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Grape Vinegar
For this use wild grapes, pressing out juice, boiling down till one-half the original quantity. To three-fourths barrel add three gallons of molasses; put in a warm place to ferment, after which close the bung.
This is a barrel-scale recipe written for a farm cellar, and it assumes a great deal of knowledge that the author did not think worth writing down. The hinge is air: sugar first ferments to alcohol, and only then does exposure to air turn the alcohol to acetic acid. Closing the bung too soon leaves you with sour wine rather than vinegar.
- How much a barrel isA standard American barrel of the period is about 31 to 32 gallons, so three-fourths barrel is roughly 24 gallons of reduced juice, with 3 gallons of molasses added. That is a ratio of about 8 to 1, which scales cleanly: 1 gallon juice to 2 cups molasses.
- Wild grapesThese are riverbank, fox or frost grapes (Vitis riparia, V. labrusca and relatives) -- small, seedy and sharply acid, and generally lower in sugar relative to their acid than table grapes, which is why the recipe adds molasses for fermentable sugar. Concord or other slip-skin grapes are the closest supermarket substitute.
- MolassesUse unsulphured cane molasses. Blackstrap is the last boiling, less sweet and with a bitter mineral edge that carries straight through into the finished vinegar.
- Boiling down by halfThis concentrates both sugar and acid and drives off water; it also pasteurises the juice, killing the wild yeasts on the skins. Expect to add yeast, or a splash of active fermenting must, to get things started.
- A warm placeAlcoholic fermentation wants roughly 65-75F; acetic fermentation wants 75-85F and slows badly below 60F. In an unheated cellar the process could stall for months, which is why the original specifies warmth rather than a cool store.
- Air, then the bungDuring souring the vessel should be loosely covered with cloth, not sealed, and only about two-thirds full so there is surface area for the acetobacter to work. Adding a little raw, unpasteurised vinegar with a live mother speeds this enormously. The bung goes in only once the vinegar tastes finished, to stop it oxidising further to flatness.
- VesselsWood, glass or food-grade plastic only. Acetic acid attacks copper, brass, galvanised metal and old glazed crocks of unknown provenance; a lead-bearing glaze is a real hazard with something this acidic.
- Testing the strengthHome vinegar of this kind commonly lands between 3 and 5 percent acetic acid, and there is no way to know without titration or test strips. Treat it as a table and salad vinegar. Do not use untested homemade vinegar for pickling or canning, where 5 percent is the assumed baseline for safety.
- Time and yieldReckon on two to six months from start to usable vinegar, depending on temperature. Wild grapes are small, seedy and comparatively low-yielding, so a modest batch takes a great deal of fruit.
Vinegar was often a household manufacture rather than a purchase in the nineteenth century: it preserved the cucumbers, the beets and the walnuts, and farms with an orchard or a fencerow of wild vines might make their own from whatever was cheapest. Wild grapes were free for the picking across much of the eastern United States, and too acid and pippy to be worth much as dessert fruit, so they went to jelly, to unfermented "grape juice" and to vinegar. The molasses here is doing the work the grapes cannot -- supplying enough sugar to make the alcohol that the acetobacter will later eat -- and it suggests a kitchen where molasses was a cheap standby sweetener alongside granulated sugar. The instruction to "close the bung" is the whole of the author's storage advice, which tells you how routine the process was assumed to be.