The story of how beer gets its bitter (as well as its brown bottle) comes down to a bit of chemistry and three mysterious little letters. Short for International Bittering Units, IBU is a brewing acronym that is as ubiquitous as it is puzzling. That’s why we asked Dave Bergen, director of brewing at Edgewater’s Joyride Brewing Company—which celebrated its eighth anniversary in July—to help break down what IBUs are, as well as what they aren’t.

Bergen has been professionally brewing for over eight years, and founding a brewery that dabbles in a bounty of beer styles means he knows IBUs like the back of his hand. In basic terms: Hops are the source of beer’s bitter taste. Raw hop cones contain alpha acids, a class of chemical compounds that themselves are not very bitter, according to Bergen. However, when heat is applied during the brewing process, these acids isomerize—a process which changes their physical structure but maintains their elemental composition. The resulting iso-alpha acids are much more bitter, and these are measured on the IBU scale. One IBU is roughly one milligram of iso-alpha acids per liter of beer.

Dave Bergen of Joyride (right) and David Warren of High Wire Hops (center)
Dave Bergen of Joyride (right) and David Warren of High Wire Hops (center). Photo courtesy of Joyride Brewing Company

Bergen emphasizes that a beer with a high IBU value is not necessarily an indication of intense hop flavor, which is a common misconception. While IBU increases as hops boil for longer, volatile essential oils carrying the hops’ piney, citrusy flavors get swept away in the steam. This zero-sum game between bitterness and aroma means that brewers add different hops at different stages of the beer-making process. High-alpha-acid bittering hops are usually added early during the boil, while hops prized for their aroma are usually added during or after cooling. A technique Joyride uses for pale ales is hopping at the “whirlpool” phase, a stage right after boiling in which the brew is spun to remove sediment. This, as Bergen says, hits the sweet spot with some isomerization while retaining most of the essential oils that give hop-forward beers their fruity, floral, and spicy notes.

Historically the IBU scale ranged from 0 to 100. “Science suggests that we really can’t detect anything more than 100,” Bergen says, “and that it’s also really hard to get that amount of bitterness dissolved into a liquid.” Joyride likes to run the gamut in its taproom, bottoming out at an IBU value of 5 to 10 with its lagers, climbing up with kölsches and saisons, and hitting its max with the 70-IBU double IPA.

While beers today can sometimes reach up to a 120 IBU value, Bergen says the heyday of this style is over. The “IBU wars”—a period starting in the ’90s when IPA-heavy breweries tried to out-bitter their competitors to extreme lengths—was originally a reaction to the cultural dominance of low-IBU, light American lagers. The face-furrowing results perhaps went too far, though, ushering in a trend in the past five years of vast beer debittering, which Bergen says likely overlapped with the rise of the easy-drinking hazy IPA. By providing a range of beers with different levels of IBUs, a lot of breweries let customers choose where they want to fall on the spectrum.

For folks drinking at home, the IBU isn’t just a unit of bitterness, though. It also offers a reminder to store your beers properly. Ever wonder why beer bottles are so often dark brown? Brewers in the early 20th century discovered that darker glass prolonged a beer’s freshness and prevented it from turning, for lack of a better term, “skunky.” According to modern research, it’s the same iso-alpha acids of IBU that cause this odor, decomposing into those “skunk” compounds when exposed to light. Protectants have been developed to allow even clear-bottled beer to keep, but they nor colored glass are a total fix. To be safe, stick your brews in the fridge.

Regardless of where you’re drinking, Bergen suggests using the IBU scale as a general guide rather than a black-or-white indicator of a beer’s bitterness. A milk stout, for instance, might have the same IBU value as an IPA, but its bitterness will be masked by the sweet lactose and roasted malt flavors. Especially at smaller breweries like Joyride, batch to batch variability also impacts the bitterness of a given pint.

Joyride stopped displaying beers’ IBUs on its chalkboard menus two years ago because of confusion around the scale’s meaning, but if you want to exercise your newfound knowledge, the team is more than happy to explain all the numbers they have on tap. It’s like accounting, in a way, because bitterness is there to make sure a brew is completely in balance. “Otherwise,” Bergen says, “beer is just sugar juice.”

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Ethan Pan
Ethan Pan
Ethan Pan is 5280’s associate food editor, writing and editing for the print magazine and Follow his dining/cooking Instagram @ethans_pan.