As bourbon continues to boom, whiskey enthusiasts are clamoring for new products to enjoy. To satisfy these whiskey consumers, Louisville, Ky.-based Orphan Barrel Whiskey Distilling Co., a division of Diageo plc, released its Rhetoric 21-Year-Old Kentucky Straight Bourbon Whiskey.

An experiment in maturation, Rhetoric is re-released annually to explore the flavor characteristics imparted by each additional year the bourbon spends in wood, allowing for side-by-side comparisons, the company says. Aged in charred American oak barrels for one year longer than last year's 20-Year-Old release, this rich, complex bourbon represents an evolution in the progressively aged Rhetoric series, it adds. Throughout the process, the base Rhetoric liquid remains unchanged, with progressive aging expected to continue through the release of Rhetoric 25-Year-Old in 2019.

The Orphan Barrel was created in 2014 to find and share forgotten barrels of whiskey with discerning adult fans, who are encouraged to sip responsibly. Rhetoric 21-Year-Old follows five previous Orphan Barrel bourbons: Barterhouse (20-Year-Old), Old Blowhard (26-Year-Old), Rhetoric (20-Year-Old), Lost Prophet (22-Year-Old) and Forged Oak (15-Year-Old).

Rhetoric stocks were found at the Stitzel-Weller Distillery in Louisville, Ky. The bourbon was distilled in 1993 at the Bernheim Distillery in Louisville, Ky., while owned and operated by United Distillers. Rhetoric 21-Year-Old is hand bottled in Tullahoma, Tenn.

"The progressive aging experiment we're employing with the Rhetoric series is incredibly unique," said Ewan Morgan, Master of Whiskey for Diageo. "We're going to be able to compare a line of bourbons side-by-side to see how aspects of the liquid — color, aroma, flavors and mouthfeel — are impacted by extra time spent in the barrel. Like many others, I'm looking forward to tasting what one extra year in the barrel does to these bourbons over the coming years."

Compared with last year's release, Rhetoric 21-Year-Old is richer and more complex, with a fuller mouthfeel and slightly higher proof of 90.2 (45.1 percent alcohol by volume), the company says. Aromas of cherry, sweet tobacco, honey and leather build upon the oak, fruit, vanilla and caramel of last year’s Rhetoric 20-Year-Old. New tasting notes of sweet tobacco, dark chocolate, baking spices and honey complement the charred wood, caramel, vanilla and black pepper spice of Rhetoric 20-Year-Old, the company says. Rhetoric 21-Year-Old will be available nationwide in allocated quantities for a suggested retail price of $100 for a 750-ml bottle.

The packaging for Rhetoric 21-Year-Old features a wood-grain label with gold accents, elaborate typography and imagery of a hummingbird, the company notes. The background, reminiscent of the oak barrels in which the whiskey has aged, will become darker as each new, more mature offering is released.