If you go to a lot of cocktail bars, you might have noticed a bit of a revolution happening in recent years: Bitter is taking over. Campari, Fernet-Branca, Cynar and a rainbow of other bitter spirits are showing up on more and more menus.

These rich and complex spirits all fall into the same category, amaro. But here’s the problem: That category encompasses everything from the light and citrusy Aperol to the seriously tannic Amaro Dell’Erborista. So what is an amaro? It’s a liqueur (which means that it contains at least 2.5 percent sugar by volume), flavored with something bitter. The bitter ingredients can be anything under the sun, as can the sweetener and even the alcohol base. The name comes from Italy, as do most amari (that’s the plural of amaro), but they’re made all around the globe. How to make sense of such a wide and varied category? I turned to Sother Teague, the bitter-loving chef-turned-bartender (he used to work on Alton Brown’s Good Eats TV show) behind New York’s Amor y Amargo, which specializes in amari and cocktails made from them, for some advice.

The first thing to remember, Teague says, is that amari are both bitter and sweet. “It comes as a surprise to most laypeople that amari all have a sweetener. (This varies based on the maker’s goal and recipe, but common sweetners are sugar, burnt sugar, molasses, beet molasses and honey).”

Most amari have their roots in herbal medicine—the bitter ingredients were used as treatments for all kinds of ailments—and sweeteners were added to make the medicine go down more easily. To this day, they are most commonly consumed by themselves in their European homeland as aperitifs (to stimulate the appetite before a meal) or digestifs (to aid digestion afterward). It’s only during the recent rise of the craft-cocktail movement in the last decade or so that amaro cocktails became a thing. “The bulk of the world doesn’t drink cocktails at all,” Teague says. “It’s an American affectation to compulsively mix things.”

Unfortunately, amari can’t be very easily broken down into simple subcategories. “Amaro makers are shrouded in mystery and very protective of their often centuries-old recipes and methods. They’re a very tight-lipped bunch making it difficult to get any information from them,” Teague says. “There aren’t many specific categories, as each maker feels strongly that their product is unique.”

However, there is one clearly defined amaro subcategory: Fernet. These are the most hardcore of amari, turning both the sweetness and bitterness up to 11. They’re dark and syrupy in texture, intensely rich and herbal in flavor and typically high in alcohol. You’ve more than likely encountered Fernet-Branca, a minty version made in Milan that’s a favorite of bartenders and San Franciscans (and Argentines—Branca has a second distillery in Argentina just for the South American market), but there are lots of other brands. These include Fernet-Vallet, a Mexican favorite that’s even more bitter than Branca, as well as Letherbee Fernet, a recent creation by a Chicago distillery that’s a favorite of Teague’s (he calls it “super sharp and lush with aloe and eucalyptus”).

Beyond fernet, Teague mentally organizes amari into broad groups based on flavor, such as floral, herbal, woody and citrusy. That last group includes one cocktail lovers will recognize: Campari. The bright-red spirit is based on gentian, a root that goes into many aperitifs and has a bitterness that goes well with citrus peels. Campari has a nice grapefruit note that makes it refreshing despite its bitterness—a characteristic it shares with other gentian-based amari, including the light, low-alcohol Aperol, the orange-and-rhubarb Gran Classico and the floral and earthy Salers Aperitif. Any of these will make a delicious Negroni.

Another popular amaro you might have forgotten about is the frat boy favorite, Jägermeister. However, the German liqueur is quite sophisticated when you taste it at above-freezing temperatures. “People always think I’m kidding when I say that I love Jäger. But I’m not. It’s lush and rich. Lots of citrus, cinnamon, cardamom, anise and ginger,” Teague says. “In summer, I shake it with grapefruit juice and dry Curaçao for a Margarita variation.”

Want to get further into bitter? Teague’s advice is to train your palate. “Of the five flavors that we perceive—sweet, sour, salty, umami/savory and, bitter—only bitter is truly an acquired taste. This goes back to our biological imperative to perceive bitter as a poison,” he says. “I never push someone down a black diamond like fernet or Dell’Erborista on their first go; I start them on a bunny hill.” His favorite “beginner” amari include Amaro Nonino Quintessentia, which is light-textured, floral and a little spicy, and Amaro Meletti, which tastes of cola and leather.

Once you’ve gotten used to bitter, it’s time to dive in further and try some cocktails. Teague likes to mix Luxardo Amaro Abano, a fruity amaro with distinctive white pepper notes, with rye whiskey; Becherovka, a Czech digestif with cinnamon and clove flavors that “tastes like winter,” with apple brandy; and Amaro Nonino, a floral, grape-based bottling, with cognac. And if you want to go super-intense, mix Amaro Dell’Erborista, a hugely bitter and herbaceous spirit, with a powerfully peaty Scotch.

Perhaps the most versatile cocktail amaro, Teague says, is Amaro Montenegro. It’s a bit sweet, a bit bitter and a bit sour, and its balanced flavor pairs well with everything from rum to bourbon. At Amor y Amargo, Teague mixes Montenegro one-to-one with blanco tequila and a few drops of orange bitters to create something that tastes a lot like a bitter Margarita. He calls it The Full Monte.

Some amari just defy classification entirely. Cynar is an artichoke liqueur. It sounds crazy, but it’s getting mixological attention for a reason. The stuff doesn’t exactly taste like artichokes—it’s more of a grassy, earthy bitterness—but the ingredient “has the ability to temporarily suspend our perception of sweet,” Teague says. Thus, it makes a great partner for fruity spirits and liqueurs that can overwhelm with sweetness. Teague suggests a CIA: Cynar in apple brandy. Cynar also just blew some bartender minds with a new 70-proof edition (the original version is just 33-proof), which is even more cocktail-friendly.

Many of the classic amari have centuries of pedigree, but the new generation of American craft distilleries are trying their hands, too. Besides the aforementioned Letherbee Fernet, there are Fernet Leopold Highland Amaro and the Campari-like Leopold Bros Aperitivo from the excellent Leopold Bros. Distillery in Denver, and Breckenridge Bitter, an alpine aperitif designed to mix with beer. There’s even a distillery dedicated almost entirely to amaro: Seattle’s BroVo has created a series of amari in collaboration with bartenders, from John Ueding’s citrusy Amaro #1 to Mike Ryan’s chocolaty Amaro #14.

From bright and fresh citrus sippers to deep, dark spice bombs, the world of amaro encompasses a wide range of flavor. And it’s one you need to know about. So start drinking bitter.

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Jason Horn is Playboy.com’s spirits columnist. He lives in Los Angeles and you can follow him on Twitter @messyepicure.