Ask Shanghai-based chef Lucas Sin how to prepare a fluffy sweet potato and he'll lead you to the freezer. In Hong Kong, where he was raised, the root vegetable is a favorite street snack. People often freeze sweet potatoes and, depending on their size, let them slightly defrost before roasting. The result is a fluffy center and a carmelized, paper thin skin. Purple and orange-fleshed sweet potatoes have a higher sugar content so they make the best candidates for the freezer-to-oven method.
In China, you'll find sweet potatoes roasted on the street in woks filled with pebbles and charcoal. In Dongbei, people leave pears outside to freeze, bring them in to defrost, then place them outside to re-freeze. "While that's happening, the skin will turn slowly from white to black as it oxidizes," Sin says. "But because the skin is intact, all of those juices are trapped inside, and the best way to eat it is basically to peel a little bit of that now leathery skin off and just sort of suck all the juices out of the pear."
On the savory side, when firm tofu freezes then hits a hot pot or stew, the crystallized water in the frozen tofu melts and leaves holes that act as a sponge, allowing all the flavor of a broth to be absorbed.