Often, when you think of wine faults, you think of a wine being "corked". This is one type of wine fault, but there are other faults and flaws that can give off unpleasant aromas and flavors and result in bad wine. It's helpful to know the characteristics of a few of the common wine faults, so you can tell just went wrong.
Common Wine Faults and Flaws
Wine is a living and ever-evolving drink that changes with exposure to things like UV rays, oxygen, time, and bacteria. In the winemaking process, it's super important to keep everything as clean as possible to help mitigate any unwanted bacteria from spoiling a vintage. But, there are many opportunities between fermenting, aging, bottling, storing, and traveling for things to go wrong. These wine faults and flaws are the most common.
Oxidation
It's hard to keep a wine's contact with oxygen to the minimum from its conception; however, it's crucial to help keep many of the fresh and vibrant notes. While a few wines actually are defined by their intentional exposure to oxygen, like sherry or some of the star whites from the Jura, France, most wines aren't intended to have any oxidative effects. Oxidation can and does occur in some amount during all stages of the winemaking process via aging, but great care is taken to minimize it so that only the desired effects for the particular grape and style are achieved.
What to look for: Oxidized wines look and taste as though as they've lost the bounce in their step. Just as a cut apple turns brown sitting out, the color of red and white wines will fade and turn an unpleasant brownish with exposure to oxygen.
What to smell/taste for: White wines that were once aromatic with fresh stone fruit, apple blossom, honeydew melon, or green grass take on deeper aromas of bruised fruit and nuts. But like, not in a great orange wine type of way. Oxidative red wines essentially start turning to vinegar and smell like it too.
Mouse
Mouse is an undesirable bacteria that can sneak into wine and really make your head turn, and not in a good way. It can be (but not always) more prevalent in natural wines made with zero added sulfur. It's an odd fault in that it becomes more apparent and increasingly unpleasant the longer the bottle is open.
What to look for: Mouse doesn't really provide any visual cues.
What to smell/taste for: The sensation of mouse is particularly unpleasant. Like you might guess, mouse leaves a lingering taste of an unclean rodent cage, gone-off cured meat, and dog breath. Queue squinty emoji with tongue sticking out in disgust.
You'd think this fault would be one that would make you keel over when you open the bottle, but strangely enough, mouse has more of a presence on your palate and is less noticeable to your nose alone.
Reduction
Reduction is the opposite of oxidation. So with a reductive wine, it has so little exposure to oxygen that it actually creates its own aromas and notes that can drown out a wine. When a wine is fermented and aged in an inert vessel that doesn't allow any oxygen to pass through, the wine can get a little stuffy. With this lack of oxygen, volatile sulfur compounds can develop.
What to look for: You won't notice a difference just swirling the wine in your glass with your nose plugged.
What to smell/taste for: You will, however, notice a wine's reductive aromas upon opening the bottle. A reductive wine will have a distinct sulfur characteristic. Think old cabbage, hard-boiled or rotten eggs, or a lit match. These will come through on your palate as well, tasting like burnt rubber and rotten eggs.
Brettanomyces
Ah, Brettanomyces, affectionately known as Brett. While this yeast defines certain styles of beer, it can quickly overtake a wine, and the grape characteristics can get lost in the process. Brettanomyces is an aromatic, wild yeast that is easily cultivated in the natural environment and therefore can easily make its way into the fermentation vessel in the cellar.
What to look for: Brett isn't something you'll see.
What to smell/taste for: It is something you will definitely notice when you bring the glass to your nose or/and take a sip. It has an overwhelming smell of…wild. Best described as "barnyard", it will conjure images of horse stables, manure, game meat, hay bails, and band-aid. There can also be a lingering metallic taste on the finish.
TCA (Cork Taint)
Cork taint (2,4,6-Trichloroanisole) or TCA for short, has somehow become the catch-all wine fault that even non-wine drinkers will suggest is what's off with your wine. Despite potentially being over diagnosed, it is a very real wine fault. It's from the chemical compound that arises when certain phenols interact with natural cork. The result is unpleasant and will have you pouring your wine down the sink. The good news is that you are less likely to run into this fault with screw-top wine or synthetic bottles.
What to look for: At a glance, you won't see anything different about a wine with TCA.
What to smell/taste for: The smell of TCA is undeniably bad. It smells of a damp basement, musty and wet cardboard, wet dog, and moldy shoes, leaving the wine's flavors muted and washed out.
Volatile Acidity (VA)
Volatile acidity, or VA for short, is attributed to specific strains of yeast and bacteria that can develop during the winemaking process. The yeasts and bacteria create acetic acid and can quickly turn a wine into vinegar. While lots of VA in a wine is undesirable to everyone, some people are less bothered by small amounts that may occur. A tinge of VA may give a wine a bit of sweet and sour edge. With the right varietal and style, this could translate to more complex characteristics - like taking a ripe red strawberry and giving it a touch of tangy balsamic.
What to look for: This is another invisible flaw.
What to smell/taste for: Volatile acidity is found on a spectrum and can smell and taste of a subtly sweet vinegar all the way to a harsh white vinegar you'd only dare clean with. A twinge of VA is not uncommon in some of the more new age and renegade natural wines.
Heat Damage
Wine is susceptible to hot conditions and drastic temperature swings. If a wine is exposed to particularly warm conditions, it will actually start to cook the wine, and all the fresh fruit notes will take a turn toward baked and jammy.
What to look for: You may not see that the wine has heat damage; however, if you see that the cork of the bottle has been pushed out, this could be a side effect of heat damage. In this case, the wine may have started to oxidize, and you could see oxidative symptoms such as browning in color.
What to smell/taste for: Hot wine is, well, not very pleasant to drink. But even if the wine has been brought down to the correct temperature, if it has been damaged by heat, it will retain a sweet, lush, jammy profile that smells and tastes artificial.
Do All Wine Flaws Create Bad Wine?
There are wine faults that are truly, deeply, well…faults. These faults result in undrinkable wine. Then, there are minor flaws that, depending on the palate, are unnoticeable, unappreciated, not a big issue, and everything in between. Long story short, a wine may be a bit flawed to someone and not to another.
If a wine drinker is used to a classic representation of nebbiolo from Piemonte and drinks a young vintage that opens up with an ever so subtle effervescence, they will see that as a flaw. However, if a die-hard natural wine drinker that searches out funky wines drinks the same wine, they may feel that very flaw is more of a unique expression of the grape.
Look, Smell, and Taste for Wine Faults
Upon opening your wine, give it a once over before you dive straight in. There will be more than one indicator if your wine is flawed. Narrowing in on the specifics can help you determine just what is wrong with your wine.
