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The Science of Cooktops

Here’s what you need to know about how they work.

by David Joachim, Andrew Schloss

fromFine Cooking
Issue 120

Skill plays an important role in cooking, but it’s not the only thing that makes a great cook. The ingredients you choose, the recipes you follow, and the pots and pans you use also have an impact on your cooking, and those can always vary. But what about the one constant in your kitchen, your cooktop? Let’s take a look at three of the most common cooktop technologies—gas, electric, and induction—to see how they operate, and the pros and cons of each.

Go under the hood: View our infographics to see up close how dual-fuel ranges, convection ovens, and induction cooktops work.

How do gas cooktops work?

A gas stove burner consists of a burner assembly attached to a small gas valve that is connected to the main gas line. When you turn the knob, the intake valve opens and gas flows through a venturi tube, a wide pipe that narrows in the middle. Gas enters through one of the wide ends, and as it passes into the narrowed section, its pressure increases. There is a small air hole in the section where the pipe widens again, and as the gas moves into this section, the pressure releases, sucking oxygen into the air hole. The oxygen mixes with the gas, making it combustible. The oxygen-gas mixture then flows into the burner.

The burner is simply a hollow metal disk with holes punctured through its perimeter. A gas pilot light or electric pilot sits to one side of the burner and sends a small flame or spark to ignite the oxygen-gas mixture as it flows through the holes in the burner. By turning the knob to a higher heat setting, you increase the flow of gas and air, and the flame gets larger.

Gas burners can work with either natural gas or propane. Both are hydrocarbon fuels, and their hydrogen content makes the gas flame appear blue. A yellow or orange flame indicates an excess of oxygen and a slightly cooler temperature. The orange color comes from unburned carbon. It’s natural for the tips of the flames on a gas burner to appear yellow-orange where the flame is cooler, but if the entire flame appears yellow, the ratio of gas to oxygen is too low, and the gas burner or intake valve may be clogged and need cleaning. A red flame is cooler still and typically causes soot (unburned carbon) to appear on the bottoms of pans.

Pros Gas burners can change temperature instantly, moving from high to low heat with the turn of a knob. Gas is also the only stovetop technology that provides an easily controllable open flame for roasting peppers, browning tortillas, or stir-frying in a traditional rounded-bottom wok.

Cons Gas is the least e‚ffcient fuel source at heat transference; up to 60 percent of the heat generated by a gas burner can escape into the air instead of going in the pan. Also, not all utility companies supply natural gas, although you can have propane regularly delivered to a tank on your property. By volume, propane contains about 2-1/2 times the usable energy of natural gas, so less propane is needed to produce the same amount of heat as natural gas. But since propane flows at a different pressure, you can’t use it with a cooktop made for natural gas, unless you convert the cooktop for propane use. Converting the cooktop will reduce its BTU output (the unit that measures gas energy content), and a poor conversion or installation can also lower BTUs.

How do electric cooktops work?

Electric burners are typically coil style: a flattened spiral of electrical wire sheathed in metal that heats up when the control knob is turned on, triggering electricity to flow into the wire. You can see the intensity of the electrical flow in the glow of the burner. (European-style electric burners are built similarly except the wire is embedded in a solid metal disk.) In a smoothtop electric cooktop, the coils are placed under a single sheet of heat-tempered glass-ceramic material that covers the cooktop. The electric coils heat in the same way, radiating heat into the glass, which radiates it into pots and pans. Halogen electric cooktops are similar, except the heating elements are rings of halogen bulbs under the glass rather than electric coils.

Pros Electric burners are flat, so the heat from the burner—whether coil-style or smooth top—comes in contact with the bottom of the pan. Therefore, it conducts most of its energy (about 75 percent) directly into the pan, rather than radiating it into the air as a gas flame would. Smooth tops and sealed European-style burners also have the advantage of being easy to clean. Another plus for smooth glass-ceramic cooktops: They don’t get nearly as hot as the pots and pans, so there’s less danger of burning yourself on the stovetop, and spills are less likely to burn on the cooktop’s surface.

Cons Poor heat control is the biggest knock against electric cooktops; the heating elements simply respond more slowly than those on gas or induction cooktops (more on those in a minute). To overcome this deficiency, you can set two burners at different temperatures if you know you’re going to need instantaneous control. For example, bring rice to a boil over high heat on one burner, and when you want to immediately reduce the heat to a simmer, simply move the pan to the second burner on lower heat.

There are also a couple of other drawbacks specific to smooth-tops. The glass-ceramic surface is a poor heat conductor, so it transfers heat to pans more slowly than metal-top electric stoves. Also, glass-ceramic cooktops scratch easily, so if you’re in the habit of sliding and shaking pans on your burners, you’ll have to change your ways when working on a smooth-top range if you want to keep it looking good.

How do induction cooktops work?

With induction technology, heat is generated in the pan itself, not in the heating element. Induction cooktops are powered by electricity, but the “element” that rests beneath the ceramic or glass surface functions like a powerful magnet, which generates a magnetic field. When you put a large piece of magnetic metal, such as a cast-iron skillet, into that field, the electrons in the pan try to align with the magnet in the cooktop. But the cooktop magnet alternates its poles, causing the pan’s electrons to move at such a rapid rate that the electrical current induces the pan to generate heat, which it does very quickly. You control the amount of heat produced in the pan with a knob on the cooktop that increases or reduces the strength of the magnetic field.

Pros Induction cooktops offer instantaneous and precise heat control, even at very low temperatures. And unlike gas, induction is extremely heat e“fficient. Since the heat is generated in the pan itself, most of it (about 85 percent) stays in the pan, cooking food slightly faster than gas burners and much faster than electric burners. If you’re new to induction, you may find that pots boil over sooner, so watch closely. Relatively little heat is lost in the air, which means that induction cooktops won’t heat up your kitchen as gas or electric cooktops can—an advantage in the summertime or in a crowded kitchen. Plus, the cooktop itself stays cool, a nice safety bonus. If you put a magnetic pan over half of an induction element, the other half of the element stays cool to the touch.

Cons And that brings us to the biggest disadvantage of induction: You have to use cookware that’s high in iron. That includes cast iron—whether enameled or not—and high-iron stainless steel. Pure copper, aluminum, glass, earthenware, stoneware, and some low-iron stainless steel cookware won’t work. (To test your cookware, hold a magnet to the bottom. If the magnet sticks, the cookware will work on an induction cooktop.) Also, the pan must make direct contact with the cooktop on an induction unit, so flat-bottom sauté pans and woks work well, but not rounded-bottom woks or old, warped cookware.

Another potential drawback to an induction cooktop is that you can’t use it to roast a pepper or toast tortillas. Also, the cooktop may become scratched from vigorous pan shaking. And some lower-quality cookware with loose-fitting handles, lightweight lids, uneven bottoms, or poorly clad layers of metal can vibrate so much in the high-frequency oscillation of the cooktop’s magnetic field that they actually generate noise.

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