The good folks at Dogfish Head Craft Brewery—by any measure one of the more interesting and accomplished breweries around—have done us a disservice. They recently brewed up an IPA called “Hoo Lawd” (say it out loud), which they claim is the “hoppiest beer ever.”

While the average IPA lands somewhere between 40-60 IBUs, this latest release clocks in at 658 IBUs (international bittering units)….  While other awesome, uber hoppy beers have claimed to achieve higher theoretical IBUs, Hoo Lawd has received scientific confirmation and documentation from two independent labs that this is, in fact, the hoppiest commercial beer ever brewed.

The disservice in this case is not the beer (which I haven’t tasted and which may be sublime), but the use of IBUs to stand in for a measure of “hoppiness.” This acronym appears almost as frequently on bottles and chalkboards as “ABV,” but it’s at best irrelevant and at worst misleading—because IBUs don’t measure “hoppiness,” they measure bitterness.

The cone (or “strobile”) from the common hop plant may look unimposing, but it contains hundreds of chemical compounds, and these compounds do quite a bit to alter a batch beer. Their most important function—the reason they are in nearly every beer made—was originally their anti-microbial qualities, which warded off spoilage and made beer last longer. Other compounds help build a rich, stable head and make it easier to create the beautiful tracery left behind on the glass. Breweries started adding spices to beers almost immediately after learning to brew them, in part to balance the sweetness of the malted grains and hops turned out to especially able in this regard, too.

But perhaps the most important function of hops in modern brewing is to impart the distinctive flavors and aromas that infuse 21st century beers. They’re incredibly versatile, expressing themselves as fruit (mango, lychee, apple), forest (pine and cedar), wine (usually white wine grapes), flowers (geranium, rose, gardenia), and of course citrus (orange, lemon, grapefruit). When you encounter a saturated American IPA, you’re getting a full-frontal assault of these flavors and aromas. It’s what characterizes these beers, and why they are becoming so popular. But IBUs, which express the amount of certain dissolved compounds in solution, only measure bitterness.

This distinction between flavor/aroma and bitterness is far from academic. Modern brewing trends, especially in the U.S., are geared toward amping up hop flavors and aromas. We’ve seen an explosion in hop breeding programs where the express goal is to get ever more expressive hops. It’s true not just in America, but Germany, England, New Zealand and Australia. The beer styles that take advantage of these qualities have seen a similar spike in popularity. IPA is now the most popular style in the craft segment in the U.S., tripling in popularity from just seven years ago. The whole reason breweries started citing levels of IBUs in the first place was to draw attention to the hops.

What’s fascinating is that brewing processes have shifted enormously in the past decade, as breweries try to wring ever more flavor and aroma out of the hop—and that has in turn further exposed the inadequacy of “IBU” to capture all the dimensions of “hoppiness.” Until fairly recently, breweries made hoppy beers the way they always had, by dosing their batches with a heavy load of hops early in the boil. Heat slowly converts one compound, alpha acid, into iso-alpha acid, the main compound responsible for bitterness. But hops that stew in boiling wort for 60 or 90 minutes lose most of the flavor and aroma compounds, which come from delicate, volatile essential oils. Breweries would throw in a few more toward the end of the boil to make sure they got some aroma and flavor, and they might have dosed the fermented beer as it sat in a conditioning tank (called dry-hopping) to add more. But the bulk of the hops went in at the start of the process.

Now breweries are starting to flip the equation. Instead of putting most of the hops in at the start of the boil, they put most in at the end—or even after the boil. Indeed, it is very common for breweries to use massive doses “post-boil”—hops that go into the wort after it’s taken off the flame. Much like steeping tea, this wort becomes infused with those delicate oils and terpenes and other aroma compounds, and develops that intense flavor we now associate with IPAs.

If you happen to have an IPA in your hand, put your nose over the lip of the glass. (If not, imagine you have one nearby.) What makes these beers so beguiling is that blast of aroma rising up. When you sip the beer, the flavors are just as vivid, like juice taken directly from tropical fruits.  It’s possible to have an extremely bitter beer that has almost no aroma and little hop flavor; it’s also possible—and now common—to have a beer that is absolutely packed with flavor and aroma but is not very bitter. I have on more than one occasion overheard someone tell a bartender: “I don’t really like bitterness; what I like are IPAs.” This is not an uniformed patron; it’s a patron who lacks the language to express what he likes about a beer. He’s actually pointing out one element of “hoppiness” that isn’t captured by IBUs.

For you visual thinkers out there, here’s the way we currently try to express “hoppiness.”

Mistaken View of Hoppiness

Here’s how we should express it:

A Complete View of Hoppiness

Hoppiness is not bitterness alone, and it can’t be expressed by IBUs alone. Hoppiness is that delightful mélange of bitterness plus aroma plus flavor. We may be a long way from being able to express that in a simple number, but we need to at least be thinking of it in these terms.

Jeff Alworth is the author of the book, The Beer Bible (Workman, 2015). Follow him on Twitter or find him at his blog, Beervana.