Is Something Wrong With My Wine? (Part 2)

Wine faults are rarely the neat, binary failures people imagine. Most live on spectrums where chemistry, perception, and personal tolerance collide, and where a flaw can be either a minor quirk or a complete catastrophe depending entirely on dose and context. That was the uncomfortable lesson of Part 1, where cork taint, oxidation, reduction, and volatile acidity proved far more ambiguous than their reputations suggest.

Part 2 steps deeper into that ambiguity. Some faults aren’t chemical at all but biological — living organisms that evolve inside the bottle and divide tasters down ideological lines. Others hide completely until after you swallow, or strike from outside the bottle through heat, light, or simple logistical misfortune. The challenge isn’t merely recognising a fault but understanding where nuance ends and genuine failure begins.

Band-Aids, Barnyards and Savoury Leather

If volatile acidity is a cultural schism, Brettanomyces—usually nicknamed "Brett"—is an ideological warzone. Brett is a resilient, slow-growing wild spoilage yeast that hitches a ride on grape skins and loves to take up permanent residence in the microscopic pores of winery oak barrels and wooden cellar structures. Once it establishes a foothold in a winery, it’s notoriously difficult to eradicate, lying in wait to feast on the residual sugars and complex acids left behind after primary fermentation is complete.

Brett splits the wine world cleanly in two because of the highly unique, distinct volatile phenols it produces as it consumes the wine. Unlike other faults that simply ruin a bottle with a single uniform smell, Brett operates on a chemical spectrum driven primarily by two distinct compounds: 4-ethylphenol (4-EP) and 4-ethylguaiacol (4-EG).

When Brett runs rampant and produces a high ratio of 4-EP, the wine enters aggressively unpleasant territory. It smells intensely medical and synthetic—evoking antiseptic ointment or a sweaty, unwashed horse blanket. Cross into these high thresholds, and the yeast may blindfold the grape variety, wiping out any sense of place or fruit and leaving the palate tasting bitter, metallic, and dried out.

Personally, I am hyper-sensitive to Brett in its 4-EP form. Even at relatively low thresholds it immediately manifests on my tongue as the thoroughly unpleasant sensation of sucking on a plastic sticking plaster. I have sometimes been branded a "Brett-Nazi" by fellow drinkers. In fact, I was once invited to a legendary tasting of Châteauneuf-du-Pape by the esteemed New Zealand wine judge and critic Geoff Kelly, specifically to act as the table's official "Brett barometer."

My experience at such tastings highlights the massive divide in perception. Change the chemical dial to a lower concentration where 4-EG is allowed to speak, and the narrative transforms entirely. At small doses, 4-EG introduces deeply complex, rustic, and, to many, alluring notes of savoury leather, gamey smoked meats, and earthy forest floor. The ultimate example of a flaw disguised as terroir!

For many modern winemakers—particularly in the New World—Brett is treated as a severe biohazard. Detection in the laboratory can trigger urgent cellar lockdown, sterile filtration and intense sulphur dioxide additions to sanitise the wine. In their determination, Brett is a technical failure that obscures the pure varietal expression of the fruit. I’m inclined in this direction, and I’ll explain why after the next paragraph.

Conversely, in many traditional European cellars, a subtle splash of Brett is fiercely defended as an essential component of the wine's historic identity. To lovers of these traditional styles, that rustic, leathery, and slightly wild barnyard complexity is exactly what prevents a wine from tasting boring, industrial, and overly polished. It’s a tightrope walk where a master winemaker allows just enough wild yeast activity to give the wine soul, without stepping off the edge.

But if a bottle has just a little bit of Brett, there is no guarantee it will stop there. If a wine is bottled with viable Brett cells and insufficient free Sulphur dioxide to keep them asleep, the yeast will continue to slowly feast inside the bottle for years. That tiny touch of savoury leather you enjoyed upon release can evolve into a monster that has consumed the fruit and left your prized bottle tasting of nothing but drying Band-Aids. When it comes to cellaring, a little bit of Brett is rarely a stable artistic choice; it’s a ticking biological time bomb.

The Mouse in the Mouth and the Sommelier Standoff

Mousiness is the ultimate phantom of the wine cellar. It is arguably the most insidious and deeply unpleasant fault in the entire beverage world. On a chemical level, mousiness is caused by volatile organic compounds called tetrahydropyridines produced when specific lactic acid bacteria or spoilage yeasts interact with amino acids in the wine.

Mousiness is uniquely terrifying to a wine drinker because you can’t smell it in the glass. The compounds responsible for mousiness are completely non-volatile at the naturally low, acidic pH of wine. The trap springs only after you take a sip.

When the moderately acidic wine hits your tongue, your neutral-pH saliva mixes with the liquid, raises the wine’s pH level inside your mouth and causes tetrahydropyridines to vaporise. Within three to five seconds after swallowing, a nasty wave of flavour rushes up the back of your throat via retro-nasal perception. The taste is unmistakable, bizarre, and thoroughly repulsive: the pungent, stale smell of a neglected mouse cage.

Historically, mousiness was a rare defect. However, it has experienced a resurgence in recent years due to the growing popularity of low-intervention and natural wines. Because natural winemakers actively reject the use of sulphur dioxide (SO₂)—the primary preservative used to suppress spoilage bacteria—their fermentations are vulnerable to these mousy bacterial populations.

To make matters worse roughly 30% of the human population are genetically unable to perceive mousiness. Because human saliva varies slightly in its exact pH and enzyme composition, nearly one-third of the world can drink a heavily mousy wine, swallow it, and notice absolutely nothing wrong.

The Table Diagnostic: The Water Test

Because mousiness is so elusive and delayed, it can easily make you second-guess your own perception. If you take a sip and suspect a faint, creeping rodent-cage finish but aren't entirely sure, you can use a quick glass of plain tap water to confirm your diagnosis.

Take a sip of the suspect wine, swallow it, and then immediately follow it with a gulp of water. By washing the acidic wine away, the water accentuates the shift back to neutrality in your mouth's pH, heavily amplifying the hidden flaw. If that brief splash of water transforms a faint suspicion into a loud, undeniable burst of mouse cage, your palatal instincts were 100% correct. You have a mousy bottle.

The Restaurant Dilemma

Now that you are entirely sure the bottle is flawed, you call the sommelier over and explain the issue. She politely takes a small glass, sniffs it, takes a quick sip, and looks back at you with a blank, confident smile: "It smells and tastes okay to me, sir."

To her brain, that wine genuinely tastes fine. She simply belongs to that lucky 30% of the population who are genetically immune to the nasty taste of mousiness entirely.

If you ever find yourself in this awkward situation, you can use pure science to defuse the tension without insulting their palate:

• Name the Effect, Not the Molecule: Don’t just say the wine tastes bad. Instead, focus on the delayed reaction. You can say: “I am getting a heavy wave of mousiness right on the finish. The nose is completely clean, but the flaw is activating a few seconds after I swallow.” This signals to the sommelier that you understand how this specific, hidden fault operates.
• Invoke the 30% Rule: Remind them gently of human biology: “I know about a third of the population can’t perceive mousy compounds because of saliva variations. Could we get a second opinion from another staff member?” This transforms the argument from a personal clash of palates into an objective scientific inquiry. Once a second staff member tastes it, chances are high they will belong to the 70% who can taste it and will back you up.

Evil Lighting and Hot Car Boots

So far we have discussed faults born directly inside the bottle during winemaking or closure failures. But there is a final category of wine damage where the bottle leaves the winery in immaculate condition, only to be ruined by the elements on its journey to your glass. This is environmental damage, driven by two primary forces: heat and light strike.

Heat Exposure ("Cooked" Wine)

When a wine bottle is exposed to elevated temperatures—whether trapped in the hot boot of a car during a summer road trip, left under harsh retail display lights, or stored in a poorly insulated warehouse—the heat accelerates destructive chemical reactions that cook the wine and oxidise its sugars and alcohols, called maderisation.

This is done intentionally to create some of the world's longest-lived, legendary fortified styles—from the indestructible, nutty wines of Madeira itself to the glorious, unctuously sweet, and world-class Rutherglen Muscats of Australia. In those fortified styles, the heat-driven caramelisation results in exquisite layers of toffee, cold tea, and dark raisins.

However, when maderisation happens accidentally to a dry, delicate table wine, it kills off fresh, vibrant primary fruit notes, replacing them with a heavy, flat character of over-stewed, jammy, or baked fruit (like over-boiled tea or canned prunes). Structurally, the wine unravels; the refreshing acidity collapses, making the alcohol taste aggressively hot, harsh, and completely out of balance on the finish.

The heat also causes the liquid inside the bottle to expand, physically pushing against the cork. As the bottle cools down, it creates a vacuum that sucks in a heavy breath of surrounding air. This introduces rapid, catastrophic oxidation, turning white wines a deep brown-copper and red wines a dull, brick-red.

While we often think of "cooked" wine as a consumer mistake, it can also happen on a grand, tragic commercial scale during logistical breakdowns.

Recently, some years after the high-profile financial failure of Ormond in Gisborne, a massive release of the 2011 Ormond Vinoptima Gewürztraminer hit the New Zealand market at a heavily discounted price. When buyers opened these 750ml bottles, they found the wine was uniformly a deep amber-gold in colour, tasting heavily maderised. Yet, curiously, the natural corks were all entirely sound. Because this was a late vintage style with high sugar, the overall effect was not at all unpleasant, just, unexpected.

I had previously tasted that exact 2011 vintage, but from a different bottling - of Magnums intended for the Chinese market. Those Magnums were spectacular—fresh, varietal, and perfectly aligned with the pristine, age-worthy Vinoptima norm. How did an entire batch of standard bottles end up uniformly baked while the Magnums had survived?

There was a direct conflict between marketing narrative and the physical reality. The official explanation was that the wine had spent its entire life resting safely in a bonded storage facility, and the deep amber colour and baked, honeyed profile was purely due to fifteen years of intentional, late-harvest bottle age. I’m sceptical.  My theory is that this batch of 2011 bottles languished in a standard, uninsulated commercial warehouse while the receivership dragged out. A few hot New Zealand summers trapped inside a tin-shed industrial warehouse would act as a ruthless thermal catalyst, effectively baking the wine from the outside in while leaving the corks perfectly intact. That other (and earlier) vintages of the same wine and winemaking style are still available in fresh condition supports my theory.

Light Strike (Goût de Lumière)

The second environmental threat is light strike, a photochemical reaction that occurs when ultraviolet (UV) rays or short-wave blue light penetrate a bottle and react with a naturally occurring vitamin in wine called riboflavin. This reaction breaks down amino acids, transforming them into volatile sulphur compounds that mimic heavy reduction, wiping out fresh fruit notes and introducing foul aromas of wet wool, damp cardboard, or stagnant drain water.

Hearing that light strike can technically damage a vulnerable wine in a matter of hours sounds terrifying, but the reality is most white wines and roses in clear bottles on supermarket shelves are perfectly fine.

This is due to relative light intensity, temperature control and rapid stock turnover. Laboratory experiments that trigger rapid light strike often use brutal, unshielded UV radiation or direct, intense sunlight. Supermarkets, by contrast, use diffuse indoor lighting or modern LEDs that emit vastly lower levels of damaging UV and blue light wavelengths compared to old-school fluorescent tubes.

While traditional green glass does filter out roughly 50% of harmful light, the real shield for clear-glass bottles is rapid stock turnover. A popular brand of Marlborough Sauvignon Blanc or a crisp French rosé is wheeled out on a pallet, stacked, bought, and restocked within days. The light strike chemical chain reaction simply requires far more prolonged, continuous exposure under these mild store lights to gain traction. The real danger zone isn't a high-turnover supermarket shelf; it’s the clear-glass bottle that has been left sitting directly in a sunny shop window, or on the top shelf of a slow-moving corner store for months on end.

Fake Flaws

To wrap up our journey through the cellar's rogues' gallery, we need to look at a few things that often cause instant panic for drinkers but are actually harmless. Just as we have learned that a little bit of technical "spoilage" can add beautiful complexity, we also need to recognize when a weird-looking bottle is completely fine. If you spot any of the following three phenomena, do not return the bottle—pour a glass instead.

Wine Diamonds (Tartrate Crystals)

The most common false alarm occurs when a drinker finishes a bottle of white wine and finds what looks like a handful of crushed glass or shiny, jagged sugar crystals clinging to the bottom of the cork or resting in the last glass.

These are not glass, nor are they chemical additives; they are harmless and tasteless potassium bitartrate crystals, affectionately known in the trade as "wine diamonds." Tartaric acid is the primary, natural acid found in grapes. When a wine is subjected to cold temperatures—such as being left in a cold cellar or chilled at the back of a domestic refrigerator for a few days—the tartaric acid binds with natural potassium and drops out of the liquid solution as solid crystals. Many large commercial wineries "cold-stabilize" their wines by chilling them to freezing before bottling to force these crystals out mechanically before bottling.

Sediment

In aged red wines, or modern unfiltered red and white wines, you will frequently find a thick, dark, and fine-grained deposit at the bottom of the bottle.

As a red wine spends years in the bottle, its natural colour pigments and wood tannins slowly bind together, growing heavier and heavier until they fall out of suspension as solid matter. If a wine is bottled unfiltered—common in the natural wine movement and high-end artisanal estates—you may even get a slight, hazy cloudiness or yeast sediment left over from fermentation. It might look unappealing, but it is chemically inert. Simply stand the bottle upright for 24 hours before drinking to let the sediment settle to the bottom, and then gently pour the wine into a decanter.

The Five-Minute Fright (Initial Reduction)

As we discussed in the reduction section in part 1, an airtight closure like a screw-cap can occasionally trap volatile sulphur gases, leading to a sudden whiff of a struck match or burnt rubber the second you twist the cap off.

If a wine is simply suffering from initial opening reduction, the gas will blow off. Give the wine a vigorous swirl in the glass, or better, pour the whole bottle into a decanter or jug and give it five to ten minutes to interact with the oxygen in the room. If the smell completely evaporates and leaves behind a beautiful bouquet of fresh fruit, the wine wasn't faulty—it was just stretching its legs after a long time in the dark.

Towards confidence

Understanding wine faults isn’t about memorising chemistry or mastering a checklist; it’s about recognising how much ambiguity lives inside the glass. Most faults aren’t tidy, binary failures but shifting spectrums shaped by biology, environment, perception, and personal tolerance. A wine can carry a hint of Brett without being ruined, show a whisper of reduction that vanishes with air, or hide a bacterial flaw that only reveals itself after you swallow. And just as in Part 1, the real challenge isn’t spotting every anomaly — it’s knowing which ones matter, which ones don’t, and when a quirk becomes a genuine flaw.

Once you understand that nuance, the social panic of the restaurant taste test begins to dissolve. You’re no longer trapped in the agony‑aunt dilemma of wondering whether you’re imagining things, or fearing that speaking up will expose you as inexperienced. You know what faults can look like, how they behave, and why their detection is seldom black and white. You know that perception varies, thresholds differ, and even professionals disagree.

With that knowledge, the uncertainty that opened this two‑part guide finally has an answer: your own palate remains the ultimate detective. Trust your senses, understand the dose, and use your knowledge to confidently rule the table.