During a recent dinner service in one of the two restaurants where I currently moonlight as a sommelier, a server approached me with a question that caught me off guard. A guest at one of his tables wanted to know which of our Amari would be best in his coffee. “In his coffee?!,” I balked, before quickly springing into restaurant problem-solving mode. Of course we would bring him whatever he wanted to fortify his espresso; it’s not as though this was the first unusual request a diner had ever come up with. And why was it so unusual, anyway? There have always been drinks comprised of uppers and downers in tandem. Take the Italian caffè corretto (which blends a shot of espresso with a small amount of Sambuca or a Grappa or other brandy), the Spanish carajillo (which adds rum to the list of accepted dosers), Irish coffee (which involves whiskey, sugar, and a thick layer of cream), or the numerous other cultural staples for caffeinated concoctions. What was it about this particular suggestion that bothered me?

As someone who loves both coffee and the bitter Italian digestivo, I couldn’t see myself ever wanting the two in the same glass. I abide by the old adage for food and wine pairing: a perfect match emphasizes neither one nor the other – it elevates both. And as for cocktails, the best I have encountered have been greater than the sum of their parts. A quick review of our amaro selection left me with more questions than answers. Most of the examples that we had in house were of the more fragrant, ethereal variety (Montenegro, Nonino), which I feared would get lost completely under the intense torrefied flavors of coffee. Amaro Ramazzotti might work, since it’s darker and concentrated enough to hold its own; its red spice-inflected notes could add an interesting dimension to the hot beverage. But it was clear that you couldn’t categorically decree that amaro mixes or doesn’t mix well. The rules of coffee-booze blending are more complicated than just the booze type. So I polled a few of my industry compatriots for their thoughts on what works, what doesn’t, and if the rules have changed at all in the current state of coffee culture.

Quality, it turns out, is the first condition that everybody names. “This is exactly the same thing as the Boilermaker issue,” says Nicolas Palazzi, owner of PM Spirits, an artisan spirits importer. “When you’re in college, you might order a Miller Light and a Beam White Label. Dumping subpar product into subpar product is fine – it gets one buzzed. Goal attained. Now, there should be a law against dumping kickass whisky into an awesome craft brew.” For coffee, he advises a “neutral spirit or brown distillate,” but nothing too rare or characterful that could be stifled or even ruined by mixing. Taylor Parsons of République in L.A. echoed the same concern for high-quality products. “Don’t use bathtub gin,” he says, “but I would hesitate before adding a shot of Laberdolive.” Gramercy Tavern beverage director Juliette Pope stipulated that the quality of the coffee and the quality of the spirit be proportionate, since “cheap versions of either espresso or spirit will take away from the whole.”

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The second condition was finding a middle-road spirit – something neither overtly aggressive nor too delicate. “Stay away from anything too bitter or astringent,” notes Parsons, “things like peaty scotches.” Jeff Porter, beverage director for the Batali & Bastianich Hospitality Group in New York adds, “with Grappa, don’t use the aged versions or anything too pure or fine,” sharing my misgivings about squandering a product’s nuance. Parsons finds that “the baseline flavors of espresso make the most sense with contrapuntal pairings,” that is, spirits with sweet or floral tones or those with viscosity. He has himself enjoyed Spanish brandy. Pope has discovered the joys of St. George’s NOLA Coffee Liqueur and allspice dram “to take things in a more winter-warming direction” and has been known to dope with kirsch when she’s in Switzerland. (“When in Rome…”) And if pressed, Palazzi would drink “something with residual sugar, like rum of the El Dorado type that would sweeten the espresso and add aromatics.”

Dosage was universally mentioned, since balance is a quality that most sommeliers extol. “A full shot of anything is too much,” says Parsons, “unless you are drinking coffee out of one of those huge 32oz. trucker mugs.” The preferred method of serving the spiked beverage is to serve the coffee and spirit separately, allowing the guest to calibrate to his or her desired strength. And with the coffee landscape in this country changing, favoring with more frequency lighter extraction methods like pour-over, the possible range of spirit additions is expanding – those aforementioned more delicate products finding their balance with more feminine, high-toned brews. “Our coffee, both drip and espresso, has for sure headed in that lighter, brighter, more aromatic direction,” says Pope. “I am not sure that I’d want something super thick, rich, and bitter to go in those.” Reflecting on the amaro quandary, she suggests that Santa Maria Al Monte might overpower delicate styles of coffee—but something flavorful like Ciociaro or that Ramazotti could be just right.

The overarching rule is to of course drink what you like. The suggestions listed here are based on a combination of historically proven pleasures, trial-and-error, and pure hypothesis. The guest that night was content with a strong, black cup and a side of fernet–its perfect sparring partner of “full-frontal bitter” (Porter’s words). I will continue to keep my amaro and coffee separate but plan to experiment over the fall and winter seasons, and–who knows–discover a new postprandial favorite?