They go by nicknames like Donut, Split Label, Pewter Top and, most amusingly, Cheesy Gold Foil. They’re oily in mouthfeel, with a floral perfume on the nose and a taste that has been described as “antique leather,” “fragrant pipe tobacco,” “damp mustiness” and even “blue cheese.” More often than not, though, that indescribably complex profile is simply called “Wild Turkey funk.”

While today, the Lawrenceburg, Kentucky, brand is often seen as bottom-shelf, drinkin’-in-the-woods-type whiskey, the bourbon cognoscenti have always known otherwise. Many believe the flagship Wild Turkey 101 isn’t just a thrifty buy, it’s also world-class. But it’s the old, off-the-market bottles of Wild Turkey (known as “dusties”) that have lit up the online whiskey-collecting forums.

Bottles like 1980s Beyond Duplication and 1990s Kentucky Legend now command huge prices on the black market, with many claiming they are better than any Wild Turkey released today. This is particularly interesting because, while vintage bottles from such defunct distilleries as Old Taylor and Stitzel-Weller (the progenitor of Pappy Van Winkle) remain highly coveted, no other still-active Kentucky distillery has such a devoted following for its old products.

This fandom has mostly developed online, especially on forums like Reddit where users try to explain, sometimes half-jokingly, what exactly dusty Wild Turkey tastes like. David Jennings is a Wild Turkey enthusiast who blogs under the name “The Rare Bird.” After acquiring and tasting numerous samples of Wild Turkey 101 as old as the early-1970s, he sketched out a Venn diagram comparing how dusty (“sweet herbs & spice”) and modern (“’nutty’ toffee”) bottles differ while still maintaining the classic Wild Turkey notes of “rich vanilla” and “musty oak.” Others think it’s the fruitiness that is crucial, going from a plummy, port wine-finished taste in pre-1990s bottles to one more citrusy and bright today.

But what exactly created this unique flavor in the past?

Unlike wine or beer, whiskey doesn’t age, though slight oxidation is possible, depending on cork quality. (Wild Turkey is known for having crumbling, sub-par cork stoppers, which is sometimes cited as a potential culprit for its unusual flavor profile.) Still, for the most part, what a vintage whiskey tastes like today is what it tasted like back when it was bottled. And whatever master distiller Jimmy Russell was distilling in the 1970s and ’80s is unlike anything out there now, though many folks aren’t exactly sure why.

Noted bourbon historian Mike Veach wrote an extensive blog post trying to explain the unique flavor found in vintage bottles of not just Wild Turkey, but any “old” bourbon, ultimately noting that it could have been a variety of factors from copper stills to lack of water treatment to smaller barrel size. But everyone has a theory about what causes the Wild Turkey funk; I’ve heard everything from a secret change in yeasts to a switch to automated equipment to wider “cuts” being taking in the distillation process to “bottle conditioning”—i.e. how UV light and air effects a poorly-stored bottle over the years.

Jennings, for his part, thinks the lowering of urethane levels (by law) in 1989 might be a critical factor no one considers. Urethane is a cancer-causing crystalline compound formed naturally during fermentation, found in particularly high levels in older bourbon, which is said to product a bitter flavor. “I’d imagine [urethane] to be part of the old bottle taste, or mouthfeel at the least, but no one’s talking about urethane levels,” notes Jennings. “It’s apparently second only to alcoholism in spirits industry taboo.”

For what’s it’s worth, the entire Russell family knows about the buzz their old products elicit online. Jimmy’s son and current master distiller, Eddie Russell, told me he and his father unfortunately do not maintain an archive of past products, and haven’t since the Pernod Ricard acquisition in 1980 (today Wild Turkey is owned by Gruppo Campari). But it wouldn’t matter; he doesn’t think they are much different from what he’s producing today.

“Biggest difference is that back in the ’70s and ’80s everyone had excess whiskey because it wasn’t too popular, so there was older whiskey in the blends from excess stocks,” Eddie Russell explained during a recent Reddit AMA, noting that now that bourbon is way more popular, age statements are way more accurate. (A bourbon age statement must legally list the youngest barrel used in a blend.)

Eddie Russell further told me the company’s recipes, yeast and processes haven’t really changed since he started working there in 1981. Though, the “entry proof” of liquid going into the barrels was raised from 107 proof to 110 proof in 2004, and then to 115 proof in 2006—something that many think has gradually changed the flavor profile over the years. (Higher entry proofs are believed to create more grainy flavors.)

Eddie Russell does note that back when he started at the distillery, they still used cypress fermentation tanks, only switching to more modern stainless steel ones in the early 1990s. (“It took Jimmy eight years of testing the stainless tanks to feel comfortable switching, to make sure it didn’t change the taste,” he told Reddit.) Installed around 1925, Wild Turkey’s cypress tanks were literally made of virgin-growth cypress wood planks. Porous wood is obviously harder to clean than stainless steel and thus, as Veach notes, “there may have been more bacteria influences on the whiskey.”

The bourbon collector and producer of California Gold, Danny Strongwater (not his real name), believes it’s self-evident the Wild Turkey funk comes from bacteria created by old, possibly dirty equipment and facilities. “That’s the yeast!” he exclaimed. “It’s developed its own chemistry.” It sounds akin to the Belgian lambic-makers like Cantillon who don’t ever clean the cobwebs in the rafters, lest they disturb their brewery’s delicate ecosystem of wild yeast and bacteria. While this theory seems most plausible to a beer geek like me, it doesn’t quite explain why Maker’s Mark, which still uses similar cypress tanks, doesn’t have their own signature funk.

Whatever the culprit, bottles that exhibit the Turkey funk have become increasingly rare. So called “dusty hunters” have been clearing Wild Turkey from shelves at off-the-beaten-path liquor stores for the last decade and a half. Finding even early-aughts bottles “out in the wild” has become near-impossible; forget about older, more coveted bottles. Today, most are bought and sold on the secondary market, where many of the bottles mentioned below sell in the $400 to $700 range, or trade straight-up for today’s big ticket items like George T. Stagg and William Larue Weller.

If that’s too rich for your blood, Eddie’s son and Wild Turkey brand ambassador Bruce Russell believes private barrel editions of the current Russell’s Reserve Single Barrel “can be very close to the old stuff.” Other modern analogs people often cite include the Japanese-only export Master Distiller’s Select, the recent Decades and Russell’s Reserve 1998.

The 1998 was released in 2015 at a fairly lofty suggested retail price (SRP) of $250. Like many high-priced, limited-edition Wild Turkey bottlings, consumers initially passed on it, and it lingered on shelves. Then, just last summer, around the same time that word begin to spread online that the 1998 embodied that enigmatic funk, shelves were quickly cleared and the bottle skyrocketed to three times its SRP on the black market.

Five of the Most Sought-After Wild Turkey Dusties

While dusty bottles of 101 will always remain a geek delight, a few other bottlings in the portfolio remain timeless, gaining esteem as the years go on. (For what it’s worth, Jennings hails a 1981 Wild Turkey 101/8 as the best he’s ever had, calling it “punchy and rich.”)

Wild Turkey Kentucky Legend (a.k.a. “Donut”)

Originally released in 1998 as a duty free product in Japan, it’s earned the nickname “Donut” due to its strange bottle shape. More significantly, it’s one of the only barrel-proof single-barrel bourbons the distillery has ever released, usually clocking in at around 115 proof. Intensely herbal, Jennings tells me, “Donut is, in my opinion, like dusty 101 cranked to 11.”

Wild Turkey Beyond Duplication

A 12-year-old bottling with apparently enough of a goofy moniker that it doesn’t require a forum nickname, Beyond Duplication came onto the market for a few years in the early-1980s. Eventually pulled from shelves in the U.S. to make way for Cheesy Gold Foil (see below), it remained a Japanese export until the late-1980s.

Wild Turkey 12 Year Old Gold Foil Label (a.k.a. “Cheesy Gold Foil” a.k.a. “CGF”)

The most ballyhooed bottle from Wild Turkey’s past, and certainly the most comically dubbed, Cheesy Gold Foil earned its nickname for its garish and cheap-looking 1980s-era packaging, even coming in an equally eye-injuring tube. The next in a long line of 12-year-old products produced after Beyond Duplication’s discontinuation, it was on the market from 1985 through 1992. Jennings notes it has a “very unique, oily mouthfeel.”

Wild Turkey 12 Year Old (a.k.a. “Split Label”)

Yet another incarnation of Wild Turkey 12-year-old, Split Label is so named due to its, well, bifurcated label. Released to the market in 1993, it’s one of the last Wild Turkey dusties to still garner much online discussion.

Wild Turkey Kentucky Spirit (a.k.a. “Pewter Top”)

Still a bottling in Wild Turkey’s portfolio, earlier releases of this bourbon, which debuted in 1994, are the most coveted. Though the current bottle shape (with glass meant to resemble a turkey’s fanned tail) is similar to earlier batches, dustier bottles can be recognized by their pewter cap (today’s is made of wood). A single barrel bottling, brought down to 101 proof, the flavor profile back then was of rich maple syrup; today it shows more of a citrus note with a hint of cinnamon.