Third wave coffee shops have been playing around with carbonated coffee for years, from nitro cold brew to coffee tonic, so it should come as little shock that this summer's trendiest coffee drink is yet another type of carbonated cold coffee known as coffee soda. But what is coffee soda, exactly? The easiest way to describe coffee soda is as carbonated iced coffee, but this drink is often more complex than that. Imagine an iced coffee cocktail except without the booze—not the bottles of jet-black Manhattan Special, the OG coffee soda that's been manufactured in Brooklyn, NY, since 1895.

And this is part of the confusion about this summer's trendiest drink. Unlike a latte or an Americano or even nitro cold brew, there is no one standard coffee soda recipe or way to make it, so every coffee shop makes their coffee soda a little bit differently. At most places, the coffee itself won't actually be carbonated. Instead, coffee soda is a shot of espresso or a serving of cold brew that's finished with seltzer water. There's often some citrus added, be it a twist of orange peel or a splash of fruit juice, along with some sugar or syrup.

A few companies are trying to recreate the cafe coffee soda experience in a can, including Keepers Coffee Soda. Like Manhattan Special, Keepers is also made in Brooklyn, NY, but that's about where the similarities end. According to Grub Street, Keepers is a cold brew-based soda, "with some sugar, lemon juice, lime juice, tangerine juice, and tangerine oil." There's also Upruit Coffee Soda, which is also cold brew-based, and comes in either lemonade or tart cherry flavors.

One company that straddles both of these worlds—the coffee shop and the can—is Matchless Coffee Soda. The company's founder Nathanael Mehrens is often credited with starting the modern coffee soda trend in Nashville, Tennessee, while he was working at Crema. Back in 2012, Mehrens was running the coffee shop's beverage program and wanted to find a way to "push the refreshing qualities of iced coffee, and my first thought was carbonation." After toying around with different types of coffee and techniques for carbonation, he developed the recipe for coffee soda that's now known as Matchless, which is still served at coffee shops and restaurants across Nashville from giant kegs on draught lines.

Unlike most other coffee sodas, Matchless starts with flash-chilled coffee, which is to say hot coffee that is rapidly chilled rather than cold brewed coffee or espresso. (The coffee is now made and chilled at a local brewery called Fat Bottom Brewing on beer-brewing equipment that's been retro-fitted with custom parts to accommodate coffee.) Matchless is also different because this iced coffee is carbonated rather than diluted with soda water, and sweetened with demerara sugar.

"There still isn’t anyone that we’ve been able to find that’s doing it the same way that we’re doing it," notes Mehrens. "There’s people who are adding fruit juice to it, or there are people who are doing an espresso or a cold brew or those kind of things, but no one that we’ve been able to see is doing a genuine, flash-chilled iced coffee that’s carbonated with no extra additive stuff."

Matchless is now hoping to can this original recipe, which is still served at Crema and on draught at a bunch of cafés around the southeast, and finally sell it to fans across the country. And there's definitely demand for this coffee soda. The Nashville company launched a Kickstarter campaign, which has already exceeded half its $36,000 goal in less than ten days. Clearly, sweet and bubbly coffee soda, regardless of who makes it, is in—and hopefully here to stay.