Smash blueberries and place in a large glass jar. You can also smash the blueberries after you add them to the jar.
Add vinegar.
Stack basil leaves, then roll together lengthwise. Crush lightly in your hand, then add to the jar. Place a lid on the jar then shake it well. Store in a dark cool place for 3-4 weeks. Shake jar at least once per week.
After 2 weeks, you can begin tasting the vinegar. Once it reaches your taste preference, the vinegar is done and can be strained.
Strain vinegar into a fine sieve. Do not push down on berries or mixture or the vinegar will become cloudy.
Place strained vinegar in clean, sterilized jars. Store in a dark cool place or in the refrigerator.
Notes
Before using your vinegar, look at the bottle. If it has any mold or shows signs of fermentation, such as bubbling, cloudiness, or sliminess, discard the product and do not use any of it that is left.