In a 4- to 6-cup widemouthed jar, combine sake and pineapple or mango. Cover and chill until sake has a subtle fruit flavor, about 5 days. Lift out fruit with a slotted spoon and discard. Serve cold--the sooner, the better. Leftover sake (without fruit) will keep up to 1 week when stored airtight in the refrigerator.
Servings Makes about 6 servings