Can you please explain brettanomyces?

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Dear Dr. Vinny,

Can you please explain brettanomyces? What does it smell like, and why do you get it in some wines?

—Andrea E., Santa Barbara, Calif.

Dear Andrea,

Brettanomyces, or “brett,” as the cool kids call it, is a yeast, and since it can ruin a wine, it’s generally considered a spoilage yeast. But many wines, including some really terrific ones, have brett in small concentrations. Though brett can occur in white wines, it’s mostly an issue for red wines.

You’ll recognize brett from its barnyard, cow pie, horsey, mousy, pungent, stable, metallic or Band-Aid aromas. At lower concentrations, it can add a spicy, leathery note to a wine, and I think some people like it because it’s easy to pick out, and, well, people like to recognize flavors and aromas in their wines. People’s thresholds of perception (and tolerance) of brett vary—some don’t notice it, while others are more sensitive. It’s controversial to call it an outright flaw, but wines with brett at high concentrations all start to taste the same to me—not good. It’s not a health concern, unless you consider drinking wines that smell like cow pies as detrimental to your mental health.

How does it get into some wines? I’m going to gloss over the microbiology, but quite simply, brett can develop at practically any stage of production. The yeast can be on the grapes themselves, it can be hanging out in a winery, and it can hide in barrels. Since the winemaking process is all about fermentation and yeasts and converting one thing to another, there’s plenty of opportunity for brett to occur. Some winemakers consider a bit of brett as their house style, but for others, once brett takes residence in a cellar, it can be difficult to get rid of.

—Dr. Vinny

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