What causes frying something to be crispy as opposed to boiling it?
In: 2042
Water boils at 100degrees Celsius.
Your water in the pot is slightly below this temperature, so really, you are soaking your food in hot water.
This causes the food to absorb more water.
Absorbing more water tends to make things soft.
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Oil can go higher than 100 degrees Celsius.
The oil in the pot is above the boiling point of water, so it gives it’s heat to the food, and the water turns to steam and leaves the pot (as bubbles of water vapour->steam).
This causes the food to get drier, especially on the outside where it is touching the oil.
Becoming dry tends to make things harder, and the expanding bubbles of gas tend to leave little spaces behind, giving a ‘crisp’ feel, where it is rigid and hard, but breaks easily due to being thin/brittle.
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(If things get drier without this frying effect, then things tend to get cruchy or just solidly hard, like when you cook something for a long time in the oven. Consider baking bread, or the outside of a long-cooked roast, or overcooking biscuits/cookies. However, there are other ways to get things crispy than just frying, so other techniques can also get something baked in an oven to be crispy. However frying in oil tends to more easily make things crispy.)
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