Somehow, I’ve got involved in a discussion about how cooking methods effect how quickly food cools.
The other person involved says that food cooked slowly will stay warm longer than food cooked quickly, such as in a microwave. She can’t explain why; she’s convinced it’s true because she’s observed it.
I don’t see how this is possible. I think she probably has observed a difference, but that it’s due to variables she can’t control–she’s not working in a lab, but a food kitchen. (Even if she ladles soup from the microwave and soup from the stove into the same type of bowl in the same amount, she’s not going to be able to tell the difference between 300 degrees and 400 degrees. Plus, microwaves don’t heat uniformly, so the soup may be hotter where she’s sticking her finger.)
So, my question is: Is it true that food cooked slowly will stay warm longer than food cooked quickly, if everything else is the same? If so, why?
Heat takes time to diffuse through food. Items that are cooked quickly will be hot on the ouside, but still relatively cool in the center. Foods that are slow-cooked reach a more homogenous temperature throughout. The foods that are much cooler in the center than they are on the outside will seem to cool off more quickly than a similar food item that has been allowed to cook slowly and reach a higher core temperature.
If everything else is the same, no. The molecules have no way of remembering how long they took to reach their current temperature. Cooling will thus depend only on present and future conditions, not on the past.
But if the rapid heating had the effect of raising the surface temperature while leaving other areas cooler, then this would affect the rate - since it would mean that the total heat energy was lower.
No, it’s not true.
The rate of transfer of heat to the environment is completely independent of how an object is heated. Two identical foods, heated to the same temperature, will cool at the same rate.
What is true is that when you heat something slowly, and for a long time, you will get the entire thing to a uniform temperature, and when you heat something quickly, the outside of the object will get piping hot long before the innards reach a high temperature. That means that while a slow cooked and a flash heated steak may have the same surface temperature, the slow cooked meat will have a higher over all temperature (more heat content), and will take longer to cool than a steak that’s burnt on the outside and frozen in the middle.