On the importance of pre-heating the wok

[Peripatetic Phil]

Shopping in Waitrose at the weekend, I picked up two remaindered packs of rice noodles :  one plain, one Singapore-style.  Both contained the same cooking instructions, which involved pre-heating the wok (dry) for two minutes before adding any oil, then adding the noodles and continuing to cook for a further three minutes.  I tried the Singapore rice noodles first, but after 30 seconds at full power on my induction cooker my wok was smoking like crazy and I bailed out -- in went the oil, shortly followed by the noodles, which then proceeded to stick to every surface in sight.  They were edible, but not right.

Today I cooked the plain rice noodles, but this time I tied my hands behind my back, turned the wok onto full power for the full two minutes, added the oil, then the noodles, and -- lo and behold -- not a single noodle stuck.

So, the moral is -- if you are intending to fry noodles, it is /essential/ to pre-heat the wok; failure to do so will either cause the noodles to stick or will require excessive oil to prevent stiction.  I have learned my lesson !

** Phil.

[fried]

Noone's yet managed to answer my question of why you can't add the oil to the wok cold and then heat it to the required temperature. I've been told chefs 'do it like that' but I can't see the science behind it.

I only stopped pre-heating my pan or wok because it's not recommended for induction.

[Peripatetic Phil]

If it takes two minutes to get to the correct temperature dry, then it will take two + delta two minutes to achieve the same temperature with oil in it, IF it can in fact reach that same temperature without the oil catching fire.  But who would want to heat oil for two minutes ?  What benefit can thereby accrue ?  Is it not better to "do what the chefs do", heat the wok dry, and then add the oil just before frying ?

** Phil.

[fried]

In other words, you don't know

[Peripatetic Phil]

In other words, you don't know

I have already stated what I know :

1) If it takes two minutes to get to the correct temperature dry, then it will take two + delta two minutes to achieve the same temperature with oil in it

2) It is by no means certain that a pan containing oil can reach the same temperature as a dry pan

3) There are no obvious benefits to heating oil for two minutes rather than heating a dry pan for two minutes and then adding the oil at the last second.

Those three are sufficient to convince me that chefs have at least three very good reasons for doing what they do.

** Phil.

[Garp]

I have no idea why it works better heating the dry wok.

But can we look at it from a scientific point of view? I assume (perhaps wrongly) that the temperature of the oil is critical to produce perfect noodles. If that is the case, how hot will the oil get, after being put in a smoking hot pan before adding the noodles, compared to how hot will the oil get after heating it from cold, in the pan to the same temperature before adding the noodles?

Could there be a difference with the noodles, Phil? Maybe try the two methods using the same noodles?

[fried]

1. I don't understand the 'delta + 2 mins' bit. Are we heating the oil or the wok?

2. I find it hard to believe that a wok won't reach the same temperature with a tbsp of oil in it, if it's added before or after the pan is hot. Again are we interested in heating the oil or the wok?

3. There are no advantages, but I can see no obvious disadvantages, oil does not catch fire or explode if it's heated for 2 minutes in a cold pan, it catches fire because it reaches a specific temperature.

I have a couple of professional chefs as friends and they haven't been able to convince me either. I think for a lot of people and chefs it's become a handed-down habit.

As I say I never though about it until I started cooking on induction, and I've never really notced any difference.

I'd love to be proved wrong, but 'chef's do it like that' doesn't wash.

[Sverige]

Cracking

[Geezah]

If you have a properly seasoned wok you need to heat the wok up to smoking temperature so the pores of the steel open and release the trapped oil making the surface non stick.
That said, most cheap woks have hot spots where the spun metal is slightly thinner and your likely to get a burn or food sticking to that particular spot.

When I fry noodles as in a chow mein, I get the wok smoking, add oil, get that smoking add noodles then toss to coat with oil, then continue cooking as normal.

My Wok.

[Peripatetic Phil]

But can we look at it from a scientific point of view? I assume (perhaps wrongly) that the temperature of the oil is critical to produce perfect noodles. If that is the case, how hot will the oil get, after being put in a smoking hot pan before adding the noodles, compared to how hot will the oil get after heating it from cold, in the pan to the same temperature before adding the noodles?

Because it is a very small quantity of oil, measuring the temperature that it has achieved after each method would not be easy -- my oil-temperature thermometer needs to be immersed in hot oil for quite some time before the displayed temperature stabilises.  But /because/ it is a very small quantity of oil (compared to the mass of the wok) I would suggest that the temperature is much the same in both cases.

Could there be a difference with the noodles, Phil? Maybe try the two methods using the same noodles?

My noodles have always stuck in the past, which I now know is because I did not pre-heat the wok.  I'm certainly not planning to conduct a controlled experiment, but I /will/ undertake to report back if any noodles stick in the future.

1. I don't understand the 'delta + 2 mins' bit. Are we heating the oil or the wok?

It was not "delta + 2 mins"; it was "2 plus delta 2 mins".  If it take 2 minutes to heat a wok weighing (say) 1Kg to the optimal temperature, it will take 2 plus delta 2 (i.e., a tiny bit longer) to heat a wok weight 1kg plus some oil weighing 15 grammes to the same temperature. We are heating the wok; the wok heats the oil.

2. I find it hard to believe that a wok won't reach the same temperature with a tbsp of oil in it, if it's added before or after the pan is hot. Again are we interested in heating the oil or the wok?

Ah, now that is a very different question.  "Are we interested in" is the key here.  I think we are interested in heating the pan; it is very easy to heat 15 grammes of oil to the optimal temperature (it would take nothing like two minutes) but quite difficult to get the pan to the correct temperature because of its thermal inertia.

3. There are no advantages, but I can see no obvious disadvantages, oil does not catch fire or explode if it's heated for 2 minutes in a cold pan, it catches fire because it reaches a specific temperature.

I have a couple of professional chefs as friends and they haven't been able to convince me either. I think for a lot of people and chefs it's become a handed-down habit.

I can see disadvantages.  Not only is there a risk that the oil may catch fire (we are talking about heating for two minutes at full power, not at 20%), but there is also a risk that the oil may denature by being heated excessively for a prolonged period, thereby changing its flavour (which is why one is recommended to really heat "non-potable" mustard oil, so as to deliberately change its flavour.

I'd love to be proved wrong, but 'chef's do it like that' doesn't wash.

You can easily try to prove yourself wrong; just try both methods and report back !

** Phil.