Eli5: why boiling food makes it soggy but deep frying makes it crispy?
In: 6
Food contains water, I hope. When you boil it, the energetic water molecules break down the food and let even more water penetrate. I don’t know about you, but I was happy with the amount we had before. So this extra moisture makes things soggy – it’s literally chock full of all the water it can possibly hold, like a sponge.
In contrast, deep frying vaporizes the water already inside the food. Suddenly your crab cake or potato is filling with its own steam, the pressure growing every moment.
That steam would of course love to abscond into the surrounding atmosphere, yet unfortunately it’s surrounding by boiling oil. We all know from grade school that water and oil are [immiscible](https://en.wikipedia.org/wiki/Miscibility), it would take time and energy to have the steam pass through.
We don’t want to give it that time. Instead we fry just long enough to keep the steam trapped inside. Instead of escaping it then turns the food into a deliciously crispy fortress.
Carbohydrates deep fry best, things like gluten or starches in potatoes. The long chains of the carbohydrates link together, and then are shaped by expanding gasses like bubbles or balloons. The water vapour hides inside these as best it can.
That’s how deep frying can produce moist but also crunchy foods. It’s just water following the rules- how to exist while using as little energy as possible. The answer, as in most things in physics when you get right down to it, is [entropy.](https://en.wikipedia.org/wiki/Entropy)
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