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Thermal inertia or "out of the fire"

When you're cooking, you need a lot of heat to cook, and most of the time it's on the fire, literally if you're on gas, more indirectly if you're not.

An expression that comes up quite often is "Off the heat", but what does it really mean?

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Keywords for this post:Cooking Heat Inertia Thermal Pan Fire

Last modified on: December 12^th 2020

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When it comes to saucepans (in the broadest sense of the word: saucepans, sauté pans, frying pans, etc.), you'll find the full range of quality, and therefore price, in the shops.
From the cheap, cheap stuff that's often lightweight, but won't last very long, to the rather chic, heavy, stainless steel pans that will last you a lifetime or more (yes, it's a bit weird to say and consider, but your pots and pans might just outlive you).

sur le feu 1

The quality saucepans I was talking about have a very thick bottom, around 1 cm of solid steel, which is welded to the pan itself.
The role of this bottom is thermal inertia, i.e. when you put it on the fire, the bottom "loads" with heat first, and separates the flame from the food being heated/cooked, which means that the contents of the pan take longer to heat up, but in the other direction, same inertia, it cools down less quickly.

sur le feu 2

So there's a "certain time" between the moment you turn off the heat, and the moment your preparation stops heating or cooking.
As a general rule, this is very practical: no sudden bursts of heat, less risk of burning, less sensitivity to false settings. It's not for nothing that all chefs' kitchens are equipped with these pans.
Note that this applies to both gas and induction, although induction is much smoother anyway (it seems to me).

Right, and?

Well, from all this, it's clear that you need to be very careful, especially if you're cooking a delicate food like fish, with the thermal inertia of your pans.
It's quite easy to overcook a food, without necessarily burning everything, because even though you've turned off the heat, it's still cooking a little.

That's why you'll find the expression "hors du feu" (off the heat) in many recipes, for example "hors du feu, ajoutez les œufs battus" (off the heat, add the beaten eggs), and it's to be applied strictly: remove your pan from the heat before continuing, otherwise, due to the thermal inertia of your pan + the residual heat of the stove (even if it's less with induction), you'll overcook and perhaps miss your recipe, which would be a great pity...

hors du feu

In practice, if you cook at the green arrow, "off the heat" is at the red arrow.

In short: When you come across the expression "off the heat" in a recipe, it's not just a matter of turning off the heat, it's also a matter of moving your pan away from the heat so as to stop cooking relatively quickly.

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