Brett: our love-hate relationship with this stinky yeast
Brettanomyces or “Brett”, as it is commonly known in the beer and wine world, is a yeast that gives off an earthy, savory and soil-like flavor. At low levels, it gives notes of meat, game or bacon, which can be attractive, especially for the beer folks! Hoppy, Belgian-style lambics with lots of Brett is a celebrated style. At higher amounts in wine though, it is undesirable, resulting in ‘off’ aromas of band-aid, barnyard, sweaty socks and wet leather.
What is Brett…chemically?
First identified in 1930s, this yeast can utilize a number of chemical compounds under restrictive conditions and produce a range of by-products. The four key by-products are esterases, volatile fatty acids, tetrahydropyridines and volatile phenols. The two most important phenols which Brettanomyces produces are 4-ethylphenol and 4-ethylguaiacol.
They live off residual sugar, ethanol and cellobiose (the compound found in the wood of the barrels). Hence, the preponderance of Brett is in wines that have undergone barrel aging. No wonder it is hard to get rid of this stinky yeast.
Is it a spoilage yeast?
Most winemakers consider Brett to be a spoilage yeast. The primary reason is that it is hard to contain a Brett contamination JUST to have the positive flavors that would add complexity to the wines, both white and red. Once the yeast spreads, it is very hard to control and goes on to produce off flavors.
So, has your wine gone down the drain?
No, not really…if you or your coworker at the winery has a good nose! The first step upon detection of Brett is to immediately add sufficient amount of sulfur dioxide. In addition, wines will be sensitive to Brett spoilage if there is a delay in the conversion of malic acid to lactic acid (which wine snobs call malo, i.e. malolactic conversion). Lack of hygiene (believe it nor not!) is one of the primary contributors to Brett. So, the cleaner the winery, the lower your chances of Brett contamination (microbiology 101).
However, recent advances have made it possible for the early detection and control of this yeast. Selective growth media can be used to restrain the growth of Brett. Nowadays, the commercial preparation of chitosan specifically targets Brettanomyces cells. The Brettanomyces cells are absorbed by the chitosan and settle out of the wine, ultimately resulting in cell death.
If none of these remedial efforts work, the winemaker will need to throw away the barrels, wipe down all the equipment and start fresh!
References:
- The Oxford Companion to Wine (4ed.) Edited by Jancis Robinson and Julia Harding
- Wine Tips & Tricks; Wine Folly by Madeline Puckette
- Scott Labs Fermentation Handbook
- White Labs yeast selection chart
- Images are taken from Adobe Stock, and Pixabay