Some bartenders list cocktail bitters as an optional ingredient in their drinks. Others would call this blasphemy and argue that bitters are crucial to a cocktail’s expression and je ne sais quoi, like the seasoning on your favorite dish or an exclamation point at the end of a sentence.

Mandatory or not, bitters can be found in every bartender’s arsenal, which means they can sit on a shelf or bar cart for weeks, months, or years at a time. And since they’re essentially a cocktail’s finishing touch, why would anyone want to screw that up by using expired product? That’s why when it comes to the uncertain shelf life of bitters, there are a few points that need addressing.

Bitters are made by infusing a neutral spirit or glycerin with any number of aromatics, such as spices, tree bark, fruits, or botanicals. From household names like Angostura all the way to Mexican mole bitters and truffle-infused iterations, the options are endless. (It’s worth noting that there’s a big difference between cocktail bitters and potable bitters, like amari, which are consumed in quantity. Cocktail bitters are so potent in flavor that they’re only used in drops or “dashes.”)

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Do Bitters Go Bad?

Just like most spirits, bitters don’t technically expire. According to Jon Adler, mixology wizard and bar manager at Shinji’s in NYC, most bitters, including Angostura, do not go bad since they generally have an alcohol content of about 45 percent ABV. “The alcohol [or glycerin] works as a preservative so they will never go rancid. But unless they’re kept in the fridge, they will change flavor over the years as alcohol does slowly evaporate due to its unstable molecular structure.”

This change in flavor is often just a muting of the original taste, but oxidation over time can sometimes give bitters a metallic, iron-like taste. This phenomenon hinges upon the level of water and organic matter in the bitters in question. For instance, Fee Brothers uses fresh ingredients like fruit extracts and almond oil in their bitters. This makes them taste great, but consequently, their flavor fades rather quickly. Fee Brothers’ bitters also have a generally high water content, which contributes to a faster rate of oxidation. “It’s akin to opening a bottle of vermouth — both have about a one-month shelf life in the fridge,” says Adler.

Fortunately, most bitters have enough alcohol or glycerin in them to prevent perishability from becoming a major threat. Regardless, the best way to keep your bitters fresh, and to slow down any oxidation, is to store them in the fridge. If you feel so inclined, jot down the date you bought your bitters on their bottles to keep track of their ages. Ultimately, they won’t last forever, but you won’t get food poisoning from them, either.