You open a bottle of wine, pour a glass, take a sniff — and something is off. Or is it? Maybe it's damp cardboard, maybe it's sulphur matches, maybe it's something that smells disconcertingly like a barnyard. Before you pour the whole thing down the sink, it's worth knowing that the world of wine aromas is far more nuanced than "good" and "bad." Sometimes what seems like a fault is actually a feature. And sometimes it really is a fault. Here's how to tell the difference.
First: Wine Is a Living Thing
Wine is not a static product. It changes in the barrel, in the bottle, in your glass, even depending on who's tasting it and what they ate before. Because wine is alive in this sense, it's susceptible to various conditions, microbes, and transformations — some desirable, some not. The key is learning to distinguish between a defect that makes a wine unpleasant or unfit to drink, and a quality that, in the right context, becomes part of a wine's character and charm.
In recent years, with the rise of natural wine, our collective understanding of acceptable aromas has broadened considerably. The rules of the game are changing, new cultures of wine perception are emerging. Wine can be different — and sometimes stranger than we expect.
Cork Taint (TCA): Always a Fault. No Exceptions.
Let's start with the one true villain: cork taint.
What it is: Cork taint is caused by 2,4,6-trichloroanisole — TCA — a molecule with an almost impossibly low detection threshold of just 4 nanograms per litre. It forms when mould fungi in cork interact with chlorine-containing substances (from pesticides or cork bleaching during production). In 2006, the global wine industry lost an estimated 600 million bottles — 8% of all wine produced worldwide — to TCA contamination. That number has dropped significantly since, but the problem hasn't disappeared.
How to identify it: The classic sign is the smell of wet cardboard, damp basement, mould, or rotting wood. Smell the cork first, then the wine itself. Both should confirm the presence of the fault. TCA also suppresses fruit aromas, so even if the mouldy smell isn't overwhelming, an unusually flat, muted wine with no fruit expression can be a sign of cork taint.
What to do: There is no cure. If your wine is corked, return it — whether to a restaurant or a shop. Consumer protection law is on your side. And you don't need a receipt; witnesses to the purchase are sufficient in most cases. A good shop or restaurant will swap it without argument. Open another bottle.
One caveat: TCA can occasionally appear in wines with screw caps or in wines aged in barrels that were exposed to pesticides. It's rare, but if a wine smells wrong even without a cork, this is worth considering.
Reduction: The Ghost in the Bottle
Reduction is where things start to get interesting.
What it is: Reduction occurs when wine develops in conditions of limited oxygen exposure, leading to the formation of volatile sulphur compounds — mercaptans and other sulphur-related molecules.
How to identify it: Reductive aromas range from mild notes of wet wool or struck matches (a "lighter flint" quality) to, in more severe cases, rotten eggs or garlic. In some wines, these aromas dissipate quickly with aeration.
When it's a fault: If reductive notes dominate everything else and persist after the wine has had time to breathe, the reduction is too strong. It makes the wine unpleasant and closes off the fruit.
When it's a feature: This is where it gets genuinely beautiful. Domaine Roulot, Coche-Dury — some of the most celebrated white wines in the world carry a reductive signature as an integral part of their style. A light hint of reduction, what some call "the ghost of reduction," adds complexity and depth, particularly in wines from volcanic terroirs, where pronounced mineral and sulphurous notes are considered desirable and characteristic.
The key principle: "If reductive notes dominate over all components, it's probably too much, but in small amounts, they make the wine interesting." The beauty in wine is always a blend of many properties — it's an aesthetic evaluation of the whole, not a checklist of individual components.
What to do: Open the bottle and give it time. A patient decantation and aeration can transform a reduced wine. One old trick: drop a clean copper coin into the decanter. Copper reacts with and neutralises sulphur compounds. (It sounds absurd. It works.)
Oxidation: Context Is Everything
What it is: Oxidation occurs when wine is excessively exposed to air, causing chemical changes that alter its colour, aroma, and taste.
How to identify it: Oxidised wine typically develops a darker colour (orange-brown in whites, brick-red in reds) and aromas of wilted fruits, dried nuts, or sherry. The taste can be flat or "tired." If you've left a glass of wine out overnight and smelled it the next morning, you've experienced oxidation.
When it's a fault: In a young wine that should be bright and fresh, early oxidation is a problem. If your Sauvignon Blanc smells like a dusty raisin after being opened for a day, something has gone wrong in the cellar or the bottle's closure has failed.
When it's a feature: Calling oxidation a universal defect would mean dismissing entire wine categories that have shaped European culture for centuries. Fino sherry, manzanilla, the yellow wines (vin jaune) of the Jura, Madeira — these wines are intentionally made in an oxidative style, and it is precisely that character that makes them extraordinary. Many skin-contact (orange) wines also carry oxidative notes as part of their profile.
As one wine critic puts it: "If oxidation in a wine were a defect, it would not have the ability to evolve and become more interesting over decades." The oxidative aroma is part of the charm of old wines. Calling it a disease in those contexts negates entire regions of the wine world.
Brettanomyces (Brett): The Polarising One
What it is: Brettanomyces is a wild yeast strain that can colonise wine, typically due to insufficient sanitation in the winery. It produces a distinctive suite of aromatic compounds.
How to identify it: Brett aromas are diverse and can include barnyard, horse sweat, smoked meat, leather, and medicinal or apothecary herb notes. They range from subtle — adding a rustic, earthy layer — to overwhelming.
When it's a fault: At high levels, brett can make a wine genuinely undrinkable, masking all fruit and turning the wine into something that smells like a stable floor. Combating brett requires strict attention to cellar hygiene and fermentation management.
When it's a feature: In small amounts, brett adds uniqueness and character that some wines — and many drinkers — love. Certain traditional red wines from Bordeaux and the Rhône have historically carried a brett signature that was considered acceptable, even desirable, adding complexity and earthiness. Many natural wine drinkers appreciate brett as part of a wine's rusticity and distinctiveness.
The complication with brett, more than any other wine "fault," is that taste is a subjective construct. An extract from an interview with a prominent wine critic sums it up neatly: he visited Georgia and tasted a skin-contact Rkatsiteli with a winemaker from New Zealand who had never encountered the style. The New Zealander asked, "What's this bitterness?" — an unfamiliar style he had no past experience in assessing. What's a fault to one palate is character to another.
Volatile Acidity (VA): The Line Between Edge and Vinegar
What it is: Volatile acids — primarily acetic acid — form in wine as a result of bacterial activity, particularly under aerobic conditions. Acetic acid is essentially vinegar.
How to identify it: At high levels, VA manifests as aromas of wine vinegar or nail polish remover (the latter is ethyl acetate, a related compound), and can cause a burning sensation in the nose. At lower levels, it presents as a bright, sharp, almost prickly edge on the nose.
When it's a fault: If the level of volatile acids is too high, the wine becomes unfit for consumption — it simply tastes like vinegar.
When it's a feature: In small amounts, volatile acidity can act as a structural element, preserving freshness and adding energy to a wine. Some grape varieties, like Nebbiolo and Lambrusco, naturally carry higher VA levels that are considered desirable in their respective wine styles, adding unique character and enhancing acidity without tipping into unpleasant sourness.
Natural wines often carry slightly higher VA than conventional wines (since no VA-suppressing interventions are made in the cellar), and for many drinkers, that prickle of volatile acid is part of what makes them feel alive.
Unconventional Aromas: The Bigger Picture
Beyond the named faults, wine carries a universe of aromas that can confuse, surprise, or delight — depending on your experience and expectations.
The petrol/kerosene aroma is characteristic of aged, high-quality German Rieslings and is a mark of distinction, not a flaw. The smell of fresh blood or meat is characteristic of many bright Italian varieties — Sangiovese, Piedirosso — and signals authenticity. The leather saddle aroma is common in Languedoc reds, warm-climate Syrah, and ripe Carignan. Cat's pee (pipping-de-chat in playful French) is characteristic of the first nose of quality Sauvignon Blanc.
A common confusion with wine "problems" is simply lack of familiarity — with a specific appellation, a specific producer, a specific vintage. People expect an aged Burgundy to retain its fruit, and when it develops a sage tincture with age, they assume something has gone wrong. It hasn't.
The bottom line: wine perception is a subjective construct. Knowledge and tasting experience are what separate effects from defects. The more you taste, the more precisely you can place any given aroma in its context — and the more you'll find yourself delighted by things that would once have worried you.
At MUR, we open more than 15 wines by the glass every day, spanning a wide range of styles and levels of unconventionality. Our team is happy to walk you through anything strange — or wonderful — in your glass.
