Straight Outta Da Bunghole
Near daily discoveries in the field of wine science now elucidate once mysterious wine conundrums, from the labor-intensive detection of individual aromatic phenols to the whodunit gene sequencing that authenticated Zinfandel's origin. In fact, research now shows that very specific once tolerated, off odors in wine are actually secondary to microbiological infestation. What was once regally deemed terroir and accepted as "aromatic complexity" is now simply a yeast contamination problem. Even today wine aficionados wrestle with categorizing wines as having a "barnyard" or "sweaty saddle" aroma, since to non-wine lovers such endearing terms sound kind of gross. Of course these monikers were never intended to be pejorative but simply were considered a component of a wine's typicitie. Nowhere was this more evident than in the great French Burgundies (made from the pinot noir grape). Lusty earthiness and wet soil aside, when descriptors like "wet mouse fur, manure, medicinal, plastic, wild game, rubber boots, wet leather, and horse sweat" encroach on polite dinner conversation, perhaps it's time to find classier friends. But these adjectives are just partial list of the sometimes yummy ("bacon") and more often rancid ("tinny metallic fish taste") olfactory descriptors of Brett tainted wine. Brettanomyces/Dekkera yeast is a ubiquitous critter that colonizes wine equipment, oak barrels, hoses, and other sundry winery equipment. And once that tenacious microbe moves in, he's a hard house guest to eject. Judicious sulfide use, complete fermentation to dryness, low cellar temperatures, low pH, and limited exposure to oxygen all help curb Brett's voracious appetite for sex, multiplication, and yeast porn in your bottle. And here's what we know: Brett uses 2 unique enzymes called "CD" (cinnamate decarboxylase) and "VPR" (vinyl-phenol-reducatse) to spin the odorless precursor cinnamic acid into distinct, potent volatile phenols- like the reeky stinkers annotated above. It is these ethyl-phenols that are responsible for the funkiness that we smell- and what the experts smell, too.
So imagine sitting around a formal wine tasting in the swanky offices of Wine Spectator Magazine ranking and tasting old Burgundies. The conversation goes something like this, "Do you smell shit yet?"
"Nope, not yet. Maybe sweaty, or even musty, more like Matthew McConaughey after Bikrams yoga."
"Really? This one smells especially crappy to me, as in poop-crap, like merde and manure. Maybe you should get your sensory threshold recalibrated."
Yes, it's true, wine scientists have terms for this stuff. The "perception threshold" is the minimum concentration at which stank is identified in a dilute alcohol solution by 50% of "trained tasters." The "recognition threshold" is the same as the perception threshold but in actual wine. Adding stench to stank (if such an aphorism exists), the "preference threshold" is the concentration above which the overall aroma of a wine is affected. Maybe "compromised" is a better word, as in "smells like someone crapped on a grapevine." But even so, Brett abounds. Ribereau-Gayon's tome cites a study where almost 30% of red wines analyzed contained volatile ethyl phenol concentrations above perceptible thresholds (which happens to be 440mg/L).
So let's break down the science since it has some interesting corollaries. First of all, a pungent mustiness (i.e. an odoriferous volatile phenol) that is offensive to 50 out of 100 people may not even be noticeable to the remaining 50 sniffers. A pregnant lady's tolerance for off odors is certainly more nuanced than that of a pack of rowdy, football-watching, beer guzzling, chili and bean eating Steelers fans (who are obviously stinkier than Chargers fans). And what if some folks dig the Brett profile? Yes, science has proven that Brett is a wine fault that detracts from the intended fruity character of your favorite beverage, but still, rankest stench to one is fine perfume to another (and some very famous winemakers would agree). This is why wine is great.
And while we're at it, let's save Wine Spec some big bucks in these trying economic times. Lest the bottom line fall on wine consumers everywhere, we can dispatch our own dream team of low cost, expert merde detectors. Just bring in the mommies. Next time you're at the playground or your kid's gym class, just wait until inevitably one mom turns to another to exclaim, "You smell that? Some kid has a dirty diaper, and it's not my baby." How do they do that? What exactly is the perception threshold of a dirty diaper? And just how much of an elite trained smeller does one have to be before developing the olfactory synapses to correctly identify another child's poop from your own?
Epilogue: For all of you poop-centric, immature, Beavis and Butthead fans, "bunghole" is a technical wine term. It refers to the hole bored on the side of a liquid-tight, wooden barrel. Its stopper is called a "bung." When the bung is adequately tightened and submerged beneath the surface level of the aging wine, the barrel is considered impermeable to ambient oxygen.