Brett: when sanitation meets wine style

Wines & Vines, Sept, 2004 by Tim Patterson

Ah, Brettanomyces (aka "Brett"), the spoilage organism that's also a flavor enhancer. Or perhaps the flavor enhancer that's also a spoilage organism. Smoke and spice, Band-Aids and saddle sweat, a little complexity or a lot of infection. Judging from the number of conferences and technical seminars devoted to this pesky fungus, it may be the wine industry's favorite wedge issue. Since the permanent eradication of Brett in most winery settings is well-nigh impossible, the battle to control the bug goes on--and so does the debate.

The hardiness of Brettanomyces and of the controversy that surrounds it were both in evidence at the recent full-day Brett symposium held in conjunction with the meetings of the American Society for Enology and Viticulture (ASEV) in San Diego in June. The ASEV session pulled together researchers from Portugal, Switzerland, Australia, Cornell, UC Davis and wine industry consulting firms for presentations on genetic and physiological diversity among Brettanomyces strains, detection and identification, control strategies and the complex sensory calculus of Brett-influenced wines. The rogue yeast symposium was a hot ticket, with the hands-on--or rather, nose- and palate-on--sections providing particularly strong stuff.

The love/hate relationship Brett inspires was obvious in the acknowledgements: Many thanks were given for research assistance and for sample wines to "wineries that shall remain nameless."

The opening speakers emphasized that Brettanomyces is ubiquitous and resourceful. It is found all over the wine world, living happily not only in barrels but in tanks, hoses and just about anything that comes in contact with water. It shows great ingenuity in locating sources of fuel (mostly sugars). It can bloom unexpectedly after periods of relative dormancy; it can persist for long periods of time in a kind of zombie state--"viable but not culturable"--and then come back to haunt.

Plus, Brettanomyces isn't an "it," it's a "them." Five species of Brettanomyces have been identified, though only one--B. bruxellensis--is a major concern in winemaking. It can exist in two modes: good old normal Brettanomyces and the sexual, spore-forming type called Dekkera. The closer researchers look, the more sub-strains they find; the major collections now hold dozens of distinct variants. Brett has a strong capacity to adapt to changing environments and morph into new strains that differ significantly in what they like to eat, what level of alcohol and pH they're comfortable with, and how well they resist sulfites.

The basics of a strategy to discourage Brett in the winery are pretty well established. Elevated pH and the presence of residual sugar (in unfiltered wine) create favorable conditions for Brett. A consistent sanitation regime and careful monitoring of free S[O.sub.2] levels are key to controlling it. Barrels should only be topped with wine known to be clean; barrels with identified Brett character should be quarantined and processed separately. (One presentation surveyed common methods for sanitizing barrels, and concluded that none of them is bullet-proof, since Brett will work its way deep into all the nooks and crannies of the wood.) Filtration and treatment with dimethyl dicarbonate (DMDC, sold as Velcorin) are available as after-the-fact remedies.

Given the mutability of the Brettanomyces clan and the possibility it won't behave the way it's expected to, regular testing in the lab and with the old-fashioned sniffer is essential. Knowing precisely what's going on is especially important for wineries whose house styles tolerate a whiff of Brett.

The Brett Aroma Wheel

Once again, that whiff of Brett isn't an it, it's a them. While most wine faults have a single, commonly accepted descriptor, Brett has a page full: plastic, medicinal, metallic, Band-Aid, rancid, cheesy, mousy, burnt and/or wet wood, animal sweat, foot odor, barnyard, stables.... (One speaker at the ASEV session added monkey excrement, which few in attendance could validate from direct experience.) On the upside, there's smoke and spice.

Brettanomyces produces several volatile compounds while it does its thing. The most common byproduct is 4-ethyl-phenol (4-EP), the presence of which is routinely used as a laboratory indication that Brett is at work. 4-EP is associated with the barnyard, Band-Aid and sweat aroma zone; 4-ethyl-guiacol (4-EG), produced in smaller quantities, comes across as smoke and spice. Isovaleric acid gets credit for the rancid and horsy elements.

These dubious compounds don't show up by themselves (except at ASEV meetings); they occur in the context of wine, mingled with fruit and oak and a host of other things. Leslie Norris of FlavorSense began by noting that small amounts of Brett can make the fruit in a wine seem heavier, while large doses can cancel it out entirely. Getting down into the details, Norris led a fascinating exercise in do-it-yourself flavor chemistry. By dipping paper swabs into bottled concoctions, participants were able to mix and match different Brett-y aromas with different wine-y aromas, producing widely divergent results. "Sweaty" Brett, for example, snuggled up to oak and made something nice and spicy, while "medicinal" Brett picked a fight with the wood. Throw in a swab of strawberry and the permutations get even more interesting.