Cooking For The Blind 104:
Thinking About Heat
Heat is kind of a weird thing.
For the most part, on a molecular level, heat is destructive.
It smashes things apart; neatly-folded protein molecules unravel, long chains of carbohydrate molecules get bent out of shape and start absorbing water, and complex sugars get busted up into smaller, sweeter, simpler sugars.
Heat moves through things, too. It starts at your heat source, and makes its way to your food a number of ways.
In an oven, heat gently rises up from the bottom of the oven where the heating element lives. If its a convection oven, then a fan blows heated air over the food. If you turn the broiler on, then intense heat radiates downwards.
Heat may be applied directly to the outside of your food, by steam, which carries the same heat that allowed it to evaporate, or perhaps your food is heated by hot oil, whose heavier molecules don’t begin to boil at 212ºF.
Once it touches the surface of the food, the heat starts to move inwards (there’s that 2nd law of Thermo again).
Think about it: especially with larger pieces of food, like a beef roast, turkey or large root vegetables, whats the last place to get hot? The inside. Heat takes time to move through things from the outside in.
Of course, if heat has nowhere to go, it stays put. That’s what preheating a pan does, or preheating an oven.
Preheating a pan on a heat source is letting it absorb as much heat as it needs to; think of it as charging your electronic device for use, except instead of electrical energy, its thermal energy. It needs to charge fully with energy before it can start to do the work that is asked of it.
The pan is touching the air, and is certainly still giving off heat (because you can feel the heat coming off of it with your hand), but the pan has a much harder time giving its heat to the air, which isn’t very dense.
Once you put food in direct contact with that pan, there’s more mass for the heat to flow into, and so the thermal energy rushes in.
Sizzle.
Feel heat radiating out form the source, feel it moving. Controlling the type, intensity, and duration of this heat is one of your main tools of transformation.
Feel it moving through the air, feel it radiating off cooked food.
Notice that when you cut open a medium rare roast, that the outside is hot, and as you move your fingers over the surface of the inside that you have cut, it gradually gets cooler, eventually becoming the exact temperature in the center that you want it to be.
Heat is so much more than simply making cold foods hot; heat transforms. It releases volatile aromatic oils, it smashes apart sucrose molecules into a wonderful circus of flavor compounds, it melts, browns, softens and hardens.
Be mindful of what heat does,
and mindful of how heat moves.
