In medium jar, place berries and vinegar. Seal jar and let stand in a sunny window for 3 to 4 days or until vinegar takes on a bright red color. The berries will soften and loose their color. Strain mixture into a 1 quart saucepan (stainless steel) or enamel pan. Discard berries. Stir in sugar and heat to boiling. Simmer over low heat 10 minutes. Cool vinegar mixture and pour into a pint bottle. Seal and store in a cool, dry place or in refrigerator.