Induction cooking: Difference between revisions

An induction cooker uses induction heating for cooking. Usually a ferromagnetic or ferromagnetic coated pot is placed above an induction coil for the heating process to take place. This type of hob (stove top) does not work with non-ferromagnetic cookware, such as glass, aluminum, and most stainless steel.

Induction cookers are faster and more energy-efficient than traditional stoves. Additionally, the risk of accidental burning is diminished since the hob itself only gets marginally hot (due to heat conduction down from cookware), allowing direct contact without harm. Also, no heat is lost to the air directly from the hob, keeping the kitchen containing the cooker cooler.

Since heat is being generated from an electric current induced by an electro-magnet, the range can detect when cookware is removed or its contents boil out by monitoring the resistance to the current. In theory, this creates 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, plus the same or greater degree of controllability as gas. Water in a pot begins to boil (at its contact points with the pot) in as few as 5 seconds, and then upon turning down immediately (in a second) transitions to simmering.^{[citation needed]}

The amount of time that it takes a pot to boil is proportional to the power or wattage that the induction hob is using. Low wattage induction coils can take as long to heat as the similar wattage in an ordinary electric burner. Thus, the time can be from 3 minutes to around 10 minutes for 3600 watts to 1200 watts induction hobs.

It is considered safer because there are no open flames and the element itself is not hot to the human touch; only the pan becomes hot. Bosch brochures, for example, show a person touching the ceramic cover to the inductor while along side is a pan of boiling water heated by the same induction source.

It is also easier to clean because it is one large flat, smooth surface, even though it may have 2, 3, 4 or even up to 8 zones of heating induction. In addition, it doesn't suffer from the problem ceramic hobs have when pans boil over: because the surface of the hob itself doesn't get hot the food cannot get "burnt on".

Induction cookers are considerably more expensive than traditional cookers, but consume half as much electricity as electric cookers 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]} When comparing the running costs of induction cooking and gas cooking, one also needs to consider the relative prices per kWh of electricity and gas. It may be the case that gas is considerably cheaper, making cooking with gas cheaper than induction cooking, despite the fact that gas cookers are less efficient in heat transfer.

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 which is easily cleaned. The pot is placed on the glass coating, and begins to heat up along with its contents.

In induction cooking, Heat is generated in two ways:

1. Magnetic hysteresis. The rapidly oscillating magnetic field causes power in the magnetic field to be converted to heat in the ferromagnetic base of the pot due to hysteresis. The amount of heat produced is proportional to the area of the hysteresis loop. This is the primary source of heat.
2. Eddy currents. The magnetic field produces electric currents (known as eddy currents) in the metal base of the pot, and these cause resistive heating of the metal.

The heat from the pot is then transferred to the food by conduction, but very little heat is transferred to the actual stovetop. After boiling a pot of water, the surface of an induction stove is slightly warm to touch but not so warm as to burn or even hurt human flesh. Furthermore, within 1 to 5 seconds it cools to room temperature.

However, a pot or saucepan with a copper base or made of aluminium will not work on an induction cooktop. As an induction cooktop relies on the two methods itemised above to generate heat, copper and aluminium, which are not ferromagnetic materials, will perform poorly. Note that eddy currents will be generated in the copper and aluminium, but commercially available induction cooking cannot generate sufficient heat via eddy currents alone in copper and aluminium saucepans for effective heating. Pyrex glass and ceramic containers will not be heated by either method, as such containers are neither ferromagnetic, nor capable of carrying eddy currents.

Market for induction hobs is dominated by German players, such as AEG, Bosch and Siemens. The Italian firm Smeg is also a key player in this market. Prices range from about £400 to £1000.

For those starting out, there are stand-alone induction hobs that are relatively inexpensive, around $100 USD, give or take $30. These units run on even 110 volts, which is less than the typical 220 volts in Europe. The units have timers and variable heat settings, from lows of 120 to 150 Fahrenheit to highs of 420 to 464 Fahrenheit. The ability to adjust time and temperature allows for precision cooking that is difficult to achieve with gas or even with electric. Electric burners do not cool down quickly whereas the induction coil achieves its different temperatures instantaneously or extremely quickly.

Units may have two, three, four or five induction zones, but four is the most common. Some have touch sensitive controls. Some Bosch induction stoves have a memory setting, one per hob, that is able to time the amount of heat required. For example, given an exact measurement of water and food, the memory setting can deliver just the right burst of power to bring the saucepan to the boil and then automatically turn it down to simmer for the prescribed number of minutes. Potatoes, for example, take 12 minutes to cook, whereas sweetcorn is best after just 3 minutes in boiling water. The Bosch memory can include five settings per hob - so for example the corn is automatically brought to the boil, simmered, and then turned off.

• Induction heating

• The Induction Site - Induction-cooking principles and complete equipment database
• US Department of Energy- Technical Support Document for Residential Cooking Products
• PATH Technology Inventory: Induction Cooktops