It was far from preordained that an herbal elixir made by taciturn Carthusian monks since the 16th century would become a modern backbar staple.  Yet “monk juice,” as Pouring Ribbons proprietor Joaquín Simó calls it, has evolved from a bit player, modifying drinks in dashes and drops, to a star ingredient over the course of the cocktail revival, becoming indispensable to the bartender toolkit along the way.

“There’re 130 ingredients in it,” explains Simó, who has assembled a collection of vintage Chartreuse at his bar in New York’s East Village, of the liqueur’s appeal. “You instantly make your drink more complex by adding a teaspoon of it.” And for much of the past two decades, that’s exactly what bartenders have done, adding the nuanced ingredient in minute quantities or even just as a glass rinse. But much like Fernet-Branca, which transformed from a scant presence into a full-fledged base spirit, Chartreuse has landed increasingly large roles in today’s cocktails.

Although Chartreuse predates even the 1800s golden age of cocktails, in the context of the modern-day cocktail revolution, most point to Murray Stenson’s 2004 revival of the then-obscure Last Word—and its subsequent variations—as the drink that brought the liqueur back to relevance.

Simó’s modern classic, the Naked & Famous, for example, is a mashup of the Last Word and the Paper Plane, Sam Ross’ own modern classic spin on the Last Word. In Simó’s, mezcal, Aperol and lime juice are matched with yellow Chartreuse.

Though the primary expressions of Chartreuse—yellow and green—both spotlight similar herbal profiles, they’re not exactly interchangeable. Assertive licorice and pine notes lead the green Chartreuse, while the yellow version is often considered more mellow, with a honeyed sweetness. Further, the green is much higher proof: 55 percent ABV, compared to 40 percent for the yellow.

“The sheer intensity of green Chartreuse can overwhelm,” Simó says. “I use green when I want to raise the volume, yellow when I want to turn it down.”

It’s yellow Chartreuse that adds depth and dimension to Michael Fifelski’s Golden Phone. A stirred riff on the 21st Century (Jim Meehan’s tequila-based update of the classic 20th Century), the drink calls for half an ounce of yellow Chartreuse as an herbal bridge between tequila, Lillet and crème de cacao.

The pronounced anise notes and higher proof of green Chartreuse, meanwhile, often relegate it to a scant measure. “It’s not for the faint of heart,” says Kenneth McCoy, proprietor of New York’s The Rum House. McCoy favors the minimal approach in drinks like his Barrymore Cocktail, in which green Chartreuse glazes the glass of an otherwise-austere Scotch-based drink. He then ignites the overproof spirit before the drink is poured into the coupe, extinguishing the flame.

While the “gravitas” and “mystery” of a secret-recipe elixir made by monks may have cemented it as a bartender’s handshake originally, McCoy says, more casual applications will be what carries Chartreuse forward, whether that means shots of the liqueur (a staple at Baltimore’s Idle Hour) or Chartreuse on tap (as seen at The Passenger in Washington, D.C.), or more irreverent use in cocktails.

One of the earliest examples of this playful approach to using Chartreuse in cocktails was the Chartreuse Swizzle, which includes a whopping ounce and a half of green Chartreuse shaken with spiced Velvet Falernum and pineapple and lime juices, yielding a tropical effect. Created by Marcovaldo Dionysos, the drink debuted at Harry Denton’s Starlight Room in San Francisco, eventually gaining popularity at Clock Bar circa 2008. The drink unleashed a green-tinged avalanche, contributing to a surge in Chartreuse sales in the early 2000s, according to Tim Master, who has represented the brand since 2011. Cementing the ingredient as more than a modifier, the Chartreuse Swizzle likewise signaled the arrival of a new wave of Chartreuse-laden drinks.

The drink went on to pave the way for cocktails like Erick Castro’s Piña Verde, aka the “Greenya Colada,” a modified Piña Colada built on a base of one and a half ounces of green Chartreuse; or the Chartreuse Slushy at San Francisco’s The Morris, where Paul Einbund blends an ounce of green Chartreuse with tart lemonade and palm syrup.

This more relaxed usage of Chartreuse is the wave of the future, says McCoy. “When I first started using it, going back over 10 years, there was a bit of a highbrow thing with it, to be honest,” he recalls. “We’ve moved past that. It’s no longer, ‘This is how it’s used.’ Instead it’s, ‘Why not? Maybe it’s great with pineapple juice!’”