Meet Brett - Tech 101

24 June 2019. Words by YGOW.

For most of us, technical detail is hardly the most compelling thing about wine. And certainly not the most romantic. And while we’re happy to keep scientific evaluation out of our glass most of the time, having a little familiarity with the nuts and bolts can be pretty useful. Knowledge is power, after all. So, want to know why your glass of shiraz tastes like a pony? Read on.

Brettanomyces has got to be one of the dirtiest words in wine – reviled by many, its existence completely ignored by others. So, what is it? (Please remember this is a general overview, so any experts on the microbiology of wine should take the dog for a walk.) Well, our friend Brett (we’re capitalising here, as it seems proper) is basically yeast (in this case a non-spore forming fungus) that is fuelled by sugars in wine, and even other substrates present in the wine or barrel, and produces volatile phenols and acids that can have, depending on the concentration, undesirable flavour implications for the wine.

Brett produces three relevant molecules: 4-ethylphenol is pretty nasty in concentration, full of unkempt barn, horse and band-aid characters; isovaleric acid is not much better, giving off rancid, sweaty and even, ahem, vomit aromas; while 4-ethylguiacol has bacon, smoke and clove notes. Now that doesn’t sound bad at all – and it’s what people who talk about ‘good Brett’ are referring to. The problem is that 4-eg is on the shy side and likes to have plenty of its stinky friends around at all times. Plus, even though it’s always lower in concentration, it is more volatile and drives the overall impression of Brett from the 4-ep and isovaleric acid. Good luck enjoying its smoked bacon pleasures!

And while Brett loves all the same food that fermentation yeasts do – glucose and fructose – it will snack away on the unfermentable sugars, too. Once the fermentation yeasts have expired, Brett will scavenge whatever sugars are left, leaving the wine with varying degrees of band-aid, horse and barnyard aromas and a palate stripped of texture, with a metallic tang. Delicious. So, one of the big issues is that it’s very slow and resilient and will keep ticking away in bottle, meaning that sometimes a wine might go to bottle looking squeaky clean, but can end up looking distinctly equine over time.

The enemies of Brett are fastidious hygiene, sulphur dioxide, low pH in the wine, low temperature and filtration. Red wines are typically more vulnerable due to their make-up (the polyphenols in the skins are precursors) and making, but whites are not immune, although its presence is much harder to identify.

Brett can be pretty virulent and can strip a wine of its fruit, mask regional character and turn that prized beauty ugly, but not everyone sees it that way. Some tasters actually like Brett in certain concentrations, and with certain varieties, but good luck controlling it if you’re a winemaker, as it doesn’t behave like other yeasts.

Learning to spot Brett can take a little time (plus the tolerance thresholds among tasters vary), but, like cork taint, once you’ve locked onto it you won’t forget it. And whether you see its presence as a fault or added character is entirely up to you. After all, your enjoyment of wine is a completely personal matter.

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