1 litre of jamun juice A sterilised glass jar or ceramic or a new earthen pot
Pour the jamun juice in the pot. Tie the mouth of the jar with a clean muslin and then cover, allowing the passage of air. Keep the jar on a sunny window for about three months.
You can open the jar and smell the vinegar forming in between, the aroma of the vinegar will be the best indicator of ready vinegar but the best visual sign is when the layer of the microbes on the surface makes a stable disc that does not break when you lightly stir the liquid inside.
Strain the vinegar after three months in a sterilised bottle. Store in a cool dark place and use it for making vinegar onions or for salad dressing or just have it in a small shot glass every day for probiotic supplementation.