Can an induction hob heat a wok as much as a gas burner?

Question

I have often heard it said that it's essential to use a gas burner for cooking fried rice because you need to get the wok very hot, and only a gas burner has that kind of heat. (they're referring to those jet engine kind of burners)

However, I have an induction hob at home, and it has a "Power" setting, which can be used to get a pan of water boiling very quickly. The power of that setting is terrifying, but I don't know exactly how many Watts it's delivering.

I wonder if an induction hob shaped to match a wok, like this one, might actually have as much heating power as a gas burner:

My questions:

1. How much actual power (in Watts) is delivered by a wok gas burner? I.E. If I added 1 litre of water to the wok, how long would it take to raise the temperature of that water by 1 degree?
2. Does anyone know if these wok induction hobs are actually used in practice, cooking fried rice for the kinds of people who would notice if their rice wasn't fried properly?

Answer 1

TL;DR: you can make this work, but it will require adaptation, and you need to get a high-powered burner

Despite not being Asian, I cook in my woks a lot. When I shopped for a new stove, I chose to get gas, and making wok cooking easy was one of the reasons. Several wok cooking techniques rely heavily on being able to move the wok while continuing to heat it, and only gas permits that.

However, there are folks who disagree, such as Jon Kung. In a video, he demonstrates that you can definitely make fried rice in a wok over induction. You'll notice that his technique is different, though; it's all spatula, and pretty much no shaking the wok. So clearly, it can be done, although I'll note that quality wok induction burners are quite expensive.

"How fast does water boil" is pretty much the exact wrong measure for whether a burner will work for a wok. One rarely, if ever, boils water in a wok. Instead, you need to know:

• What's the maximum temperature that the burner supports? Wok-frying needs to go to at least 500F (260C), and many induction burners stop at 400F or 450F.
• How quickly does the burner return the wok to temperature after ingredients cool it?

It's the latter part that makes conventional electric elements fail for woks; no matter how hot those resistance elements get, they take a long time to get there. Induction is much more promising.

As for heat equivalents: the coventional multiplier for converting electric watts to BTU is 3.41. Thus, the induction burner that Kung recommends would be about (1500 x 3.41) the equivalent of a 5000BTU gas burner, which would be pretty low. However, as you note, a lot of heat is lost by gas burners. Induction is around 90% efficient, whereas gas is as low as 40%.

So that 1500W burner would be equivalent to ( 1500 * 3.41 * (90/40) ) a 11500 BTU gas burner. Still pretty underpowered for stir-frying, though; notice that Kung gets around this by making very small batches. For comparison, I use a 25000BTU gas burner, and restaurant ones go up to 150000. So you're going to want an induction burner that's at least 2500W, which is more easily done in Europe than in the USA, where it would require special wiring in the kitchen.

Answer 2

I had a chance recently to measure the power delivered by a reasonably high power gas burner. A professional Taiwanese chef was using it to cook egg fried rice, which everyone agreed tasted delicious, so I am going to assume it was of sufficient power.

I placed 500g of water in the wok and let the temperature equilibrate for a few seconds, then measured the temperature. Then I put the gas burner on full blast for 10 seconds, then switched it off and let the water equilibrate again for a few seconds.

The initial water temperature was 22.8ºC. After heating, the water was 44.3ºC; a rise of 21.5ºC.

The specific heat capacity of water is 4184 J/(kg K), meaning that approx 45 kJ of energy had been delivered to the water, over 10 seconds. Or 4.5kW of power over that period.

Most consumer induction hobs only seem to go as high as 3kW (presumably measured on the wire, and not as actual power delivered to the wok) so probably aren't delivering as much power as this gas burner.

However, some commercial induction hobs designed for woks, like the Target Catering Equipment range can go as high as 5kW. However, it's not clear if that's the maximum power consumed by all the rings together, or the maximum power that a single ring is capable of.

In conclusion, consumer induction hobs aren't far off the power, but don't get as high as needed, but some companies may produce hobs with enough power.