rapidly. Formerly found only in large industrial applications, microwaves were increasingly becoming a standard fixture of most (western) kitchens. The rapidly falling price of microprocessors also helped by adding electronic controls to make the ovens easier to use. By the 1980s they were almost universal.
A microwave oven consists of:
The cooking chamber itself is a Faraday cage enclosure to prevent the microwaves escaping into the surroundings. The oven door is usually a glass panel, but has a layer of conductive mesh to maintain the shielding. Since the mesh width is much less than the wavelength of 12 cm, the microwave radiation can not pass the door, while light (with a much shorter wavelength) can.
Commercial chefs generally find microwave ovens to be of limited usefulness. See Microwaving for a discussion of this reason.
1. Uneven heating
Food is heated for so short a time and often cooked unevenly. Microwave ovens are frequently used for reheating previously cooked food, and bacterial contamination may not be killed by the reheating, resulting in food poisoning. The uneven heating is partly due to the uneven distribution of microwave energy inside the oven, and partly due to the different rates of energy absorption in different parts of the food. The first problem is reduced by a stirrer, a type of fan that reflects microwave energy to different parts of the oven as it rotates, and by a turntable that turns the food. The second problem must be addressed by the cook, who should arrange the food so that it absorbs energy evenly, and periodically test and shield any parts of the food that overheat.
2. Baby milk
Young Families, the Minnesota Extension Service of the University of Minnesota, warned in 1989; "''[microwave ovens] are not recommended for heating a baby's bottle. The bottle may seem cool to the touch, but the liquid inside may become extremely hot and could burn the baby's mouth and throat.
Also, the buildup of steam in a closed container, such as a baby bottle, could cause it to explode. Heating the bottle in a microwave can cause slight changes in the milk. In infant formulas, there may be a loss of some vitamins.
In expressed breast milk, some protective properties may be destroyed. Warming a bottle by holding it under tap water, or by setting it in a bowl of warm water, then testing it on your wrist before feeding may take a few minutes longer, but it is much safer." ''"
Dr. Lita Lee reported in British medical journal The Lancet (December 9, 1989) "Microwaving baby formulas converted certain trans-amino acids into their synthetic cis-isomers. Synthetic isomers, whether cis-amino acids or trans-fatty acids, are not biologically active. Further, one of the amino acids, L-proline, was converted to its d-isomer, which is known to be neurotoxic (poisonous to the nervous system) and nephrotoxic (poisonous to the kidneys). It's bad enough that many babies are not nursed, but now they are given fake milk (baby formula) made even more toxic via microwaving."
3. Medical use
An Oklahoma lawsuit in 1991 related to a hospital using a microwave oven to warm blood needed in a transfusion. A hip surgery patient, Norma Levitt, died from a blood transfusion after a nurse had warmed the blood in a microwave oven.
4. Scientific studies
In Comparative Study of Food Prepared Conventionally and in the Microwave Oven, Raum & Zelt 1992 report: "''Microwaved food contains both molecules and energies not present in food cooked in the way humans have been cooking food since the discovery of fire. . .
''. . . Naturally occurring amino acids have been observed to undergo isomeric changes (changes in shape morphing) as well as transformation into toxic forms, under the impact of microwaves produced in ovens.
''One short-term study found significant and disturbing changes in the blood of individuals consuming microwaved milk and vegetables. Eight volunteers ate various combinations of the same foods cooked different ways.
''All foods that were processed through the microwave ovens caused changes in the blood of the volunteers. Hemoglobin levels decreased and over all white cell levels and cholesterol levels increased. Lymphocytes decreased.
Luminescent (light-emitting) bacteria were employed to detect energetic changes in the blood. Significant increases were found in the luminescence of these bacteria when exposed to blood serum obtained after the consumption of microwaved food."
The Swiss Dr. Hans Ulrich Hertel, and a Lausanne University professor published research in the journal Franz Weber alleging that food cooked in microwave ovens could pose a greater risk to health than food cooked by conventional means and that food cooked in microwave ovens had cancerous effects on the blood. The study was undertaken with Dr. Bernard H. Blanc of the Swiss Federal Institute of Technology and the University Institute for Biochemistry
The Swiss Association of Dealers for Electro-apparatuses for Households and Industry (FEA) requested that the President of the Court of Seftigen, Canton of Bern, to issue a "gag order" against Drs. Hertel and Blanc. In March 1993, Dr. Hertel was convicted for "interfering with commerce" and prohibited from further publishing his results.
After years of appeals, the European Court of Human Rights finally reversed the decision in a judgment delivered in Strasbourg, Austria, on August 25, 1998. The court held that there had been a violation of Hertel's rights in the 1993 decision.
The European Court of Human Rights also ruled that the "gag order" issued by the Swiss court in 1992 against Dr. Hertel, prohibiting him from declaring that microwave ovens are dangerous to human health, was contrary to the right to freedom of expression. In addition, Switzerland was ordered to pay Dr. Hertel compensation.
See also: Microwaving
History
Description
A microwave oven works by passing microwave radiation, usually at a frequency of 2450 MHz (a wavelength of 12.24 cm), through the food. Water molecules in the food absorb energy from the microwave beam in a process called dielectric heating. Each water molecule is an electric dipole, meaning that it has a positive charge at one end and a negative charge at the other, and is therefore twisted to and fro as it tries to align itself with the alternating electric field induced by the microwave beam. This molecular movement creates heat. Microwave heating is sometimes incorrectly explained as resonance of water molecules, but this occurs only at much higher frequencies, in the tens of gigahertz.Hazards and controversy
Microwaving food is fast and popular, but there are hazards.
