The reason for this behavior is actually much more interesting than you might think!

Raccoons have the most sensitive sense of touch of any animal known other than primates. Over two thirds of the sensory processing power of a raccoon's brain are dedicated to its sense of touch, while the critter's tiny hands are packed with over ten times the number of nerve endings as a human hand.

These very sensitive hands develop a thin protective barrier over time- sort of like a callous— but the layer is softened by water.

When a raccoon dips its hands into water, it can feel with perfect acuity. A raccoon will explore its food, memorizing and savoring its texture to learn about it and to be better able to identify and search for it in the future.

In French, they are called "washing raccons". I don't even know any other kind of raccon.