[falcolas]

You're not wrong - once the food is at the right temperature, it's done. You can hold food at the "right" temperature for a long time, but if you go above it, it'll over-cook.

There's a few ways to heat food up, the most common of which is to heat the vessel to well above the right temperature and wait for the food to come up to the right temperature. The cooker linked takes advantage of this method since it is fine if the vessel comes down in temperature a little bit, so long as it doesn't get below the food's "done" temperature. You still have to be vigilant about the temperature of the food, to ensure it's not overcooked.

The less common method is to heat the vessel (often water) up to the right temperature, and let the food come to equilibrium. This is basically sous-vide, and would not work with the linked method, since the temperature of water can't go down. You might be able to fudge things a bit by over-heating the water a bit, but then you risk overcooking the food.

[lippel82]

Not all food is done once it reaches the desired temperature. A lot of food, e.g. tough meats, need to stay above a certain temperature for a long time until they're done.

[adrianmonk]

Or dry beans. Imagine if you just brought those up to temperature and skipped simmering for ~1-2 hours.

Or pasta. You don't bring the water to a boil and then immediately drain.

Or rice, similar to pasta.

Or some tougher leafy greens. Collard greens need to be simmered ~30-60 minutes.

Or caramelized onions. You are doing chemical reactions (browning sugar, etc.) that take time.

[k_sze]

Yep. It’s all just physics and chemistry.

There is a gradient of temperature from the surface to the inside of the food. Depending on the composition, it will take more or less time for the thermal energy to propagate.

In addition, cooking involves chemical reactions. Now, I’m not a biochemist, but if I had to guess, most cooking chemical reactions are probably endothermic (short of setting your food on fire), in which case the chemical reaction comes f cooking will remove thermal energy from your cooking medium (e.g. water or oil) and your cooking medium will cool down even if you had perfect insulation.

[falcolas]

Well, kinda? For example: smoking. You cook it for a long time at a low heat, but that's more about heating it up slowly as opposed to bringing it to a temperature and holding it there. And ultimately you (well, you're supposed to) gauge its doneness by its temperature; smokers still follow the "the vessel is hotter than your target heat" rule.

[jayd16]

I would think a slow cooker is a good example of sustained temperature making a big difference.

[grogenaut]

And to further that, there's a lot of state change happening at those temps, often why things hold at exact temps for a bit (eg boiling), so they can take plenty of energy to go up a tiny amount. Biscuit for instance has "the rest" at around 165-175. It also sweats a lot and cools itself off unless you wrap it.

[grogenaut]

Ugh spell check corrected Brisket to Biscuit. Not quite the same thing.

[falcolas]

Boiling something is more about pulling water out than it is finishing the food. But it's definitely one of the corner cases - for the reason you mention: the temperature increases are small.

But temperature for boiled things is still important - see candy for example. The temperature directly indicates the amount of water left in the mixture.

All that said, resting is a distinct step from heating that is often required for a food to end up as you expect it to. IWO, yeah, food isn't always ready to eat after heating.

[bagacrap]

counterpoint: sous vide