TEMPERATURE


by: ROBERT. L. WOLKE

The WASHINGTON POST


Q I have a question regarding the temperature of a roast.


. Emeril Lagasse, the famous Food Network chef, says to remove the meat from the heat source before it gets to the desired temperature. He claims that as it” rests,” its temperature will continue to rise and it will keep on cooking. My physics knowledge, poor as it is,’ tells me that with no heat source, the meat must cool down, not get hotter. Is Emeril correct?


A Of course Emeril and other chefs are correct.

  Would I argue with Emeril Lagasse? He’s bigger than I am. It does seem counterintuitive that a piece of meat just resting on the counter could grow hotter. That would violate the most fundamental law of physics: You can’t get energy from nowhere. But while the meat rests, its internal temperature indeed rises from 5 to 15 degrees, depending on its size and shape. This effect is called carry-over cooking.”


The source of the heat is the outer portions of the roast, which had been exposed most directly to the oven’s hot air and are therefore hotter than the interior. The resting time allows some of the extra heat at the surface to work its way into the interior, thereby raising its temperature and, as a result, cooking it further.


A roast should always be taken out of the oven before its interior reaches the desired final temperature. That’s not only to avoid overcooking, but also to allow the juices to redistribute themselves throughout the roast.


In baking, however, a cake maker usually tests for the batter to be fully set before removing the cake from the oven. Shouldn’t this result in over-baked cakes? After all, you can’t turn off conduction. Or is there some chemistry going on that I, as a mere physicist, am unaware of? Finally, why can’t a thermometer be used to deter-mine when it is done?


A toothpick test — whereby a toothpick inserted into a cake’s center comes out dry — is the ultimate test of doneness, signaling that all the wet batter has turned into cake. But unlike the deepest parts of a rib roast or leg of lamb, all parts of the batter in a cake pan are relatively close tr) the surface, so there won’t be a big temperature difference between the surface and the interior. Any such difference. will even out in baking because wet batter is a good conductor of heat — much better than meat. Because the surface isn’t much hotter than the interior, little if any carry-over cooking will take place after the cake is out of the oven.


A thermometer is not of much use, because all cakes and pans are different. We can’t specify a desired ‘finish” temperature for cake as w can with beef, for example: 120 to 130 degrees for rare, 140 to 150 degrees for medium and 170 to 185 degrees for ruined. These are the final temperatures after resting.



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