What Is "Induction Cooking"?

Induction Cooking:
How It Works

What Is "Induction Cooking"?

Here's the Basic Idea

"Cooking" is the application of heat to food. Indoor cooking is almost entirely done either in an oven or on a cooktop of some sort, though occasionally a grill or griddle is used.

Cooktops--which may be part of a range/oven combination or independent built-in units (and which are known outside the U.S.A. as "hobs")--are commonly considered to be broadly divided into gas and electric types, but that is an unfortunate oversimplification.

In reality, there are several very different methods of "electric" heating, which have little in common save that their energy input is electricity. Such methods include, among others, coil elements (the most common and familiar kind of "electric" cooker), halogen heaters, and induction. Further complicating the issue is the sad habit of referring to several very different kinds of electric cookers collectively as "smoothtops," even though there can be wildly different heat sources under those smooth, glassy tops.

As we said, cooking is the application of heat to food. Food being prepared in the home is very rarely if ever cooked on a rangetop except in or on a cooking vessel of some sort--pot, pan, whatever. Thus, the job of the cooker is not to heat the food but to heat the cooking vessel--which in turn heats and cooks the food. That not only allows the convenient holding of the food--which may be a liquid--it also allows, when we want it, a more gradual or more uniform application of heat to the food by proper design of the cooking vessel.

Cooking has therefore always consisted in generating substantial heat in a way and place that makes it easy to transfer most of that heat to a conveniently placed cooking vessel. Starting from the open fire, mankind has evolved many ways to generate such heat. The two basic methods in modern times have been the chemical and the electrical: one either burns some combustible substance--such as wood, coal, or gas--or one runs an electrical current through a resistance element (that, for instance, is how toasters work), whether in a "coil" or, more recently, inside a halogen-filled bulb.

How Induction Cooking Works:

1. The element's electronics power a coil (the red lines) that produces a high-frequency electromagnetic field (represented by the orange lines).
2. That field penetrates the metal of the ferrous (magnetic-material) cooking vessel and sets up a circulating electric current, which generates heat. (But see the note below.)
3. The heat generated in the cooking vessel is transferred to the vessel's contents.
4. Nothing outside the vessel is affected by the field--as soon as the vessel is removed from the element, or the element turned off, heat generation stops.
   
   There is thus one point about induction: with current technology, induction cookers require thatall your countertop cooking vessels be of a "ferrous" metal (one, such as iron, that will readily sustain a magnetic field). Materials like aluminum, copper, and pyrex are not usable on an induction cooker. But all that means is that you need iron or steel pots and pans. And that is no drawback in absolute terms, for it includes the best kinds of cookware in the world--every top line is full of cookware of all sizes and shapes suitable for use on induction cookers (and virtually all of the lines will boast of it, because induction is so popular with discerning cooks). Nor do you have to go to top-of-the-line names like All-Clad or Le Creuset, for many very reasonably priced cookware lines are also perfectly suited for induction cooking. But if you are considering induction and have a lot invested, literally or emotionally, in non-ferrous cookware, you do need to know the fact
   
   
   

   So How Much Power Is What?

   
   
   
   Perhaps the most useful way to use that conversion datum is to see what good gas-cooker BTU values are and work back to what induction-cooker kW values would have to be to correspond. But what are good gas-cooker BTU values? Here too, opinions will vary. As a sort of baseline, we can look at what typical mid-line gas ranges look like. As numerous sources report, a typical "ordinary" home gas range will usually have its burners in these power ranges, give or take only a little: a small burner of about 5,000 Btu/hour; two medium-level burners of about 9,000 Btu/hour; and (depending on width, 30 inches or 36 inches) either one or two large burners of anywhere from 12,000 to 16,000 BTU/hour
   
   
   as four 15,000-BTU/hour burners and two 18,000-BTU/hour burners). One expert source remarked of such gear: Most commercial-style home ranges offer 15,000 BTUs per burner, which is perfectly adequate for most at-home cooks. You won't always need all that heat, but if you want to caramelize a bell pepper in seconds, or blacken a redfish like a pro, well, you'll need all the heat you can get. My advice: Go for the big-time BTUs (which, in the tests he was discussing, was that 18,000 BTU/hour level).
   So let's summarize by showing representative gas-power levels and their induction-power equivalents (remember, calculated quite conservatively):
   

   • Typical home stove:
     
     • small: 5,000 BTU/hour gas = 0.70 kW induction
     • medium: 9,000 BTU/hour gas = 1.25 kW induction
     • large: 12,000 BTU/hour gas = 1.70 kW induction; or 15,000 BTU/hour gas = 2.10 kW induction
       
   • Typical "pro style" stove:
     
     • medium: 15,000 BTU/hour gas = 2.10 kW induction
     • large: 18,000 BTU/hour gas = 2.50 kW induction

   (Even for wok cooking, the most power-hungry kind there is, experts consider 10,000 BTU/hour good and 12,000 BTU/hour "hot".)
   So how do actual real-world, on-the-market induction cooktops stack up against gas?
   It's an almost comic mismatch. Sticking to build-in units (as opposed to little free-standing countertop convenience units), it is difficult, perhaps by now impossible, to find a unit with any element having less than 1.2 kW power--which puts the smallest induction element to be found equal to the average "medium" burner on a gas stove. The least-expensive 30-inch (four-element) induction cooktop has:
   

   • a 1.3-kW small element (between 9,000 and 9,500 BTU/hour),
   • two elements of 1.85 kW each (well over 13,000 BTU/hour), and
   • one element of 2.4 kW (over 17,000 BTU/hour).

   The least-expensive 36-inch (five-element) induction cooktop has:
   

   • a 1.2-kW small element (8,500 BTU/hour),
   • a medium element of 1.8 kW (13,000 BTU/hour),
   • a larger element of 2.2 kW (16,000 BTU/hour),
   • and two elements of 2.4 kW (over 17,000 BTU/hour).

   The very highest-power gas burner to be found in the residential market is 22,000 BTU/hour, and that's a sort of freak monster, whereas a 3.6-kW and 3.7-kW element--which is around 26,000 BTU/hour of gas!--is found in many induction cooktops. (Moreover, the elements on some induction units can share power with one another, so that if not every element is already in use, a given one can be "boosted" beyond its normal power level, for uses such as bringing a large pot of water to a boil, or pre-heating a fry skillet.)
   So, in sum, induction is not "as powerful as gas"--it's miles ahead.