Induction cooking: Difference between revisions

An induction cooker uses induction heating for cooking. This heat is the result of magnetic field hysteresis loss. A conducting pot is placed above an induction coil for the heating process to take place. This type of cooktop does not work with cooking vessels that are constructed from non-conductive materials. Unlike alternatives such as electric hotplates and open-grills, an induction cooker creates no heat; only the vessel used for cooking is heated.

Induction cookers are faster and more energy-efficient than traditional cooktops. Additionally, unlike traditional cooktops, the pot is heated directly to the desired temperature rather than heating the stovetop, making the stovetop much safer from the possibility of injury. However, skin can still be burned if it comes into contact with the pot, or by the stovetop after a pot is immediately taken off. Unlike a traditional cooktop, however, the maximum temperature in the system is that of the pot, which is much less capable of causing serious injury than the high temperatures attained by flames and red-hot electric heating elements. Also, the induction cooker does not warm the air around it as other cookers do, resulting in added energy efficiency.

Since heat is being generated from an electric current induced by an electric coil, the range can detect when cookware is removed or its contents boil out by monitoring the voltage drop caused by resistance to the current. This creates possible additional functions, such as keeping a pot at minimal boil or automatically turning off when the cookware is removed.

This form of flameless cooking has an edge over conventional gas flame and electric cookers as it provides rapid heating, vastly improved thermal efficiency, greater heat consistency, plus the same or greater degree of controllability as gas.^{[citation needed]} In situations in which a hotplate would typically be dangerous or illegal, an induction plate is ideal as it creates no heat itself.

The amount of time that it takes a pot to boil depends on the power of the induction cooktop. Thus, the time can be from three minutes for 3600 watt induction stove tops, to around ten minutes for 1200 watt ones. However, boiling water is a process also largely dependent on the amount of water; the speed benefits of induction cooking are most often seen when stir-frying: a thin pan with 3 tablespoons of oil may heat up to stir-frying temperature in as little as 10 seconds.

Induction cookers are safer to use than conventional stoves because there are no open flames and the "element" itself reaches only the temperature of the cooking vessel; only the pan becomes hot. However, it must be remembered that pan could be as hot as 100 °C (212 °F) and in deep fat frying could be as hot as 200 °C (392 °F). Induction cookers are also easier to clean because the cooking surface is flat and smooth, even though it may have several zones of heating induction. In addition, food cannot burn onto the cooking surface as it is not hot.

Induction cookers have all of the drawbacks of a ceramic hobs, when compared to gas cookers, and more. They do not work with non-conductive materials, such as glass or ceramic.

Cooking with thin-bottomed pans may cause food to burn, because the temperature is often controlled by switching on and off the magnetic field, rather than changing its intensity. The pan heats up and cools rapidly, causing temperature extremes.

An induction cooker also only works well with a flat-bottomed pan. Curved pans, such as woks (despite companies selling 'induction compatible' ones), only heat on or near their point of contact with the stove, making a very small heated area. This problem also exists for electric-resistance cookers - but is worse with induction hobs; as the area of the pan placed over the coil heats instantaneously leaving the rest of the pan cold (unlike incandescent hobs which allow the cooking surface to gradually heat - distributing the heat more evenly though the pan).

Pans placed on an induction hob must contain oil or a liquid to absorb the heat otherwise the rapid increase in temperature will damage the cookware.

Induction cookers are considerably more expensive than traditional cookers, but consume half as much electricity as electric-resistance elements and are more efficient in heat transfer, achieving an absolute efficiency of 84% in US Dept of energy tests (compared to a typical 40% for a gas cooker).^{[citation needed]} According to CEG Electric Glass Company, "[Induction cooking] power savings of 40-70% are realistically achievable in comparison to conventional cooktops." CEG Electric Glass Company also states induction cooking has an efficiency rate of 90%, while Electric and Gas have efficiency rates of less than 50%.^{[citation needed]}

There are cheaper single-induction-zone cooktops available largely from Asian suppliers. This is due to Asia's more densely populated cities, therefore making this type of induction cooker popular where living space is at a premium. ^{[citation needed]} Single-zone induction cookers are available only in few in retail outlets in North America, but are widely available through online stores and auction sites; some induction hobs sell for as low as $60 USD in supermarkets. ^{[citation needed]}

Most induction cooking is done on stovetop units, which may be built into a countertop or may be a portable unit. In this style of cooking, the electromagnet is usually sealed beneath a heat-resisting glass-ceramic sheet that is easily cleaned. The pot is placed on the glass coating, and begins to heat up along with its contents. In Japan, a large percentage of rice cookers are powered by induction heating.

Induction stoves work with high frequency magnetic fields, rather than resistance. A coil made of Copper Tubing is mounted underneath the cooking surface. Alternating Current in this coil produces the varying magnetic field, that is responsible for Hysteresis loss heating of the pot material.

Pots made from electrical insulators or aluminum will as a rule not heat up on inductive cookers. Only cookware of ferromagnetic materials with the correct skin depth can sufficiently absorb the Magnetic Field and produce Hysteresis Loss. These are above all ferrites, iron, including cast iron and stainless steel, and can sometimes be checked for induction-compatibility using a magnet. Stainless steel does not respond to magnets.

Contrary to popular belief, the principle of electric heating via eddy current loss does not require magnetic materials, as any conductor is capable of heat generation via eddy current heating. Theoretically it is possible to make an induction stove that works with aluminum pots via Eddy current loss. In practice however it is easier to build one that uses magnetic hysteresis loss, and this is therefore the most common type of induction cookware.

The concept of using high frequency magnetic fields to cook with is an old one; first patents date from the early 20th century^{[citation needed]}.

Modern implementation in the USA dates from the early 1970s, with work done at the Research & Development Center of Westinghouse Electric Corporation at Churchill Borough, near Pittsburgh, PA, USA. ^{[citation needed]}

This work was first put on public display at the 1971 National Association of Home Builders convention in Houston, TX, as part of the Westinghouse Consumer Products Division display. ^{[citation needed]} The stand-alone single burner range was named the Cool Top Induction Range. It used transistors developed for automotive electronic ignition systems to drive the 25 kHz current.

Westinghouse decided to make a few hundred production units further to develop the market. These were named Cool Top 2 (CT2) Induction ranges. The development work was done at the same R&D location by a team led by Bill Moreland and Terry Malarkey. The ranges were priced at $1500 each. This price included a set of high quality cookware made of Quadraply, a stainless steel/carbon steel/aluminum/stainless steel laminate (outside to inside).

Production took place in 1973 through 1975, and stopped coincidentally with Westinghouse Consumer Products Division being sold to White Consolidated Industries Inc.

CT2 had four burners of sufficient power, about 1600 Watts. The range top was a ceramic sheet surrounded by a stainless steel bezel upon which four magnetic sliders adjusted four corresponding potentiometers set below. This design, using no through-holes, made the range proof against spills. The electronic section was made in four identical modules. Provision was made for fan cooling of the electronics.

In each of the electronics modules the 240V 60Hz domestic line power was converted to 20V to 200V continuously variable DC by a phase-controlled rectifier. This DC power was in turn converted to 27 kHz AC by two arrays of six paralleled Motorola automotive ignition transistors in a half-bridge configuration driving a series-resonant LC oscillator of which the inductor component was the induction heating coil and its load, the cooking pan.

Control electronics included functions such as protection against over-heated cook-pans and overloads. Provision was made to reduce radiated electrical & magnetic fields. There was magnetic pan detection also.

CT2 was UL Listed and received FCC approval, both firsts. Numerous patents were also issued.

Raymond Baxter demonstrated the CT2 on his BBC series, Tomorrow’s World. He showed how the CT2 could cook through a slab of ice.

Market for induction stoves is dominated by German players, such as AEG, Bosch, Miele, Schott AG and Siemens. The Italian firm Smeg and Sweden's Electrolux are also key players in the European market. Prices range from about GBP250 to 1000 within the UK. In 2006, Stoves launched the UK's first domestic induction hob on a range cooker at a slightly lower cost than those imported.

Taiwanese and Japanese electronics companies are the dominant players in induction cooking for East Asia. After aggressive promotions by utilities in HK like CLP Power HK Ltd, may local brands like icMagIC, Zanussi, iLighting, also emerged. Some of these companies have also started marketing in the West; such as Tatung, Sunpentown, Panasonic and Hitachi. However, their products available in Western markets are a small fraction of what is available in their home markets. Interestingly, some Japanese electronics giants only sell domestically. Some of the brands on the retail market in the Western US are Wolf, Viking, Thermador, GE Profile, KitchenAid, and Jenn-Air (Whirlpool Corp), all with 30" and 36" kitchen counter-top models.

Small stand-alone induction cookers are relatively inexpensive, around US$60.

Units may have two, three, four, or five induction zones, but four is the most common. Some have touch-sensitive controls. Some induction stoves have a memory setting, one per hob, to time the amount of heat required.

• Glass-ceramic
• Microwave oven
• Electrodeless lamp

• Technical Support Document for Residential Cooking Products
• Cooking Inductively: ADI iCoupler Technology Isolates the Hob and the User Interface