In a glass jar with a non-reactive lid, combine the berries and the vinegar. Seal the jar and let the mixture stand for 3 weeks, preferably in the sunlight, which will help to draw out the fruit juices.
After 3 weeks, strain the vinegar into a large saucepan through a double layer of dampened cheesecloth. Boil over high heat until it is reduced by one-fourth.
Ladle vinegar into warm, sterilized jars and seal.
Raspberry vinegar may seem an extravagance, but it can be made in 2 simple steps with 2 ingredients. This is an ideal use for very ripe, extra soft or slightly squashed berries, but perfect berries will work, too.
