Some natural wine has faults, and it has always depended on the producer. Many natural producers add little or no sulfur dioxide, or SO2, the preservative that protects wine from oxygen and spoilage microbes. That leaves their wine more exposed to a few faults, and puts more weight on how they work in the cellar. Where a fault begins is also partly a matter of taste.
Oxidation
Bruised apple, nuts and sherry
Brettanomyces
Band-Aid, horse and barnyard
Mousiness
Most often found in wine with little sulfur dioxide
Volatile acidity
Vinegar
Why wine without added sulfites is more exposed
Winemakers use SO2 against the causes of several faults. It slows oxidation and holds back Brettanomyces and the lactic acid bacteria behind mousiness. A wine made without it has less protection against all three.
The Australian Wine Research Institute saw mousy wines rise twice: in the 1990s, when winemakers moved to lower SO2 in red wine, and in the 2010s, with high-pH wines, minimal SO2 and little or no filtration in white wines. A 2023 analysis detected one of the mousy compounds in almost all the wines it tested that were made with limited SO2.
It depends on the producer
Two producers can both skip added sulfites and make very different wine, because the risk turns on cellar hygiene, the pH of the wine and its exposure to oxygen.
Many producers now add a small dose of SO2 at bottling and nothing before. Wine writer Jamie Goode described that approach as “almost mainstream” in 2019. Wine writer Simon Woolf advises a small sulfite addition at racking or bottling when free SO2 drops under 10 mg/L, to hold off mousiness.
In our experience, natural producers today put a renewed focus on releasing only wines without overwhelming faults.
Where a fault begins is partly subjective
People perceive faults very differently. In one study of mousiness, the thresholds of 23 tasters spanned more than a 1,000-fold range. The Australian Wine Research Institute says tolerance for volatile acidity varies with the style of wine and the individual.
Researchers also disagree about low levels. A 2017 study found Brettanomyces may add complexity at low concentrations. An Australian study of 104 red wine drinkers found every sample with Brett compounds was liked less. The same institute says hydrogen sulfide below its detection threshold, and ethyl acetate at low levels, can add complexity.
We think a wine with a slight fault can feel more expressive and alive than a spotless one. We draw the line at faults that overwhelm the wine.
How to tell funk from a fault
- Mousiness shows up after you swallow, as a taste of crackers or a mouse cage that lingers. Rub a drop of wine on the back of your hand and smell it to check.
- Volatile acidity smells of vinegar, and ethyl acetate of nail polish remover.
- Brettanomyces smells of Band-Aid, horse and barnyard, and mutes the fruit.
- Oxidation smells of bruised apple, nuts and sherry.
The wine faults guide covers each of these in detail, along with cork taint, reduction and heat damage.
Common questions about faults in natural wine
- Is natural wine faulty?
- Some is, and it depends on the producer. Many natural wines have little or no added sulfur dioxide, which leaves them more exposed to oxidation, Brettanomyces and mousiness. In our experience, natural producers today put a renewed focus on releasing only wines without overwhelming faults.
- Why do some natural wines taste mousy?
- Mousiness comes mostly from lactic acid bacteria, and researchers link it to wine with little sulfur dioxide, high pH and oxygen exposure. Many natural wines have little or no added sulfur dioxide.
- Can natural wine be free of faults?
- Yes. Producers lower the risk with strict cellar hygiene, and many add a small dose of sulfur dioxide at bottling.
- Is a little funk a fault?
- It depends on the taster. Sensitivity to mousiness varies more than 1,000-fold between people, and studies disagree on whether low levels of Brettanomyces add complexity or spoil a wine.
Sources
- Australian Wine Research Institute: wine flavours, faults and taints
- Kiyomichi et al. (2023): mousy compounds in wine
- Tempère et al. (2019): sensory methods for detecting mousy off-flavor
- Jamie Goode (2019): the mystery of mousiness
- Simon Woolf (2024): the complete guide to mousiness
- Schumaker et al. (2017): consumer perception of Brettanomyces
- Australian Wine Research Institute: Brettanomyces FAQ
Icons drawn from photos on Wikimedia Commons by Andy Mabbett, Sandy Horvath-Dori and Ivar Leidus (CC BY-SA 4.0 and CC BY 2.0). The mouse is from a public domain photo.
Keep reading
The wine faults guide covers all eight common faults. The sulfites guide covers the EU and US limits on sulfur dioxide.
Read the wine faults guide Read the sulfites guide Read the natural wine guide
