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Since the primary chemical reactions in cooking are triggered by heat, let’s take a look at a chart of the temperatures at which the reactions we’ve just described begin to occur, along with the temperatures that we commonly use for applying heat to food:

Temperatures of common reactions in food (top portion) and heat sources (bottom portion).

There are a few “big picture” things to notice about these common temperatures in cooking. For one, notice that browning reactions (Maillard reactions and caramelization) occur well above the boiling point of water. If you’re cooking something by boiling it in a pot of water or stewing it in liquid, it’s impossible for high-heat reactions to occur, because the temperature can’t go much above 216°F / 102°C, the boiling point of moderately salted water. If you’re cooking a stew, sear the meats and caramelize the onions separately before adding them to the stew. This way, you’ll get the rich, complex flavors generated by these browning reactions into the dish. If you were to stew just the uncooked items, you’d never get these high-heat reactions.

Another neat thing to notice in the temperature graph is the fact that proteins denature in relatively narrow temperature ranges. When we cook, we’re adding heat to the food specifically to trigger these chemical and physical reactions. It’s not so much about the temperature of the oven, grill, or whatever environment you’re cooking in, but the temperature of the item of food itself.

Which brings us to our first major aha! moment: the most important variable in cooking is the temperature of the food itself, not the temperature of the environment in which it’s being cooked. When grilling a steak, the temperature of the grill will determine how long it takes the steak to come up to temperature, but at the end of the day, what you really want to control is the final temperature of the steak, to trigger the needed chemical reactions. For that steak to be cooked to at least medium rare, you need to heat the meat such that the meat itself is at a temperature of around 135°F / 57°C.

Denaturing Proteins

What’s all this talk about “denaturing” proteins? It’s all about structure.

Denaturing refers to a change in the shape of a molecule (molecular conformation). Proteins are built of a large number of amino acids linked together and “pushed” into a certain shape upon creation. Since the function of a protein is related to its shape, changing the shape changes the protein’s ability to function, usually rendering it useless to the organism.

Think of a protein as a bit like the power cable between a laptop and an outlet: while it has a particular primary structure (the cord and wires inside it), the cord itself invariably gets all tangled up and twisted into some secondary structure. (If it’s anything like mine, it spontaneously “retangles” itself regardless of attempts to straighten it out, but proteins don’t actually do this.)

On the molecular level, the cable is the protein structure, and the tangles in the cable are secondary bonds between various atoms in the structure. Atoms can be relocated to different bonding spots, changing the overall shape of the molecule, but not actually changing the chemical composition. With its new shape, however, the molecule isn’t always able to perform its original function. It might no longer fit into places that it used to be able to go, or given the new conformation, other molecules might be able to form new bonds with the molecule and prevent it from functioning as it used to.


1. Heat Transfer and Doneness

The idea that you can just cook a steak any old way until it reaches 135°F / 57°C sounds too easy, so surely there must be a catch. There are a few.

For one, how you get the heat into a piece of food matters. A lot. Clearly the center of the steak will hit 135°F / 57°C faster when placed on a 650°F / 343°C grill than in a 375°F / 190°C oven. The hotter the environment, the faster the mass will heat up, thus the rule of thumb: “cooking = time * temperature.” Consider the internal temperatures of steak cooked two ways, grilled and oven-roasted:

Schematic diagram of temperature curves for two imaginary steaks, one placed in an oven and a second placed on a grill.

Cooking a steak on a grill takes less time than in an oven, because energy is transferred faster in the hotter environment of the grill. Note that the error tolerance of when to pull the meat off the grill is smaller than pulling the meat from the oven, because the slope of the curve is steeper. That is, if t1 is the ideal time at which to pull the steak, leaving it for t1+2 minutes will allow the temperature of the grilled steak to overshoot much more than one cooked in the oven.

This is an oversimplification, of course: the graph shows only the temperature at the center of the mass, leaving out the “slight” detail of the temperature of the rest of the meat. (It also doesn’t consider things like rate of heat transfer inside the food, water in the meat boiling off, or points where proteins in the meat undergo phase changes and absorb energy without a change in temperature.)

Another thing to realize about heat transfer is that it’s not linear. Cooking at a higher temperature is not like stepping on the pedal to get to the office faster, where going twice as fast will get you there in half the time. Sure, a hotter cooking environment like a grill will heat up the outer portions of the steak faster than a relatively cooler environment like an oven. But the hotter environment will continue to heat the outer portions of the steak before the center is done, resulting in an overcooked outer portion compared to the same size steak cooked in an oven to the same level of internal doneness.

What’s the appeal of cooking on a hot grill, then? For the right cut of meat, you can keep a larger portion of the center below the point at which proteins become tough and dry (around 170°F / 77°C) while getting the outer portion up above 310°F / 154°C, allowing for large amounts of Maillard reactions to occur. That is, the grill helps give the outside of the steak a nice brown color and all the wonderful smells that are the hallmark of grilling—aromas that are the result of Maillard reactions. The outside portion of grilled meat will also have more byproducts from the Maillard reactions, resulting in a richer flavor.

Juggling time and temperature is a balancing act between achieving some reactions in some portions of the meat and other reactions in other parts of the meat. If you’re like me, your ideal piece of red meat is cooked so that the outer crust is over 310°F / 155°C and the rest of the meat is just over 135°F / 57°C, with as little of the meat between the crust and the center as possible being above 135°F / 57°C. 

“Cooking = time * temperature”

This has to be one of the hand-waviest formulas ever. I hereby apologize. To make up for it, here’s an actual mathematical model for temperature change as a function of heat being applied. Remember to cook until medium-rare...

SOURCE: M. A. BELYAEVA (2003), “CHANGE OF MEAT PROTEINS DURING THERMAL TREATMENT,” CHEMISTRY OF NATURAL COMPOUNDS 39 (4)


1.1. Temperature gradients

This balancing act—getting the center cooked while not overcooking the outside—has to do with the rate at which heat energy is transferred to the core of a food. Since cooking applies heat to foods from the outside in, the outer portions will warm up faster, and because we want to make sure the entire food is at least above a minimum temperature, the outside will technically be overcooked by the time the center gets there. This difference in temperature from the center to outer edges of the food is referred to as a temperature gradient.


Note:

Choose the method of cooking to match the properties of the food you are cooking. Smaller items—skirt steak, fish fillets, hamburgers—work well at high heats. Larger items—roasts, whole birds, meatloaf—do better at moderate temperatures.


Lower heat sources bring up the temperature of the meat more uniformly than hotter heat sources.

All parts of our example steak are not going to to reach temperature simultaneously. Because grill environments are hotter than ovens, the temperature delta between the environment and the food is larger, so foods cooked on the grill will heat up more quickly and have a steeper temperature gradient.

1.2. Carryover

Carryover in cooking refers to the phenomenon of continued cooking once the food is removed from the source of heat. While this seems to violate a whole bunch of laws of thermodynamics, it’s actually straightforward: the outer portion of the just-cooked food is hotter than the center portion, so the outer portion will transfer some of its heat into the center. You can think of it like pouring hot fudge sauce on top of ice cream: even though there’s no external heat being added to the system, the ice cream melts because the hot fudge raises its temperature.

The amount of carryover depends upon the mass of the food and the heat gradient, but as a general rule, I find carryover for small grilled items is often about 5°F / 3°C. When grilling a steak or other “whole muscle” meat, pull it when it registers a few degrees lower at its core than your target temperature and let it rest for a few minutes for the heat to equalize.


Note:

To see how this works, try using a kitchen probe thermometer to record the temperature of a steak after removing it from the grill once it reaches 140°F / 60°C, recording data at 30-second intervals. You should see the core temperature peak at around 145°F / 63°C three minutes into the rest period for a small steak.


Simple Seared Steak

Get a cast iron pan good and hot over medium-high heat. Take a steak that’s about 1″ / 2.5 cm thick, rub lightly with olive oil, and sprinkle with salt and pepper. Drop the steak onto the cast iron pan and let it cook for two minutes. (Don’t poke it! Just let it sit and sear.) After two minutes, flip and let cook for another two minutes. Flip again, reduce heat to medium and cook for five to seven minutes, until the center is about 135°F / 57°C. Let rest on cutting board for five minutes before serving.

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