It is important to use the highly acid wine vinegar/or this sweet berry vinegar because it becomes so diluted by the berry juice. Without enough acidity, the end product could spoil; don’t be tempted to use ordinary white vinegar. The high-acid vinegar is available in specialty and gourmet food stores.
Combine berries with sugar and place in jars. Fill with vinegar, apply lids, and process for 10 minutes in a boiling-water bath. Let sealed jars cool, then refrigerate for 3 weeks; then strain and bottle. Use on fruit, in salads, in marinades, and as a sauce component, especially for chicken and duck livers. It’s also nice, with sugar, as a light dressing for fresh strawberries.