Heat the vinegar and geranium leaves in a nonreactive saucepan until hot but not boiling. Place the raspberries in a widemouthed quart (or larger) jar and crush lightly with a wooden spoon. Pour in the hot vinegar and geranium leaves. Cover the jar with plastic wrap and secure with string or a rubber band. Season for at least 2 weeks in a cool, dimly lit place, swirling contents occasionally. Strain the vinegar through a sieve lined with 2 layers of dampened cheesecloth into a sterilized bottle. Drop in the fresh raspberries and fresh geranium leaf. Cap or cork the bottle.
Makes 1 quart.