Recipe Homemade Rhubarb Vinegar

INGRÉDIENTS

1 cup (250 ml) rhubarb, washed and chopped, at room temperature (fresh or frozen rhubarb)
3 or 4 juniper berries (for the yeast on their skins)
1/4 cup (60 ml) Uncle Berwyn's Pure Yukon Birch Syrup, at room temperature
4 cups (1 L) water at room temperature – if using tap water, let stand for a few hours to allow the chlorine to evaporate

PRÉPARATION

Place the rhubarb in a bowl deep enough to allow vigorous stirring and wide enough to allow maximum exposure to air. A 2 L mixing bowl will do the trick.
Dissolve the birch syrup in the water and pour over the rhubarb.
Stir vigorously and cover with cheesecloth held in place with a rubber band or string.
For the next week, stir vigorously every 2 to 3 hours.
After a few days, the mixture should start to bubble into small, fizzy bubbles that collect at the edge of the bowl. You might see some white yeast forming on the surface. Don't worry about the yeast; it's not a bad thing, but it may require more vigorous stirring.
If mold starts to form, scrape it off with a spoon. (I tasted the vinegar every other day. At first, it tasted like birch syrup. After about three days, it took on a tangy flavor that eventually became both hot and sour.) After a week to 10 days, strain the mixture and discard the rhubarb. Return the strained liquid to the cleaned bowl or a screw-top jar. Cover with cheesecloth. Continue stirring or shaking vigorously (put the lid on the jar before shaking, and remove it afterward) for three or four days. Taste your vinegar. If you're happy with its tartness and acidity, stop the show! Cover the jar and refrigerate the vinegar.
I was happy with mine after 2 weeks, although in Wild Fermentation, Sandor Katz indicates that fermentation typically takes 3 to 4 weeks.