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Rhubarb Vinegar
For five gallons take about fifteen ordinary stalks of rhubarb. Wash and pound or crush it with a potato masher in the bottom of a strong tub, then add five gallons of cold water, cover and stand aside twenty-four hours. Strain off, and add eight pounds of brown sugar, and a cupful of good yeast or one compressed yeast cake dissolved in a cup of lukewarm water. Stir till the sugar is dissolved, then stand in a warm place over night. In the morning put in a ten-gallon cask, place where the temperature will not fall below 60°. In a month strain off the grounds, return to the cask again and let stand until it becomes vinegar, perhaps two or three weeks.
A two-stage ferment: yeast turns the sugared rhubarb water into a weak wine, then airborne Acetobacter turns the alcohol into acetic acid. The recipe assumes a household that already knew the second stage happens on its own, and skips the conditions that make it happen.
- Air is the hingeThe yeast stage wants to be covered and quiet; the vinegar stage needs oxygen. A cask bunged tight will sit as sour cider indefinitely. Cover the vessel with cloth secured against fruit flies and leave plenty of headspace once the primary ferment has slowed.
- Scale it downFive gallons is a Victorian quantity. The proportions reduce cleanly: roughly three stalks of rhubarb, one gallon of water and 1 lb 10 oz brown sugar per gallon of finished liquid. A gallon jar with a cloth cover is a more realistic vessel than a ten-gallon cask.
- Rhubarb leavesUse stalks only. The leaves carry oxalic acid at levels high enough to cause harm and should never go into the tub, however much bulk they add.
- "A cupful of good yeast"This means liquid barm skimmed from a brewing or bread ferment. A modern compressed cake is about 0.6 oz, though period cakes varied in size; in practice a teaspoon of active dry yeast per gallon, or a wine yeast for a cleaner ferment, will do the job, which is rather more yeast than the original proportion.
- TemperatureThe 60F floor is for the yeast. Acetobacter works fastest between about 80 and 85F, so the vinegar stage will run far slower in a cool room than the "two or three weeks" suggests -- expect months rather than weeks without a warm spot.
- Seeding the vinegarThe original assumes wild acetic bacteria will arrive on their own, as they would in a house that had made vinegar before. A modern kitchen is far less likely to carry a reliable population. Adding a few tablespoons of raw unpasteurised vinegar, or a mother, per gallon makes the difference between vinegar and a jar of mould.
- Strength is unknownEight pounds of sugar in five gallons is a fair amount of sugar, but how much of it ferments and how completely the alcohol converts is out of your hands, so the finished acidity is unpredictable. Do not use this for pickling, water-bath canning or any preserving unless you have tested it and it reaches 5 percent acetic acid. As a table and dressing vinegar it is fine.
- FinishingStrain, bottle and let it settle. It will keep at room temperature; pasteurising at 150F for half an hour stops it developing further and prevents a new mother forming.
Rhubarb was a cheap and enormously productive garden crop in nineteenth-century Britain and North America, cropping in spring before anything else was ready, and cookbooks of the period strain to find uses for the glut beyond pies and preserves. Vinegar was the obvious one: a household that made its own could turn almost any sugary or acid plant waste into a year's supply, and recipes for vinegar from cider, malt, beet, maple sap and rhubarb sit side by side in the domestic manuals. The technique is older than the understanding of it. Households worked by inheritance, keeping a cask that had made vinegar before and so carried the bacterial culture in its wood, which is why the instruction here can end so casually with "let stand until it becomes vinegar." That the souring is the work of a specific bacterium, rather than an inevitable spoiling, is generally traced to Pasteur's work in the 1860s, though the practical craft long predates it.