In the world of cocktails, everything old is new and trendy again. And yet, few products have been revived as dramatically as bitters.

Despite the relative obscurity of the flavorful extract that is a staple of drinks like the Manhattan over the last century, the craft cocktail movement has inspired dozens, possibly even hundreds of upstart brands of bitters.

First, some history. Bitters are rooted in both herbal medicine and bar culture. Before the advent of pharmaceuticals, bitters were commonly sold as cure-alls. "None of them were disease-specific," said Sother Teague, beverage director of the bitters tasting room Amor y Amargo in New York.

But the line between medicine and recreation was blurry, at best. Bartenders used bitters to make drinks more complex, but prescriptions for booze or specific cocktails were also quite common. "We weren't super good at science back then," said Teague.

The abundance of bitters came to a halt with the Pure Food and Drug Act of 1906. With one pen stroke, most brands were put out of business. Between that law and Prohibition, bitters pretty much disappeared.

Until early aughts, bitters was almost a one-brand category. Angostura—with its distinctive, oversized label—was virtually the only name in the game. But even that mainstay wasn't always so easy to find, said Noah Rothbaum, founder of Liquor Intelligence.

With the craft cocktail boom, even market leader Angostura began changing to cater to the times. In 2007, the brand introduced its first new flavor, Angostura Orange. This year, it rolled out Amaro di Angostura, a liqueur based on its signature bitters.

Angostura's first bitters product, affectionately known as "Ango," spawned the nigh-universal aromatic bitters category. An estimated 750,000 bottles were sold in the U.S. in 2009.

"It's almost like Kleenex," said Rothbaum. Angostura "has transcended a brand name and is almost a category name."

Despite the revival, a lot of damage was done during those darker times. "[Bitters were] gone for so long that we had several generations of drinkers who were never really exposed to bitters," explained Rothbaum. But educating the drinking public is a part of the craft cocktail movement, Teague pointed out, and "that certainly involves bitters."

Despite its dominance, Angostura does have its competitors. Among those that have a sizeable following are Peychaud's (the bitters used in the New Orleans-born cocktail, the Sazerac), Scrappy's and Hella Bitters.

Since bitters, like baking extracts, are considered nonpotable alcohol, they are sold in supermarkets and specialty shops. But the "market is fairly limited," noted Rothbaum. "You're only using a few dashes at a time."

To compensate, some companies are marketing smaller packaging. Instead of selling to bars, they are presenting their products at specialty shops and trade shows. This model has worked for New York-based Hella Bitters (full disclosure: co-founded by Adweek product manager Eddie Simeon), which was the focus of a recent American Express spot.

"[Ango's ads] haven't changed in terms of content," said Greg Boehm, CEO of barware purveyor Cocktail Kingdom. The strategy was somewhat different at the beginning of the 20th century. Instead of focusing on print ads, promotion included small recipe booklets with each bottle. Later, the booklets were sold separately. "All these bitters companies and spirits companies have circled back to that approach," added Rothbaum.

Everyone in the industry has a different vision of what's ahead for bitters. But no one thinks they're going anywhere.

In Rothbaum's words: "Just as we've seen with flavored vodkas, some of them will be popular for a while and then go away; others will become mainlines. It wouldn't surprise me if we saw a few types of bitters catch on and become part of the pantheon of drink legacy."

This story first appeared in the Sept. 21 issue of Adweek magazine. Click here to subscribe.