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Comment by 0xcde4c3db | Hacker News Reader

> Microwave ovens do not cook food from the inside out. 2.45 Ghz microwaves can only penetrate approximately 1 centimeter (0.39 in) into most foods. The inside portions of thicker foods are mainly heated by heat conducted from the outer portions.

I think the main reason this myth persists is stuffed/filled food items such as pizza rolls, burritos, Pop Tarts, Hot Pockets, etc.. With these, there's typically an outer layer that is thermally insulating and lower-density, while the filling is more thermally conductive and higher-density (water/fat). This means that even if the temperature is uniform, the filling will be perceived as much hotter than the outer layer.

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Microwaves work by heating the polar molecules in liquid solution, which essentially means water in food. If you've got food with some kind of crust, the crust tends to be dehydrated. Consequently, the crust doesn't get much heating, particularly when compared to the internal melange.

In that vein, it's not really wrong to say that the food is cooked from the inside out, so long as you don't understand to mean that it is literally cooked from the exact middle. The heating is still coming from the interior which is conducting heat to the exterior shell; that's it the outermost layers of the interior filling that's heating, not the innermost layers, is a minor detail by comparison.

I think, more practically, it's that this characteristic of heating is in stark contrast to traditional ovens, which are very much exclusively outside-in, no matter the composition. That is, "cooking inside out" is useful as a heuristic even if, pedantically, a misconception.

I routinely use a microwave to pre-heat the inside [1] of something before finishing it off in an oven or toaster oven (sometimes in convection mode). That way, I gain the vast majority of the benefit of speed from my high-powered microwave along with the mouthfeel and caramelization benefit of the traditional oven.

The contrast can be particularly stark (and useful) when working at temperatures above boiling.

I once ended up convincing my Mom into using the "cooking the inside" heuristic of a microwave in order to save an apple Charlotte that came out with uncooked dough in the center [2]. It took a few single-minute zaps to get it there, but it worked great.

[1] Well, of course, the whole, but it's the inside that's important for this exercise

[2] She was quite distraught because she'd never had that failure in the dozen-plus times she'd made the cake previously. Despite being a veteran of the semiconductor industry, she suspected herself first instead of the oven hardware, which it turned out to be.

That and water is very good at storing heat meaning that it stays skin blisteringly hot even after the rest of the food has cooled down to edible levels.

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