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Vinegar, Sugar
Take a sufficient quantity of water, and to every three quarts put a pound of raw sugar. Boil for half an hour, skimming if necessary. Set the liquor in an earthen vessel to cool; when not more than lukewarm throw in a slice of bread with yeast strewed over it thickly on both sides. Ferment for two days, then pour the liquor into a barrel which has previously been well rinsed out with vinegar. Paste over the bung-hole a piece of brown paper, perforate this with a fork, so as to leave little air-holes, and set the barrel in a dry, warm place.
This is a two-stage ferment: yeast turns the sugar solution into a weak alcohol, then airborne Acetobacter turns the alcohol into acetic acid. The recipe as printed leaves out most of the second stage, which is where the time and the attention actually go.
- The hinge: air, then patienceThe perforated paper is not decoration. Acetobacter needs oxygen to convert alcohol to acid, so the vessel must be loosely covered against insects but never sealed. Fermenting to a usable vinegar takes two to six months at 20-30C, not the two days the recipe names for the yeast stage.
- Quantities and unitsA pound of sugar to three quarts of water gives roughly 13% sugar by weight, which could ferment out to something in the region of 6-7% alcohol before the acetic stage begins. If the book's quarts are imperial (40 fl oz), the syrup is slightly weaker than with US quarts (nearer 16%); the difference is not material here.
- Raw sugarVictorian raw sugar was unrefined or part-refined cane with molasses still in it, which carried trace nutrients useful to the yeast. Turbinado, demerara or another unrefined cane sugar is the closer match; a ferment on plain white granulated may be slower for want of those nutrients.
- The bread and yeastThis is a delivery method for the yeast, not a sourdough step. A quarter-teaspoon of active dry yeast stirred straight into the lukewarm liquid does the same job; lukewarm means roughly 30-35C, and water much hotter than about 40C stresses the yeast, with temperatures near 50C killing it.
- VesselA rinsed barrel supplied the resident acetic bacteria that started the second stage. Without one, use a wide glass jar or crock, cover with muslin, and add a few tablespoons of unpasteurised live vinegar or a piece of vinegar mother to inoculate it. Avoid reactive metal throughout.
- Warm and dark"A dry, warm place" means steady warmth, roughly 20-30C, out of direct sun. Cold stalls the bacteria; above about 35C they suffer.
- Yield and strengthThree quarts of syrup gives a little under three quarts of vinegar. Its acidity is unknown and untested, and cannot be assumed to reach the 5% of commercial vinegar, so treat it as a table and cooking vinegar only. Do not use unmeasured homemade vinegar for pickling or any preserve that relies on acidity for safety.
Vinegar was a household staple that a large kitchen might reasonably make itself from whatever cheap sugar or fruit surplus was at hand. British vinegar was traditionally malt-based, the by-product of brewing, while wine countries made theirs from wine; sugar vinegar was the improviser's version, needing no grain mash and no grapes. The insistence on rinsing the barrel with vinegar first, and on the perforated paper over the bung-hole, shows a working grasp of the process well before Pasteur's account of acetic fermentation in the 1860s was general knowledge: brewers and housewives knew that a used vinegar cask seeded the next batch and that air had to reach the liquor. Suspicion of bought vinegar also mattered. Nineteenth-century public-health writing repeatedly accused vinegar dealers of sharpening weak stock with sulphuric acid, and a domestic supply of known origin was a defence against that.