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Mousiness Is Natural Wine’s Biggest Flaw


It was 2015 and I was tasting wine at a store that no longer exists, staring in puzzlement at a glass of something cloudy and orangish from Chile. It was my first time tasting natural wine’s bacterial infection du jour, a mysterious, microbial kraken lurking within countless carbonic reds in clear glass bottles with hand-drawn labels.

Unlike other flaws, such as being made of gewürztraminer (jk!) or being corked, mouse often isn’t immediately detectable. While in serious cases it can be present upon opening, it generally begins to emerge about 30 minutes after, presenting as an off taste that is variably described as “corn nuts,” “puppy’s breath” and “vomit.” Regardless of when it shows up, it most certainly ruins the wine—no one, it turns out, wants to drink côt that tastes like a hamster cage.  


The thing that has made mouse more than just your standard-issue wine flaw, though, isn’t just its pervasiveness, but its connection to natural winemaking. It has been wielded as grounds for dismissal, a way to paint natural winemakers as unclean, flawed and inconsistent, not to mention stubbornly dogmatic. But the more one investigates mouse, the clearer it becomes that the quality is more nuanced, and more transient, than originally understood. Instead of being an unfixable problem, it begins to appear more like a flaw in how the wine is understood and contextualized.


The first known reference to mouse appears in 1894 by way of J.L.W. Thudichum’s A Treatise on Wines, and is described as “a peculiar disagreeable flavor in wine … resembling the smell of a residence of mice.” Years later, in 1913, Müller-Thurgau (inventor of the German grape Müller-Thurgau) and his partner Adolf Osterwalder first noticed that about 30 percent of people can’t taste mouse, linking it to mouth pH. There’s not much before that to suggest that anyone was worried about it, not in the early 20th century or in the previous 8,000 years of wine drinking. Likely, it got lumped in with a whole host of other bacterial nasties, all of which have the same traditional solution: the application of sulfur, which the wine writer Aaron Ayscough, in his The World of Natural Wine, describes as being used (sparingly!) since the Hellenic Era.  

The more one investigates mouse, the clearer it becomes that the quality is more nuanced, and more transient, than originally understood.

French wines destined for the market around the time mouse was first discovered generally saw 10 to 12 grams of SO2 per hectoliter of juice applied via burning wick or stone, which apparently is enough that mouse never got much press. After the world wars, mouse became even more scarce, as industrial winemaking became the dominant mode of production throughout the world. At the end of the century, winemaking manuals were advocating SO2 levels of 20 to 200 grams per hectoliter, which is a true A Desert Called Peace–type scenario. This coincided with two generations of chemicals, developed for our various world wars, being pumped into the soil as fertilizers, herbicides, pesticides and fungicides.

In his manifesto, Cultural Insurrection, the sommelier, cultural critic, filmmaker and farmer Jonathan Nossiter writes that by the 1960s vineyard soils were so laden with dangerous chemicals that it became increasingly difficult for grapes to ferment natively. Thirty years later, in the late ’80s and early ’90s, in nearly every corner of the wine world, small pockets of resistance grew up in response to the environmental and human consequences of industrialization, not to mention how lifeless and uniform wine had become. The most famous resisters were the so-called “Gang of Four” (or Five, or Six, etc., depending on which wine importers you ask) in Beaujolais, who, led by the chemist Jules Chauvet, decided to cease using added chemicals, including, in some cases, SO2, in both the vineyard and the cellar. It was a radical inversion of the mid-20th century’s ethos of better living through chemistry.

Mouse quickly became part of the conversation among oenologists and early natural winemakers, eventually crossing over into the Paris mainstream along with natural wine, and then onto New York City in the early 2000s. Fast-forward about a decade, and all of a sudden the flaw was in everyone’s glass, and on everyone’s lips, as natural wines achieved critical mass.

It’s true that today we are drinking in a market awash with mousy wine. Given this modern history, it’s easy, then, to blame natural wine zealots for throwing the baby out with the bathwater, conflating dangerous chemicals, like Roundup—which frankly is something we need to speak to the Hague about—and sulfur dioxide, which is largely safe, even if you don’t want to get it in your eyes or mucous membranes. But it’s pretty hard to find those zealots; most people within the natural wine community make allowances for small doses of SO2. But, more importantly, SO2 is not quite the silver bullet it once appeared to be.

Pascaline Lepeltier, sommelier and author of Milles Vignes, reports encountering wines that had been doused with SO2 and still showed mouse. “[Since 2016] you started to see it more outside the perimeter of natural wine [and] since ’18 I’ve tasted it in more… I wouldn’t say conventional wines, but [in wines from] people who are using sulfur,” she says. This is corroborated by sommelier Amanda Smeltz, who told me that she’s tasted mouse in wines with 8 to 10 grams of SO2—which is enough to change the taste of the wine, but clearly not always enough to prevent microbial activity. 

It takes nine months to create a human, and when it comes out, it can’t walk, talk or feed itself. A bottle of natural wine needs a year to land on its feet. Some are great before [that], but in general they need time.

More confusing is the question of timing—that is, when to add a small dose of sulfur and how that might impact mouse’s ability to embed in the wine. All of this contributes to a general feeling that, when it comes to mouse, everyone’s just guessing. Many winemakers and experts agree, however, that patience, a thing we’re taught to revere in wine, can be a powerful prophylactic here, too.

According to Ayscough, waiting on wine to resolve—i.e., letting it sit somewhere nice and cool until it sorts itself out—was utilized by the original natural winemakers in Beaujolais. Lepeltier further explains that the molecule that creates the mousy taste, tetrahydropyridine (known as THP), unwinds over time and becomes “imperceptible.” This timeline is, of course, not fully known, but as Camille Rivière, a natural wine importer based in France and working in the U.S., says, “It takes nine months to create a human, and when it comes out, it can’t walk, talk or feed itself. A bottle of natural wine needs a year to land on its feet. Some are great before [that], but in general they need time.” This is a particular issue with less-affluent winemakers (including many in the natural scene), who are unable to afford holding back wine and feel pressure to sell them immediately post-bottling. Brent Mayeux, winemaker and proprietor of Stagiaire Wines in the Santa Cruz Mountains, puts it more bluntly: “Mouse is more often than not the fault of importers not waiting,” rather than a flaw with the wines themselves.

Will Ryan, ex-brewer, menswear icon and founder of the painfully cool Substack newsletter Wild Thoughts, and Pete Bloomberg, the owner and winemaker behind Llewelyn Wines, were both kind enough to explain the biochemistry behind mouse’s ability to become imperceptible over time. It largely went over my head, but crucially: THP, aka mouse, is bound up with brettanomyces, aka brett, a strain of yeast that is responsible for flavor compounds that run the gamut from incredibly delicious (horsey Rhône syrahs) to pretty gross (pét-nats that taste like Band-Aids). Brett, while often implicated as being a cause of mousy flavors, is also responsible for dissolving them, breaking down one easy-to-taste type of THP into a different, less-detectable one.

Garrett Oliver, Brooklyn Brewery brewmaster and author of The Oxford Companion to Beer, elaborated with a pithy summary, saying, “Brett, when left alone, creates many of the flavors most prized in classical wines, but when attacked … it creates ‘the funk.’ … The irony is notable.” This lines up with conversations I’ve had with winemakers from all over the wine world, in which mouse is viewed as a temporary phenomenon that is tied to moments of disturbance in the wine: racking, bottling, and, crucial for people in the United States drinking imported wine, shipping.

 The connection of mouse with disruption in winemaking and storage goes even further. Years ago, in Catalunya, a respected winemaker linked mouse in the glass with drought vintages, saying that the pH disturbances in the vineyard often resulted in wines that needed more time to resolve. Smeltz says that the vagaries of climate are more apparent in natural wines, leading to “less-stable wine because the agriculture itself is not stable… We don’t see that in industrial wine because it’s not transparent, but in natural wine you see the difficulty of climate.” In other words, natural wine’s monomania at presenting an unadulterated wine means that, over the last few decades, we’ve been tasting vineyards that are struggling to adapt to a climate that is veering off-kilter in seemingly new ways each vintage. 

Mouse at the hands of skilled winemakers can be looked at as something the wine is going through—a journey, rather than a destination.

Explaining why mouse is so prevalent in wine today doesn’t mean that I’m thrilled to encounter it, nor does it mean that it’s acceptable in a glass. But diagnosing it as a fixed flaw dismisses the nuance surrounding it, and what it can teach us about our quest for what sommelier and wine consultant Maia Fleming calls natural wine’s goal of “microbial equilibrium.” 

To be sure, there are wines made by unconfident winemakers in bad conditions that may never resolve, but there are less of those each vintage as winemakers gain skill and understanding of their terroir. More likely, mouse at the hands of skilled winemakers can be looked at as something the wine is going through—a journey, rather than a destination. I think an apt comparison is, say, incredibly abrasive tannins in nebbiolo or reduction in white Burgundy, or even just the wound-up feeling one gets in young, age-worthy wines in general—these are, oftentimes, incredibly unpleasant sensations, but not ones we dismiss out of hand as flaws.

Of course, that doesn’t really do much for the poor sap who just bought an undrinkable bottle, or the cash-strapped winemaker who cannot afford to hold their wines for another year to make sure they’re stable. As such, it becomes more and more critical for those in the natural wine space to be honest about what to expect from a bottle, even if it’s bad news. Some wines need to be drunk quickly or shared with friends who can’t taste mouse. Some wines need a year or two—patience we’re quite happy to extend to, say, a bottle of Napa cabernet or Barolo. Perhaps, then, we should extend the same grace to a new crop of wines that is just as capable of evolving.

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