Why is it that when you cut a bagel in half and toast it the outside part is WAY hotter to the touch than the inside?
In: Chemistry
What does it mean something feels hot? It means it transfers a lot of heat energy to your fingers.
This means you need a high temperature for fast transfer, and a mass comparable to your finger so that the energy is significant. (For example, a little speckle of burning oil may sting you a little, but it’s so small that the total energy isn’t significant enough to cause a burn.)
Now, for the bagel. Toasted (dried) bread is an awesome heat insulator. It is a solidified foam with most of the volume being air (which is an insulator). This means that when you touch it you only interact with the very top layer of the bagel, everything deeper underneath is isolated from your fingers. Effectively, the mass of the bread that can transfer heat to your finger is very tiny.
The crust is solid. It’s mostly carbon. Carbon is a great heat conductor. So, touching hot crust means taking the heat of a significant mass of the crust (the deeper layers will transfer heat effectively towards your fingers).
Bagels are specifically made so that the outside is very smooth. They’re boiled before baking and often brushed with an egg wash. Both these processes can also make them slightly sticky, especially when they’re hot. Meanwhile, the inside is rough and porous. When you touch the inside, a lot of what you’re “touching” is pockets of air, which don’t do a good job of transferring heat. When you touch the outside, you’re mostly touching bagel, which does a much better job of transferring heat. The outside may also stick to your hand a little longer than you’d like it to, so you can’t draw it away immediately after realizing it’s too hot.
tge outside is a smooth solid shell which will absorb all the heat. the inside is porous, full of holes and spaces that let the heat absorb and spread out more beyond the surface, with the added spaces for air movement.the inside will stay cooler.
place a black piece of paper outside next to a black piece of mesh the paper will be hotter because the surface is solid.
The sides of the toaster are hotter than the middle, and the outside crust of the bagel is super thin, not as dense as bread. :^)
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