French fries are one of the world's most delicious foods, unless they're cold. Then they're like salty drywall. Why does that happen?

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A chemistry professor from American University in Washington D.C. finally has the answer for you. It all has to do with the starch in the potatoes.

"Starches taste good when they are 'hydrated,'" said Matt Hartings. "Think of the starches in potatoes as tiny crystal spheres. At really high temperatures (like in fryers), water will go into those spheres and fill them up like balloons. Instead of a small, hard sphere, you end up with something more 'poofy.'"

When French fries are hot, the starch inside is retaining water, which makes them taste great. Once they cool down, that water evaporates and the taste goes with it.

Smell also plays a huge part: "Fresh french fries have a great aroma, but when they're cold, the smell is largely gone," Hartings said. "Without that smell, a lot of the flavor disappears."

Read more at LiveScience.