Vinegar

Why this method

Vinegar is made in two stages by two different organisms. First an alcoholic (anaerobic) fermentation: yeast converts sugar to ethanol and CO₂. Then an acetous (aerobic) fermentation: acetic-acid bacteria of the genus Acetobacter oxidize that ethanol to acetic acid, using oxygen pulled from the air. The gelatinous cellulose biofilm that forms on the surface is the mother of vinegar — a raft of bacteria and cellulose, not the active agent itself but a convenient carrier you can pass to the next batch. The reaction is roughly 1:1 by strength: about 1% ABV yields about 1% acetic acid, so the starting alcohol sets your ceiling.

Parameters

Parameter	Value
Sugar source	fruit juice, cider, wine, or sugar water
Yeast stage	anaerobic, 18-24°C, days to weeks, to ~5-8% ABV
Starting alcohol for acetification	5-8% ABV (dilute wine/spirits down to this)
Acetous stage	aerobic, 21-27°C, 3-6 weeks
Inoculum	mother of vinegar or raw unpasteurized vinegar (10-20%)
Table-vinegar endpoint	≥ 4% acetic acid
Canning-use endpoint	5% acetic acid

Equipment

• Wide vessel (crock or jar) — surface area drives the aerobic stage
• Breathable cloth cover and band (excludes flies, admits air)
• Mother of vinegar or a bottle of raw, live vinegar as inoculum
• Titration kit or acidity test strips to confirm the endpoint
• Calibrated pH meter

Method

Make or supply the alcohol

Ferment a sugar source to 5-8% ABV with wine yeast, or start from cider/wine. If using a strong wine or spirit, dilute with non-chlorinated water to 5-8% ABV — above ~10-12% the Acetobacter stall.

Inoculate for the acetous stage

Pour the alcohol into a wide vessel, leaving plenty of headspace and surface. Add 10-20% raw live vinegar or a mother of vinegar. Cover with breathable cloth so air gets in but flies stay out.

Acetify aerobically

Hold 21-27°C, undisturbed, for 3-6 weeks. A new mother forms on the surface; do not break it. The smell shifts from alcoholic to sharp and acetic.

Confirm the endpoint by acid, not taste

Titrate. Stop when acidity reaches at least 4% acetic for table use, or a full 5% acetic if the vinegar will be used in any canning or pickling recipe.

Strain, bottle, and (optionally) pasteurize

Strain out the mother, reserving some for the next batch. To stabilize and stop further change, hold at 60-71°C / 140-160°F for ~10 min before bottling; otherwise store cool and dark.

Caution

Acidity is the safety control for any canning use. Use only vinegar tested at 5% acetic acid for water-bath/acidified pickling, and never dilute the acid in a tested recipe. Home vinegar of unknown, unverified strength must not be used to acidify canned foods — measure it first, or buy commercial 5% vinegar for canning. See Titratable Acidity and Safety and Botulism. Low-acid foods are never made safe by adding vinegar alone; this site refers pressure canning out.

Note

A thin, gelatinous, layered raft on the surface is the mother and is desirable. Fuzzy, raised, colored mold is not — discard a batch with blue/green/black fuzz. Vinegar eels (harmless nematodes) sometimes appear in live vinegar; pasteurization removes them.

Tip

Keep the vessel wide and shallow: acetification is oxygen-limited, so surface area, not volume, sets the speed.

⚗️ Confirm the acid endpoint

🛡️ pH safety calculator

See also

• Titratable Acidity — measuring % acetic and the 4% / 5% windows
• Kombucha — the same ethanol-to-acetic chemistry, stopped earlier
• Aerobic vs. anaerobic — why the two stages need opposite conditions
• Safety and Botulism — vinegar strength in canning