A bubbly cocktail made with a rhubarb shrub (drinking vinegar).
Combine the rhubarb, sugar, salt, and mint in a jar. Stir to combine. Seal the jar and let the mixture sit at room temperature for 3-5 hours. Then put the jar in the refrigerator.
The next day, add the vinegar to the jar, stir, and return the jar to the refrigerator. Keep the jar in the refrigerator for 2-3 days.
Remove the jar from the refrigerator, strain out the rhubarb, and your shrub is ready to use for cocktails.
Pour about 1/4 cup of the shrub into each of six cocktail glasses. Add ice. Then divide the tonic water evenly among the glasses, and do the same with the wine, if using it. Stir and serve immediately.
The shrub may stay in the refrigerator for up to a month.