It seems that much of foodservice’s focus is on flavors that are sweet, salty, and savory, but there’s something to be said for ingredients that bring the tastes of bitter and sour. Just as composers add minor chords and dissonance to their works to give them a certain tonal quality, chefs do the same with bitter and sour characteristics.

“They accentuate the authenticity of cuisine,” says John Csukor, president and chief executive of KOR Food Innovation, a culinary and marketing agency based in Ashland, Virginia. “Those flavors are providing the notion of balance [to dishes].”

It’s not as if bitter and sour flavors haven’t been popular in the U.S. Coffee, the most consumed beverage in the country, is bitter, as is dark chocolate, which has been gaining in favor. Vinegar and lemon are sour and are almost always included in chefs’ pantries.

Barbecue, meanwhile, “is filled with bitter and sour,” says Csukor, who is a chef. Vinegar not only helps to break down meat during slow cooking, but it also provides flavor, as do bitter smoke and char, helping to round out the meat’s sweet and savory flavors.

“Traditionally, most American restaurants work very hard on salty and sweet flavors,” says Jesse Gideon, chief operating officer at Atlanta-based Fresh to Order. “Since the emergence of more global cuisine, we have seen more balance in flavors. … Bitter rounds out the whole palate. I can actually back off something salty and sweet by adding something bitter. That makes the salty and sweet stand out.” He adds that vinegar provides a sour taste “and gives you that rounded-out flavor in your cheeks.”

Chef Chris Koetke, vice president of Kendall College School of Culinary Arts in Chicago, calls bitter a fascinating flavor.

“Not one of us is born liking bitter,” he says. “It’s an acquired taste, but as this country has adopted new types of cuisines, we’ve become much more interested in bitter as a desirable taste.”

Bitter flavors from coffee also show up in some desserts, such as in frozen yogurt or milkshakes, while dark chocolate is part of hot and cold coffee beverages, numerous desserts, and mole, a Mexican sauce.

Sour is even more common, from a slice of lemon served with fish to vinegar with a slaw, Koetke adds. “It comes down to a question of how sour you make it,” he says. “There has been a big uptick in people’s desires for sour because it brightens a dish.”

For Modern Market’s Nate Weir, chef and director of culinary operations, sour is also important for guests who desire to eat healthier because “it helps to cut the richness factor of foods” while adding brightness and complexity to dishes.

“People are looking for authentic ethnic flavors,” he says, and sour and bitter flavors play into that. “Five or 10 years ago, you talked about fusion, but you don’t hear that much anymore. It was a way to introduce people to different foods, but now they want real.”

Bitter and sour, along with the other three primary flavors—sweet, salty, and umami—have been part of quick-service restaurant cooking from its earliest days. White Castle hamburgers have featured a pickle chip since at least the 1930s, according to company records.

“Putting a pickle on a hamburger or sandwich creates contrast and more flavor,” says Philip Bach, corporate chef and head of product innovation at the brand. “A burger has an umami flavor, so if you add a sweet, sour, or garlic pickle, you’re getting another taste receptor going. You get some texture from the caramelization or char of the burger, but a crisp pickle is another point of differentiation.” As customers’ seek more vibrant experiences, Bach says, he’s looking at ways to provide not only spicy and hotter items, but bitter and sour ones as well.

Younger diners have become more receptive to these flavors because they have been exposed to a wider array of ethnic foods.

“The international influence has become increasingly prevalent,” Csukor says. “Southeast Asian cuisine, which features many bitter and sour notes, has risen to a height of popularity, so much so that it is refining into regional tastes.”

Sweet and sour has long been a Chinese combination, with rice vinegar providing the sour flavor. These days, sour can be found in anything from Korean kimchi’s fermented vegetables to Thai cooking that has sour notes from lime and tamarind.

“Every vegetable can be pickled,” Csukor says. He adds that you can quickly make a Korean burger by making it with kimchi, or a Japanese burger with daikon.

Add in Latin and Mediterranean foods and “we’re seeing the concentric circles have broadened, opening us up to more authentic, more refined cuisine, allowing chefs to explore those flavors more realistically,” Csukor says.

“You go to Mexico and there are limes on every table,” Kendall’s Koetke says. The citrus and other acids used in Mexican cooking “are what brighten the dish, brings out the flavors, and makes a dish not heavy.”

Torchy’s Tacos has several items that embody bitter and sour flavors beyond citrus, including pickled onions and jalapeños, says Michael Rypka, the Austin, Texas–based company’s founder and vice president of culinary and marketing. There’s also escabeche, which is fish marinated in an acidic broth. Not only do these ingredients layer well, but they also “complement a dish largely by cutting the heaviness of a protein, which provides a fresh balance for the overall flavor,” he says.

Taylor Gourmet has created several ethnic-influenced hoagies that play with bitter and sour tastes. For its seventh anniversary, the Washington, D.C.–based fast casual teamed up with well-known local chef José Andrés to make a limited-time sandwich whose proceeds were donated to Andrés’ nonprofit World Central Kitchen to benefit Haiti.

The Griot Picklese hoagie was based on a Haitian staple. The griot—spicy pork shoulder—was braised with sour orange and habanero, while the picklese, or pickled vegetable slaw, included onions, green peppers, carrots, serrano chiles, cabbage, and spices.

“You’ve got some amazing flavors, with sweet and heat in the pork and sour and tangy with the picklese,” says Taylor Gourmet cofounder Casey Patten. He adds that there is additional sweetness from a caramelized plantain spread.

Patten also worked with another D.C. chef, Danny Lee of Mandu, for a Korean cheesesteak special. The KimchiSteak sandwich featured slices of a bulgogi-style ribeye steak with sour grilled kimchi, aged Cheddar cheese, sesame seeds, and scallions.

“We put that sandwich together as a commemorative piece” marking the first year of offering cheesesteaks on the concept’s menu, he says. “We didn’t know how it was going to be received because a lot of things were going on there, but people loved it.”

One of the chain’s most popular limited offerings is brown sugar–roasted pork loin with mashed sweet potatoes and caramelized onion apricot chutney. “We use a ridiculous amount of vinegar in the chutney,” he says, with the apricots, raisins, cranberries, and other ingredients cooking down to a jam-like consistency.

Koetke points to the growing popularity of bitter greens like kale as proof that customers are embracing bitter flavors. “Go back 20 or 30 years, and the only greens in salads were romaine and iceberg,” he says.

Sascha Weiss, culinary director for San Francisco’s The Plant Café Organic, says kale is an interesting ingredient to play with on a limited-service menu.

“It is quite bitter, but as foods become in vogue or get in the spotlight, they become in demand,” he says. “Ten years ago, you couldn’t sell it.”

Kale, like other dark greens, has become popular due to its perceived health benefits, and The Plant Café Organic offers it in juices, smoothies, and several salads. Its arugula and grapefruit salad mixes bitter and sour ingredients with a macadamia nut dressing.

At Modern Market, where salads account for about 40 percent of sales, six different vinegars are used to achieve certain flavors in vinaigrette. Weir calls his lemon-maple vinaigrette “a secret weapon” because the sweet and sour dressing is used in so many different applications beyond salads, including a sausage pizza with wilted escorole.

Beverages are an approachable way to work with bitter and sour flavors, not only with various types of coffee, juices, and smoothies, but also in soft drinks and beer. That’s especially true of craft beer, which shows up at an increasing number of limited-service restaurants. India pale ales, with more bitter characteristics, are the most popular craft varieties, according to statistics from the Brewers Association.

Bitterness in beer comes primarily from hops—flowers of the hop plant—and from malts roasted in higher heat, says Julia Herz, craft beer program director for the Brewers Association.

“Bitter should not be looked at as a negative,” she says. Just as tannins, acidity, and sweetness need to be balanced in wine, “bitterness does the same in beer.”

Lemonade is the most popular sour drink and is served many ways. Fresh to Order’s Star Anise Lemonade not only has lemons and sugar, but also star anise and spicy bitterness from mint and licorice, which “lets you appreciate the sourness and sweetness,” Gideon says.

Modern Market and other concepts are selling kombucha, a fermented tea drink. “It’s described as sour or bitter, and has those underlying flavors,” Weir says.

Kombucha is also on the menu at The Plant Café Organic, where it’s available in kegs and bottled, either green or with herb and fruit syrups such as tarragon and grape.

“We also use that product for gastriques—it pairs well with huckleberries,” Weiss says. “We did a duck dish with that and we also did one with lobster.”

Just as bitterness balances sweetness, it works the other way. Csukor, who consults for the National Honey Board, says honey helps mask astringency because its viscosity coats the tongue while still allowing the flavor. Meanwhile, restaurants are increasingly using a wide variety of pickled items, including onions, carrots, jalapeños, and other vegetables. Modern Market does some of that pickling in-house.

The most common pickled items are cucumbers—base for the standard pickle—and Lakewood, Colorado–based Good Times Burgers and Frozen Custard began an in-house pickling program last summer to make dill pickles.

“In each store, we set up production for wavy cut pickle chips to use on any sandwich and for deep-fried pickles we sell as a side,” says Kit Mitchell, director of franchise operations. “Each store, two times a week, will make a bucket of pickles.”

Pickling may be unorthodox for a quick-service burger chain, but when Good Times looked at ways to make a difference with its burgers in terms of condiments, pickles were the ones that would both resonate with customers and work operationally.

Making pickles in-house also blends with Good Times’ philosophy. “One of the fundamental pieces of our business is to have handcrafted menu items when possible, so pickles really support that,” he says. And they have been simple to make.

“They’re kind of a background ingredient built into sandwiches, so some people don’t notice,” Mitchell says. “But most customers have shown they appreciate that the pickles keep burgers tasting good and are of a higher quality.”