Cider vinegar from scraps
Turn apple cores and peel into real cider vinegar. The two-stage ferment explained (alcohol first, then acetic) with timings, visual cues, and why it is never safe for canning.
What you'll need
- A wide-mouth glass jar or ceramic crock Wide is the point. Acetic fermentation needs surface area and air, which is the opposite of every other ferment on this site. A half-gallon jar suits the scraps from about six apples.
- Apple scraps (cores, peels, or whole bruised fruit) Roughly enough to fill your jar two-thirds. Unwaxed and unsprayed if you can; the wild yeast lives on the skin. Windfalls and bruised apples are ideal.
- Plain sugar White, cane, or brown. This feeds the yeast in stage one. Honey works but ferments more slowly.
- Unchlorinated water Filtered, bottled, or tap left uncovered overnight. Chlorine is designed to kill microbes and will stall the ferment.
- A tightly-woven cloth and a rubber band Not a lid. Air must get in, fruit flies must not. A doubled square of muslin, a coffee filter, or a clean tea towel all work.
- pH strips or a titration kit Optional but the only way to know what strength you finished at. Strips are cheap and adequate; titration is exact.
TL;DR
Fill a wide-mouth jar two-thirds with apple scraps. Cover with sugar water (1 tablespoon of sugar per cup of unchlorinated water) until everything is submerged. Cover with cloth, not a lid. Stir daily for 1 to 2 weeks until it smells like cider and stops bubbling. Strain out the solids, return the liquid to the jar, re-cover with cloth, and leave it alone for 3 to 6 weeks at 65 to 80°F.
It is done when it smells sharply of vinegar, tastes cleanly sour with no alcoholic heat, and reads pH 2.5 to 3.5.
The one rule that separates this from every other guide here: this ferment needs air. Do not seal the jar.
Two ferments, not one
Vinegar is the only two-stage ferment on this site, and almost every failure comes from not knowing that.
Stage one is alcoholic. Wild yeast, living on the apple skins and drifting in from the room, eats the sugar and produces ethanol. This is the same process that makes cider, and it is anaerobic-ish: the yeast tolerates air but does not need much of it. It is fast, visibly bubbly, and takes one to two weeks.
Stage two is acetic. A different organism, Acetobacter, oxidizes that ethanol into acetic acid. This one is strictly aerobic. It cannot work without oxygen, which is why the jar stays wide and open under cloth. It is slow, nearly invisible, and takes three to six weeks.
If you seal the jar, stage one happens and stage two never does. You get flat, weak cider. If you skip the sugar, stage one has nothing to work with, and there is no alcohol for stage two to convert, so you get sour apple water that spoils rather than preserves.
This is also why vinegar is the natural end of several other ferments. An over-sharp kombucha, a forgotten ginger bug, a bottle of cider left open: all of them already contain alcohol or acid and are one Acetobacter colony away from being vinegar. Nothing is wasted; it just moved down the line.
The conditions
Four variables, in order of how much they matter:
- Air. Wide surface, cloth cover. Surface area drives the rate of stage two more than anything else. A wide bowl converts faster than a narrow bottle holding the same volume.
- Sugar. About 5 percent, or a tablespoon per cup of water. This sets the alcohol level, and the alcohol level sets your final acidity. Too little sugar and you cannot reach a useful strength.
- Temperature. 65 to 80°F. Acetobacter prefers the warm end of that; below 60°F conversion crawls. Above 85°F you risk solvent off-flavors.
- Darkness. Not critical, but UV degrades the culture. A cupboard or a shaded counter is better than a sunny windowsill.
Fruit quality matters less here than in any other ferment. Bruised windfalls, the cores left from a pie, the peel from a batch of apple sauce: all of it works. What matters is that the fruit is unwaxed, since supermarket wax coats the skin where the wild yeast lives, and ideally unsprayed.
Step by step
1. Fill the jar. Apple scraps to roughly two-thirds. Cores, peels, whole bruised apples quartered. Do not pack tightly; the liquid needs to move.
2. Mix the sugar water. One tablespoon of sugar per cup of unchlorinated water, stirred until dissolved. Make enough to cover the scraps with an inch to spare; for a half-gallon jar, about 4 cups.
3. Pour and submerge. Everything under the liquid. Fruit above the waterline is where mold starts. A small glass weight or a clean saucer helps; so does a fermentation weight if you already own one from vegetable work.
4. Cover with cloth. Tightly-woven, banded on. This is the step people get wrong by reaching for a lid out of habit. Fruit flies find vinegar ferments from remarkable distances and will lay eggs in an uncovered jar.
5. Stir daily for 1 to 2 weeks. Once a day, push the floating scraps under and give it a swirl. You should see bubbling within two to three days and smell cider by the end of the first week. When the bubbling slows and the smell is clearly alcoholic, stage one is finished.
6. Strain. Remove all solids through a sieve or cloth. Squeeze them out and compost them. Return the liquid to a clean jar (wider is better) and re-cover with cloth.
7. Wait 3 to 6 weeks. Do not stir. A pale film may form on the surface: that is the mother, and it is what you want. Start tasting at week three.
8. Bottle. When it tastes right, decant into bottles with tight lids. Leave the mother behind in a splash of vinegar to start your next batch, or discard it.
Reading the surface
The surface of a vinegar ferment is the whole diagnostic panel, and three different things can appear there:
- A mother: smooth, pale, translucent becoming cream, flat and skin-like. Sometimes several stacked layers. This is the goal.
- Kahm yeast: flat but wrinkled or crinkled, dull white, sometimes patchy. Harmless. Skim it and carry on.
- Mold: fuzzy, raised, and colored: green, blue, black, pink. Discard the batch. Do not skim and hope.
The distinction between the first two is texture, not color; the distinction from the third is that mold has height and fuzz. Kahm yeast vs mold covers the visual call in detail, and it is worth reading before your first batch rather than during it.
When is it done, and how strong is it?
Taste is the practical test. Finished vinegar smells sharp and clean rather than fruity or alcoholic, and tastes sour without any warming, winey edge.
Measurement is the honest test. pH strips should land around 2.5 to 3.5. That confirms it is acidic; it does not tell you the acetic acid percentage, which is what commercial vinegar labels mean by “5%”. Getting that number requires titration, and even then it varies from batch to batch.
Which leads to the one genuine safety limit for homemade vinegar.
Do not use homemade vinegar for canning. Water-bath canning and shelf-stable pickle recipes are engineered around vinegar standardized at 5 percent acidity. That standardization is the safety margin. Homemade cider vinegar commonly finishes between 3 and 5 percent, and you cannot verify where yours landed without equipment most kitchens do not have.
Homemade vinegar is excellent in dressings, drinks, marinades, braises, sauces, and refrigerator pickles eaten within a few weeks. For anything sealed and stored on a shelf, buy commercial vinegar. This is not excessive caution. It is the one place where the difference between 4 percent and 5 percent is the difference between a preserved food and a growth medium.
Common mistakes
- Sealing the jar. The single most common failure. No air, no vinegar.
- Skipping the sugar because the apples are already sweet. Scraps carry very little fermentable sugar; the added sugar is what sets your final strength.
- Chlorinated tap water. Stalls stage one before it starts. Filter it or leave it out overnight.
- A narrow vessel. A tall bottle has a fraction of the surface of a wide jar and can take twice as long.
- Metal contact. Acetic acid reacts with most metals. Glass or ceramic only, and a plastic or wooden stirrer.
- Giving up at week three. Stage two is genuinely slow and shows almost no visible activity. Taste before you judge.
Where it goes from here
Once you have a mother, subsequent batches are much faster: pitch it into fresh cider or sugar water and skip most of the uncertainty of stage one. The same technique works for wine vinegar (start from wine, skip stage one entirely), and for rescuing any ferment that has gone too sour to enjoy on its own terms.
If your kombucha has gone sharp enough to make you wince, you are already partway through this process. Strain it, give it air and time, and it finishes as vinegar rather than as a mistake.
Frequently asked
Can I use my homemade vinegar for canning or pickling?
No. Water-bath canning recipes are built around commercial vinegar standardized to 5 percent acetic acid, and that number is what makes the recipe safe. Homemade cider vinegar typically lands somewhere between 3 and 5 percent, varies batch to batch, and cannot be verified without titration. Use it for dressings, drinks, marinades, braises, and refrigerator pickles that you eat within a few weeks. Buy commercial vinegar for anything shelf-stable.
How is this different from every other ferment on the site?
Oxygen. Sauerkraut, kimchi, hot sauce, and honey garlic are anaerobic: the whole craft is keeping the food under the brine and the air out. Acetic fermentation is the reverse: Acetobacter needs oxygen to convert alcohol into acetic acid, so the jar stays wide, shallow, and covered only with cloth. If you seal a vinegar ferment it stalls as alcohol and never becomes vinegar.
What is the mother, and do I need one to start?
The mother is a cellulose raft produced by the Acetobacter colony, the vinegar equivalent of a kombucha SCOBY. You do not need one to start, because the bacteria arrive on the fruit and from the air. A mother will form on its own, usually during the second stage, as a pale gelatinous film. Once you have one, it will speed up every subsequent batch.
There is a white film on top. Is that the mother or is it mold?
A forming mother is smooth, pale, translucent-to-cream, and sits flat on the surface like a skin. Kahm yeast is a wrinkled, dull white film that sits flat but looks crinkled. Mold is fuzzy and raised, and it comes in colors: green, black, blue, pink. Fuzzy or colored means discard the batch. See [kahm yeast vs mold](/guides/kahm-yeast-vs-mold/) for the full visual diagnosis.
How do I know when it is done?
Taste and smell first: it should smell sharply of vinegar rather than of cider or nail polish, and taste cleanly sour with no alcoholic heat. Then measure. pH strips should read around 2.5 to 3.5. If it still tastes winey, it needs more time and more air. If it tastes thin and watery, the alcohol stage never produced enough to convert.
My ferment smells like nail polish remover. What went wrong?
Acetone or solvent smells usually mean the ferment is too warm, or that ethyl acetate has built up during a slow conversion. It often mellows if you give it more time and better airflow. If it persists past a few weeks, the batch is unpleasant rather than unsafe; compost it and start cooler.
Do I have to stir it every day?
During stage one, yes. Daily stirring pushes floating scraps back under and introduces oxygen for the yeast. This is also the stage where mold takes hold if fruit sits dry on top. During stage two, once the solids are strained out, leave it alone; disturbing a forming mother just sinks it, and a sunken mother is harmless but has to start over.
How long does finished vinegar keep?
Indefinitely, at room temperature, in a closed bottle. Vinegar is self-preserving. It may throw sediment or grow a new mother in the bottle; both are harmless. Strain if it bothers you. The flavor continues to round out over the first several months.