Even if you love the “barnyard” funk (previously discussed under the Taste section), there’s a point at which it gets… a little too funky.
Brettanomycesor “Brett”, for short, is a yeast strain that can become too pronounced, at which point this “farm animal” or “gym locker” kind of note overpowers the fruit, rendering the wine unbalanced. A certain amount of it is often welcome, and produces the earthiness sometimes mistaken as terroir. We see this in wines from the Rhone region as well as sometimes in those from Italy or Napa. How much or little it is accepted depends on the region. Some wWinemakers in Australia are less tolerable of it and prefer not to bottle wine with any sign of this note.
Another common flaw in natural wine is Volatile Acidity, or VA. It gives off either a balsamic vinegar, or worse—nail polish remover— taste. Sounds delicious, right? There is an actual, set gram/liter level of VA accepted in French appellation wines, but it all comes down to a taste test. Sometimes the fruit and other aromas balance the wine enough, and in other circumstances the bottle is just too “off”.
Mousiness, is another one often referred to when it comes to natural wines. Sometimes oxygen exposure can set off a bacterial infection which causes a “mousy” or sour milk kind of finish which can only be tasted, not smelled, as with VA. This may be corrected (by removing free oxygen). It doesn’t always render the wine undrinkable, but some people are more turned off by this note than others.
Oxidation can also spoil wine—natural and traditional alike. Sulfites are said to help protect certain compounds though, and therefore natural wines are slightly more susceptible to this fault. Tannins also help protect the wine against oxidation, so reds and skin contact wines have a slight advantage there. Oxidation happens when the wine is (somewhere along the way) exposed to too much oxygen and the wine matures too quickly, losing some of its vibrancy in taste and color. The wine begins to turn into vinegar, which becomes the dominant note.
A word about oxidation—it is not to be confused with the term “oxidative”. This refers to a style of winemaking that deliberately exposes the wine to some oxygen to bring out fruit and nut notes, and adds texture to the wine. Oxidative wines are in demand, an oxidized wine is a misfortune.
Apart from these common flaws which cannot be fixed, unfortunately, sometimes a natural wine can just taste a bit “off” when you first open it up. The best thing to do is to decant it and see if, with the help of a little oxygen and room to readjust outside the bottle, it re-harmonizes on its own. Give the wine 30 minutes and check in, and then another 30 minutes if it seems like it’s changing for the better. Let taste be your guide.