How Induction Cooktops Make Meals with Magnets

By Andrew Tarantola on at

It's a disgrace—98 percent of US households still cook food over crude heat like a bunch of cave-dwelling heathens. Well, the 21st century is no place for such pyromantic parlor tricks. We've harnessed the power of electricity, and adapted it for the next wave of culinary hardware—induction ranges. Here's how they can drag our sorry kitchens into the modern era.

People cook food in one of four primary ways. Traditional gas and electric ranges work by maintaining an energy source (ie the individual burner or coil). This heats whatever part of the cooking vessel in contact with it, and the energy transfers in a process known as convection cooking. This, unfortunately, is energetically inefficient, and it heats just those contacted parts of the vessel, leading to uneven cooking temperatures and scorched chocolate puddings. The third method is the microwave—because it simply heats the food itself, a microwave is the most efficient way to cook food. But method number four, induction, saves energy as well, and it does so by not heating the air surrounding the pan—induction simply creates a heat source in the pan itself.

An induction cooktop heats up an electrically conductive object by sending an electromagnetic current through the object's mass. The right kind of object resists the current flowing through it. That resistance generates an effect called eddy currents, and those currents create heat. Turn on an induction burner, and it creates a strong enough magnetic field to induce these heat-making eddy currents in any object that's attracted to a magnet.

When a piece of ferrous cookware, say, a cast iron frying pan or a steel griddle is placed on the surface, about one volt of energy is transferred (induced if you will) into the item. This charge, along with it's associated magnetic field, excites the items molecules in the pan. More importantly, the current moving through the ferrous material is running into stiff resistance from the iron molecules in the pan, which causes Joule heating. By adjusting the strength of the AC electromagnetic field, we can precisely control how hot the vessel becomes and how quickly it will convectionally cook its contents.

The induction method is also affected by other environmental variables such as the object's size, material, and skin depth. Non-ferrous materials like copper, glass, ceramic, or aluminum will not heat on an induction range. Being non-magnetic, the current encounters less resistance and produces little heat. Skin depth, also known as magnetic permeability, works to concentrate the current near the surface of the metal. A thinner skin increases the amount of electrical resistance at the surface of the cooking vessel while working to reduce heat generated by the induction coil.

The induction coil itself is made of litz wire—a big wire composed of smaller insulated wires running in parallel. It's designed so that when interacting with the bottom of the vessel, the coil effectively forms a transformer, stepping down voltage while increasing current and the relative resistance of the pot. This causes most of the heat energy to concentrate in the pot, not the coil or the glass-ceramic range surface, leaving them cool to the touch as soon as the pan is removed.

This aids safety—with induction, you can't contact an open flame or melt your hand on a recently-used electric heating coil. Induction also has vastly more thermal efficiency, converting 85-90 percent of the current into heat, while comparable gas and electric ranges are rated at 40 and 70 percent, respectively. This efficiency also allows induction ranges to to heat up 20 to 50 percent faster than electric ranges, which reduces cook times, but maintaining the precise heat control of gas at a fraction of its needed energy input. Since induction ranges typically require a stronger, rapidly-alternating AC currents than are available in American homes, most ranges incorporate a raft of transformers, rectifiers, and inverters to boost the current at the induction coil to as much as 1000 times what is coming out of the wall. Technology within the appliance can often detect whether or not a cooking vessel is present, or if its contents have boiled dry.

"It's a fun way to cook, perfect for a geeky man's kitchen. I'm not a recipe cook, but this makes you more precise." chef Sean Rembold, of Brooklyn restaurant Marlow & Sons, told Popular Mechanics.

On the other hand, induction ranges do still have some bugs to work out. First of all, the price is significantly more expensive that conventional gas and electric ranges. Stovetops typically start at just under £2000 and can top out at over £4000. In addition, just because these ranges are more thermally efficient, they haven't yet proven cheaper to operate than gas or electric. What's more, if you've just laid out hard earned cash for a shiny new full set of copper cookware, you are out of luck. Here's the rule: If a magnet will stick to it, it will work on an induction cooktop.

Induction has been adopted with some success in Europe. In America, there's the basic problem of unfamiliarity, but there's also a mechanical barrier—most of the high-end kitchens that could afford an induction upgrade are already plumbed to fuel and vent a massive gas range.

Wikipedia 1, 2 - How Stuff Works 1, 2 - Popular Mechanics - The Induction Site - Induction Cooktop - GE Appliances - Image: mskorpion/Shutterstock]