Vinegar is the end of a chain every fermenter knows: yeasts turn sugar into alcohol, then acetic acid bacteria turn the alcohol
into acetic acid. Leave kombucha or tepache too long and you’ve started it by accident.
Making good vinegar on purpose is mostly about the alcohol you start with, air, and warmth. The one thing you can’t easily do at home
is know how strong it is, and that decides what you can use it for.
Two Fermentations, One After the Other
Naturally made vinegar comes from the “sequential fermentation of sugar to alcohol and then to acetic acid”
(Penn State Extension). US labelling guidance defines cider vinegar the same way: made “by the alcoholic and
subsequent acetous fermentations of the juice of apples” (FDA).
- First, in the alcoholic fermentation, yeasts turn the fruit’s sugar into alcohol, with the jar closed to air. For cider vinegar,
use juice from autumn and winter apples; summer and green apples don’t have enough sugar (Ohio State University Extension).
A wine yeast speeds this up; bread yeast isn’t recommended (same source). If you already have hard cider or wine, this step is done. - Then, in the acetic fermentation, acetic acid bacteria (Acetobacter, Komagataeibacter and relatives) oxidise
the alcohol to acetic acid. They need oxygen, so this stage happens in a wide, open-topped vessel. Industry does it either at the
surface, the traditional slow way, or “submerged” with forced air; the choice changes the vinegar’s character
(Luzón-Quintana et al., 2021).
The Number That Decides Your Vinegar’s Strength
The acid you end up with comes from the alcohol you start with. NC State Extension puts the practical yield at about 120%: each gram of
alcohol gives roughly 1.2 g of acetic acid (NC State Extension). It also says wine at 11–12% alcohol must be diluted to
5.5–7% before it goes in. Worked through (alcohol by volume × 0.789 g/ml × 1.2):
| Alcohol you start with | Acetic acid you can expect, at best |
|---|---|
| 5.5% | about 5.2 g per 100 ml |
| 6% | about 5.7 g per 100 ml |
| 7% | about 6.6 g per 100 ml |
That’s at best, if every bit of alcohol converts and none is lost: weak cider or wine makes weak vinegar. For comparison, US labelling guidance expects vinegar to contain
4 g of acetic acid per 100 ml (FDA), and pickling recipes are built on vinegar of 5% acidity
(Penn State Extension). In one study comparing mango and papaya vinegars made this way with two shop vinegars, acetic acid ranged from 3.7 to 5.6 g per
100 ml (Bouatenin et al., 2021).
Method: Cider or Wine Vinegar
- Start with hard cider or wine at 5.5–7% alcohol. Dilute stronger wine with water: 500 ml of 12% wine plus 500 ml of
water is about 6%. - Use glass, stainless steel or enamel, never other metals or aluminium: the acid corrodes them
(Ohio State University Extension). Fill a wide jar about two-thirds full, so there’s a large surface in contact with air
(NC State Extension). - Add a vinegar culture. NC State recommends a bought “mother of vinegar” culture: just leaving wine open to the air
can work but is “very risky because some other organisms may grow” (NC State Extension). Live vinegar from a previous
batch, or raw vinegar with its mother, also carries the bacteria (same source; Cambray and Kalinski, 2025). - Cover it with a tightly woven cloth held with a band, so air gets in but flies don’t.
- Keep it warm and still. 80–85°F (27–29°C) is ideal; cooler or fluctuating temperatures slow it down and too hot
kills the bacteria (NC State Extension). Don’t move or stir the jar once the mother forms. - Wait 3–4 weeks, then taste a little from under the mother with a clean straw or spoon. It’s done when it tastes
sharp and sour and no longer smells of alcohol. - Bottle it full and close the bottles. Once ready, keep vinegar away from air, or the bacteria go on to break the
acetic acid down (same source). - If you like, strain out the mother and pasteurise the vinegar at 140–160°F (60–71°C) to keep it stable for a long time
(Ohio State University Extension); a few months of rest at 50–60°F (10–16°C) mellows its bite (NC State Extension).
The Mother of Vinegar
The slippery, pale disc that grows on top is a mat of cellulose made by acetic acid bacteria, mostly Komagataeibacter
species, the strongest cellulose producers among them (Gullo et al., 2018). In live cider vinegars sold with their mother,
Komagataeibacter was the dominant bacterium (Cambray and Kalinski, 2025). It’s the same kind of material as a
kombucha SCOBY. A healthy mother is smooth, rubbery and beige to translucent; it often thickens and sinks, and a new one forms on top.
Fuzzy, dry, coloured spots on top are mould: discard the batch (see our troubleshooting guide).
What Homemade Vinegar Is For, and What It Isn’t
- Use it for dressings, marinades, sauces, splashes into cooking, and flavouring.
- No: pickling, canning or anything stored at room temperature. “Because the acidity of homemade vinegars will vary, do
not use them in foods to be canned or stored at room temperature” (Ohio State University Extension); “do not use homemade
vinegar or vinegar of unknown acidity in pickling” (Penn State Extension). For quick pickles
and anything preserved, use shop vinegar labelled 5% acidity.
Measuring the strength takes a titration, not pH strips: pH tells you how acidic the vinegar is, not how much acetic acid it contains.
Acid test kits sold for winemaking work by titration. Even then, recipes for preserving are tested with commercial vinegar, so use that
for anything that has to keep safely.
If you make your own cider first, see our sidra natural guide for the alcoholic stage.