There are few things in this world worse than opening a bad bottle of wine. It’s the adult equivalent of dropping your ice cream cone, or losing your sparkly balloon. What’s worse, wine faults aren’t always easy to detect, or possible to remedy even with a bar cart full of mixers or a case of Coca-Cola.

In some cases, wine is spoiled long before it reaches you, or even leaves the winery. Read on for the five most common ways wine can go bad before it’s even in a bottle.


Oxygen is wine’s ultimate frenemy. While microscopic amounts give it the comlex, funky flavors we love like vanilla, smoke, and dried fruit, a fraction more turns it to sour, brown juice. Like an apple that starts turning brown as soon as it’s sliced, oxygen starts interacting with wine from the moment grapes are crushed, tainting its flavors, aromas, and color.

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The giveaway for an oxidized wine is color. Vibrant red hues or bright, nearly clear whites are safe, but a brown tinge means air got the better of your bottle. On the palate, oxidized wines are nutty and sour, with fruit flavors taking a back seat to stale notes of underripe or dried fruit.

Microbial Growth

Microbial growth is as creepy in wine as it is at the doctor’s office. Sugar and yeast are magnets for a myriad of bacteria that eat sugar, but produce strange smells and bizarre flavors instead of alcohol and glorious wine. Brettanomyces, lactobacillus, and acetobacter are three common bacteria in winemaking that fundamentally change how a wine tastes, smells, and ages.

Small amounts of brettanomyces, brett for short, add earthy aromas and character to a wine. Lactobacillus, the same bacteria that gives yogurt and sourdough bread their distinctive tangy flavors, makes wine taste creamy in small doses and moldy in large ones, making these bacteria a constant concern for winemakers.

Bad microbes are the most common problem in winery cellars, but they’re also the problem with the most quick fixes. Because microbes live on sugar, winemakers can combat them by eliminating sugar with fermentation food, like strong yeast, and stop the problem before it ruins an entire lot of wine. Reverse osmosis machines, which are as fancy as they sound, can also remove spoilage from bacteria by rapidly spinning the wine in a centrifuge, but the practice also dramatically changes the taste of the wine, making RO a last resort for most winemakers.

If you have a wine with a lot of earthy funk on the nose or a hint of nail polish, that’s bacterial spoilage. A little bit is O.K., but when in doubt, dump what tastes bad.

Stuck Fermentations

“Stuck” fermentations are winery speak for lots that never completely go dry, or don’t form a wine where all the grape sugar has been converted into alcohol.

That’s fine for winemakers intentionally producing sweet wines, but those sugars in other wines often lead to flaw No. 2, since sugar is food for all manner of undesirable bacteria. Left unchecked, they’ll either spoil the wine or yield a wine that’s significantly different from what was intended.

Imagine if your bold, blackberry-scented Yellow Tail Shiraz or Matua Sauvignon Blanc from New Zealand suddenly smelled like a horse barn or sauerkraut? Most customers wouldn’t buy that again, making slow or stuck fermentation a huge risk for large brands.

Strong yeast strains exist to jump-start slow or stuck fermentations, but their use requires winemakers to be clued in and attentively monitor their wines so the yeast can be added before the bacteria have their way with otherwise deliciously pure wine.

Smoke Taint

The wildfires that rage across the West every year do more than destroy forests and homes; they literally destroy grapes even when the flames don’t scorch the vineyard. Because forest fires are so huge, the smoke they create doesn’t dissipate the way smoke from backyard bonfires does, which puts vineyards at risk.

Smoke from forest fires often lingers for weeks in the valleys that characterize many wine regions, eventually soaking into grape skins and tainting fruit flavors. Because grape skins are porous, they slowly absorb off-aromas and flavors from smoke, which gives the resulting wines a musty flavor and aroma, and not in a good way.

Occasionally, the fruit can be saved by making a rosé wine instead of a red, since most of the taint is caught in the grape skins, but often the fire literally causes all to be lost.

Material Other Than Grapes

Called “MOG” for short, material other than grapes includes bugs, leaves, sticks, and even birds that occasionally end up in fermenting vats of wine.

While wineries always try to avoid MOG in their fermentations, it’s nearly impossible to avoid a spider or two landing in a vat of wine. You’ll never have a bug in your bottle (thank modern filtration systems for that) but bits of debris can change wine long before the filtering process begins.

Just a few ladybugs, for instance, can taint thousands of gallons of wine. The fermentation process, with its bubbles and chemical reactions, pulls flavors and color from grapes, grape seeds, and anything else that’s mixed in, including ladybugs, sticks, and leaves, often leaving wines with a strange green flavor, reminiscent of underripe fruit or with bitter undertones.

Sometimes, it’s not your palate — it’s the wine that’s bad!