Why Does My Wine Taste Sour? Acidity, Vinegar and More

If your wine tastes sour, the cause is usually one of two very different things. Often it is normal acidity: the crisp, mouthwatering tartness that most wines are meant to have. If the wine also smells like vinegar, it has most likely been spoiled by acetic acid bacteria, nearly always because air got to it. This guide explains how to tell which one you have, what an opened-too-long bottle does, why homemade wine turns sour and how to stop it happening again.

Quick check: what is making your wine sour?

What you notice	Most likely cause	What to do
Tart and crisp, but it smells fresh and fruity	Normal acidity	Nothing is wrong. Try it with food.
Smells like vinegar, tastes sharp and sour	Volatile acidity (acetic acid)	It won’t recover. Pour it away.
Smells like nail polish remover	Ethyl acetate, often found with high volatile acidity	Same as above.
Flat, nutty, sherry-like, color turning brown	Oxidation	Drinkable but dull. Finish bottles sooner next time.
Bottle has been open for days	Oxidation, then vinegar	Recork and refrigerate leftovers.
Homemade wine, sharp from day one, no vinegar smell	Too much acid in the recipe	Measure acidity and adjust the next batch.

Normal acidity: when sour is part of the wine

All wine is acidic. Virginia Cooperative Extension explains that acids give wines their “crisp, slightly tart taste” and help fermentation along. Get the balance wrong and the wine suffers either way: with too much acid it tastes sharp, sour or bitter, and with too little it tastes flat. Winemakers who need to add acid use blends of tartaric, malic and citric acid.

So a sour impression on its own isn’t a fault. If the wine smells clean and fruity, it is doing what it was made to do. In our view, a tart white or a fresh, light red almost always shows better with a meal than on its own, which is the idea behind pairing acidic wines with rich or salty food in our wine and food pairing guide.

Tip: Smell before you judge. We’d give a tart wine a second chance with a bite of cheese or bread and olive oil. If it smells clean and fruity rather than like vinegar or nail polish, it is simply a high-acid wine.

Volatile acidity: when sour means vinegar

Volatile acidity (VA) is the winemaker’s term for the acids in wine that can evaporate, and it is the fault behind most genuinely sour, vinegary wine. Penn State Extension explains that the main one is acetic acid, the acid that gives vinegar its smell and taste. The AWRI puts acetic acid at more than 93% of a wine’s volatile acidity.

High VA often comes with a second compound, ethyl acetate, which smells like nail polish or nail polish remover. Penn State notes that acetic acid is hard to smell until VA is already a serious problem, so a whiff of nail polish is a useful early warning.

What causes it

The main culprits are acetic acid bacteria, such as Acetobacter. The AWRI explains that they turn alcohol into acetic acid when oxygen is present, which is why spoilage of this kind happens when wine is exposed to air. Penn State links high VA to too much oxygen and poor sulfur dioxide (sulfite) management, and lists the riskier situations:

• stuck or sluggish fermentations,
• natural or “native” fermentations,
• barrel aging,
• long contact with air in a part-empty container (headspace),
• bottling without enough sulfite or without sterile filtration.

US rules cap VA in finished wine. Penn State cites the federal limits as 1.4 grams per liter for red wine and 1.2 grams per liter for white wine, calculated as acetic acid.

Oxidation: flat, nutty and brownish

Oxidation is what happens when wine takes up too much oxygen. Wine Spectator’s Dr. Vinny explains that the wine’s ethanol starts breaking down into compounds such as acetaldehyde, the fresh flavors flatten, and nutty, sherry-like notes take over. The color can drift toward brown and brick tones.

The AWRI describes oxidized wine as dull at first, then cardboard-, straw- or hay-like, and sherry-like in advanced cases. Acetaldehyde itself smells of over-ripe, bruised apples. Delicate, aromatic whites such as Riesling are especially prone, while reds cope better because their phenolic compounds act as antioxidants.

Oxidation on its own makes wine taste flat and stale rather than sharply sour. The vinegar comes from bacteria, and as the AWRI explains, they need air too.

A bottle that has been open too long

This is the most common reason a wine tastes sour at home. Dr. Vinny notes that wine left in a glass overnight, or a bottle that has been open for about a week, can oxidize, and the changes take hours to days to show. Sweet, high-acid and tannic wines hold up better, but all wines suffer from too much oxygen in the end. And because acetic acid bacteria also need oxygen, a bottle left open long enough can start to smell of vinegar.

To slow it down, put the cork or cap back in, keep the bottle in the fridge and finish it within a few days. In our view, a bottle that has sat open on the counter for a week is rarely worth pouring. Our guide to how long wine lasts after opening gives the typical window for each style. A faulty closure can also let air into a sealed bottle, according to Dr. Vinny, so an occasional unopened bottle can be oxidized too.

Why homemade wine turns sour

Homemade wine turns sour for the same reasons commercial wine does, but home winemakers rarely have a lab to catch problems early, and there are plenty of chances for air to get in. The usual causes are:

• Oxygen after fermentation. Virginia Cooperative Extension calls oxygen “an enemy of wine” once active fermentation is over. Air space in a half-full carboy is the classic problem.
• Poor sanitation. Bacteria and fungi on fruit, counters, tools or in the air can spoil the wine, so the extension guide says all equipment must be sanitized.
• Not enough sulfite. Sulfites protect against bacteria and mold and help prevent oxidation. The Campden tablet added at the start breaks down over time and has to be replenished.
• Damaged or moldy fruit. Oregon State University Extension notes that acetic acid bacteria survive fermentation and need controlling afterward, and recommends more sulfite at crushing when fruit is damaged.
• Too much acid in the recipe. If the wine is sharp from the start but has no vinegar smell, the problem may simply be the acid balance. Virginia Cooperative Extension notes that every batch of fruit carries different amounts of acid.

How to prevent it

Virginia Cooperative Extension’s home winemaking guide is a good checklist:

1. Sanitize everything that touches the wine, for example with a potassium metabisulfite (Campden) solution or a winemaking sanitizer. The guide advises against chlorine bleach, which can leave an unpleasant taste.
2. Keep the airlock filled. It lets carbon dioxide out and keeps oxygen from getting in.
3. Keep air space to a minimum. Top up with a compatible wine or water, add sterilized marbles, or move the wine to a smaller container.
4. Rack carefully. Keep the end of the siphon tube below the surface of the wine in the receiving container so it picks up less air.
5. Replenish sulfite. The guide adds one crushed Campden tablet at every other racking, and suggests a free sulfur dioxide test kit to avoid using too much or too little.
6. Store it cool and dark, at about 50 to 60°F, and keep corked bottles on their sides so the cork stays swollen.
7. Check acidity before fermenting with a titration kit or pH strips, and start from a proven recipe.

Note: Penn State Extension says volatile acidity is much easier to prevent than to remediate. The fixes wineries use, such as reverse osmosis and blending with a clean wine, need lab analysis and equipment, so for home winemakers, prevention is the realistic cure.

Is sour or vinegary wine safe to drink?

As far as the sources go, it isn’t harmful, just unpleasant. The AWRI states that the compounds behind volatile acidity “represent no threat to health”, and Dr. Vinny says an oxidized wine won’t make you sick. If you have a health concern, ask a doctor.

Important: Sourness is not the only warning sign. Virginia Cooperative Extension tells home winemakers to watch for corks pushing out and for carbonation or sediment in bottled wine, signs that fermentation has restarted in the bottle. A still wine that turns fizzy and smells sour is spoiling. Pour away any wine with visible mold or an odd smell you can’t explain.

When to pour it away

• It smells clearly of vinegar or nail polish remover.
• It has turned brown and tastes flat and sherry-like when it shouldn’t.
• A still wine has become fizzy, or the cork has pushed out on its own.
• You can see mold on the surface or around the cork.

We’d rather open a fresh bottle than spend an evening with a vinegary one. Our best cheap wine picks are a good place to find a replacement, and you’ll find more guides to storage, serving and faults in Wine Basics.