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Old 11-13-2012, 11:06 AM   #4
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I'm going to put this in here and refer back to it when it comes up in threads. It's a long read, but it should really clear a few things up and hopefully help:

Whether cooking a Ia plancha or in a frying pan, people usually cook food on one side and then, about halfway through, flip it over to finish cooking it from the other side. The assumption is that this will cook the food more evenly from edge to edge. But is it the best approach?

No! A single flip cooks the food neither fastest nor most evenly. It just takes less thought. Food flipped twice will cook with greater uniformity; flip it four times for more even cooking still; and so on. Surprisingly, the more you flip, the faster the food cooks, too. Food science writer Harold McGee discovered these flipping effects, and we have verified them (see next page).

Uneven cooking happens whenever there is a gradient between the surface temperature of the food and the temperature at its core. The bigger the difference between these temperatures, the more uneven the cooking is. When food is cooked in a pan or on a griddle at 300 c / 572 p, the layers just below the surface of the food quickly reach the boiling point of water, even as the core remains much cooler. The temperature of the food surface rises the boiling point and stays there until the food dehydrates and browns. If you cook it for too long, the dry crust eventually burns.

Typically, the cook flips the food over before that can happen. Unfortunately, by that time, much of the food beneath the surface has been overcooked. Yet the core of the food is still undercooked. That's why you have to continue cooking the other side for nearly as long again.

While the flipped food cooks on its back side, the just-cooked surface temperature starts to cool down. Three mechanisms are at work simultaneously. First, some of the built-up heat at and near the surface diffuses through conduction toward the center of the food. Second, the hot later at the surface evaporates as steam. Finally, some of the built-up surface heat slowly convects away into the relatively cooler air of the k kitchen. The total effect is to cool the cooked surface and heat the core.

Because the heat doesn't brake to an immediate stop but keeps on rolling toward the center, experienced cooks know to pull food from the
griddle just before it's perfectly done. They then allow time for the residual heat to sink in, a process called resting. But how do you know exactly when to remove the food? Predicting how much the core temperature will rise during resting is difficult. Usually, cooks build up an intuition for the timing during years of trial and error.

Fortunately, there is an alternative approach that, although more laborious, is more likely to succeed for most cooks: frequent flipping. The more often you flip the food, the less time it spends against the griddle, and the less time the heat has to build up below the surface of the food. The result is that the overcooked layer is minimized, and more of the center is done just right.

In essence, constant flipping reduces the size of the swings that the surface temperature takes as the food surface alternates between cooking and cooling. It also lowers the average temperature of the surface, which means that, edge to edge, the food ends up more evenly cooked.

This effect shouldn't be too surprising. Most of us intuitively understand that rotating a roast on a spit helps cook the roast more evenly. Flipping food back and forth creates pulses of heat that produce very much the same result-both a golden crust and an evenly cooked interior.

Repeated flipping also speeds the cooking a bit because, in much the same way that it minimizes how much excessive heat builds up on the cooking side, it also reduces the amount of cooling that occurs on the resting side. Flip too frequently, however, and you'll get diminishing returns.

How often, then, should you flip? There is no single optimum, but somewhere in the range of once every 15-30 seconds seems reasonable.

Give it a try, and you'll discover the advantage of this unorthodox approach. Because the surface and core temperatures of the food never get very far apart, the interior temperature rises just a few degrees during resting. It thus becomes easier to estimate when to stop cooking, and timing things just right becomes less critical.
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