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Plum Vinegar
For two quarts of plums allow a gallon of water and let stand twenty-four hours. Add one-half pint sugar for each gallon of liquid; place in barrel in warm place (where it should be shaken each day while fermenting.)
This is a two-stage ferment compressed into three sentences: the plums and water become a weak sugar wash, then wild yeasts and acetic bacteria turn it to vinegar. The original gives no times beyond the first day and no test for doneness, so most of the work is filling in what the writer assumed every household knew.
- The measurementsTwo quarts of plums is roughly 3 lb of fruit, halved and stoned or at least well crushed so the juice can leave the flesh. "One-half pint sugar" is a volume measure, about 1 cup or 7 oz, per gallon of liquid.
- Read "barrel" as any large open crockThe barrel here is a container, not a requirement. A food-grade plastic bucket, glass jar or stoneware crock holding half again as much as your liquid works; you need headroom for the froth.
- Cover, do not sealAcetic fermentation needs air. Cover with cheesecloth or a tea towel against fruit flies and leave it loose. A sealed lid gives you alcohol and pressure rather than vinegar, and a closed jar of active ferment can burst.
- "Warm place" means about 70-80FBelow 60F the ferment stalls; much above 85F and the flavour coarsens. A kitchen cupboard or the top of a refrigerator will do.
- Give it a cultureThe recipe relies on wild bacteria on the plum skins, which makes results unpredictable. A few tablespoons of raw, unpasteurized cider vinegar per quart, stirred in once the vigorous yeast fermentation has slowed, makes the outcome far more reliable.
- The missing timelineExpect one to two weeks of active bubbling, then four to eight weeks of quieter souring under the cloth, stirring or shaking daily as instructed. Strain out the fruit once the bubbling stops; leaving pulp in for months invites mould rather than vinegar.
- Do not use it for canning or picklingHomemade fruit vinegar is usually well under the 5 percent acidity that preserving recipes assume, and the strength here is unknowable without a titration kit. Treat it as a dressing and finishing vinegar; use commercial vinegar for anything that must be shelf-stable.
- YieldRoughly the gallon of water you started with, give or take, once the fruit is strained and some liquid is lost to evaporation. Bottle in glass, cap loosely at first, and keep it out of direct light.
Vinegar was a way of using fruit too soft, too small or too plentiful to preserve whole — windfalls, bruised plums, the pickings after the good fruit had been canned. The word itself comes from the Old French vin aigre, sour wine, and the process is the same for plums as for grapes: yeast turns sugar to alcohol, then Acetobacter turns alcohol to acetic acid. Before commercial white vinegar was cheap and universal, a household that pickled, made salad dressing and cleaned with vinegar had good reason to keep a crock going, and fruit vinegars carried a flavour that distilled vinegar does not. The vagueness of the instructions is telling: fermentation was judged by smell and taste rather than by clock or hydrometer.