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In 1845, herbalist Bernardino Branca was trying to treat cholera in Milan, Italy. He concocted what may be the first fernet — an Italian type of amaro, or bitter herbal liqueur — using 27 herbs, roots, and spices.

Little did he know, his recipe would remain intact for nearly two centuries and lead to the popular amaro Fernet-Branca.

“Fernet-Branca was born more as a medicine and not as a spirit,” sixth-generation heir Edoardo Branca tells CNBC. Today, the bitter is universally popular in Argentina and gaining popularity in the US, particularly in San Francisco, where it was sold legally during Prohibition because of its medicinal properties.

“In the United States, we were the only spirit that was still sold in pharmacies because we were sold as a cough syrup,” says Branca, who recently moved from Italy to San Francisco to help expand the family brand. “When Prohibition finished, I think my great-grandfather was one of the only people that was really, really sad about it because we were the only spirit in the United States without having any competitor.”

Fernet-Branca is particularly familiar among craft bartenders. “It’s the bartender’s handshake,” a spokesperson for the brand tells CNBC. “If a consumer were to belly up to a bar and order a Fernet-Branca, they’re immediately taken seriously and looked at in a different way by the bartender.”

Fernet’s renaissance can be credited to a couple of things, says Branca. One: the recipe, which remains a secret. “The recipe has been a secret for the past 172 years,” he says. “It’s something really unique — we have 27 herbs coming from all around the world — and this created a lot of buzz around the product.”

“It’s a real, real bitter, so there is practically zero sugar inside,” Branca continues. “In the past 10 to 12 years, we have seen a lot of the English-speaking countries starting to want to drink something a little more herbal and bitter. I think people are starting to want something that is a little bit better for you. Not everyone wants a cocktail or a drink that is completely full of sugar.”

Plus, Fernet-Branca consumption supposedly comes hangover-free.

Secondly, the company adheres to its motto since day one: “Novare Serbando,” which translates to, “renew, but conserve.”

In other words, the company continues to adapt to keep up with consumer market trends and needs, says Branca, but preserves its process, values, and ultimately, its recipe.

The Branca family understands the importance of constantly innovating and adapting. After all, to last more than 170 years, there’s no room for complacency.

Of course, some traditions may never change, such as the secret recipe. It’s been in the family for 172 years and it’ll stay that way, says Branca.