Yes, Dry-Hopping DOES Add Bitterness to Beer

You'd think someone who has been writing about beer for 20 years would have a pretty good handle on something as basic as hop bitterness. The past few months have caused me to rethink this hypothesis. The reason for this is not unique to me, though: it's a function of the modern habit breweries have of adding unprecedented levels of hop matter to their whirlpools and conditioning tanks.  What I have to offer you today is a Jackson Pollack-like spatter post of data points that do not provide answers, but do, perhaps, begin to define the questions.

Let's start with a sensory experience. On Saturday night I visited Great Notion here in Portland, a brewery self-consciously designed to produce "New England-style IPAs." I had a glass of Juice Jr. (pictured above) and Mandela, and somewhere near the end of the first glass, I had a slight epiphany. These beers are made to accentuate fruitiness, both of the yeast but especially hops, and downplay the bitterness. To my palate, however, they are limned with an unusual and harsh bitterness unlike the kind isomerized alpha acids produce when they're boiled in the normal brewing process.

It's not just Great Notion. I recently made one of these beers myself using a yeast strain (Dry Hop) engineered by Imperial Labs for the purpose, along with lupulin powder. It had that same unpleasant bitterness. Recently, a New Englander sent me a can of Trillium's pale ale and I found it harshly bitter, too. Even after the first two instances, I didn't start connecting these dots. But when Juice Jr. hit my palate that way, I started rethinking things. What's that bitter note I'm detecting that others are not? Where does it come from? Am I the only one tasting it? Well, let's dig into what we know.

American hoppy ales are weird beasts that behave differently than the brewing books suggest. No brewing tradition has ever leaned as heavily on the sheer volume of hops that go into these beers very late in the boil, post-boil, and especially, in the fermenting or conditioning beer as dry-hopping.

So if you think of a typical beer ten or twenty years ago the hopping—even if you think about Jever [a German pilsner], which is a hoppy beer—the hopping level, which is just a front-end kettle hop addition, compared to a beer that’s kettle hopped, whirlpool hopped, and dry hopped, you might have twenty to forty times more hops being used in those beers than a traditional lager beer.
— OSU hop researcher Tom Shellhammer

What happens when you add forty times as much hops to a beer? Tom explains that "BUs--and the sensory bitterness--is creeping up in dry-hopping or late-kettle hopping or whirlpool hopping for a number of reasons." And "the most significant reason is that there are oxidation products in hops." These are called humulinones, and they look almost identical chemically to the iso-alpha acids that produce bitterness the normal way. We've known about them since the 1950s, but they were at most a curiosity--no one was extracting them in concentrations high enough to move the needle on a beer's bitterness. Until now.

Last year, SS Steiner published an absolutely amazing study on humulinones. Stan Hieronymus actually blogged about it, but I think my brain, unable to absorb the information, dumped the memory file. They behave very oddly, affecting not just bitterness, but pH and iso-alpha acids. I'd strongly recommend reading the article and Stan's piece, but here are the key findings:

  • Humulinones can create about two-thirds as much bitterness as iso-alpha acids, but are beer-soluble and are absorbed fairly quickly during dry-hopping.
  • When researchers used greater loads during dry-hopping, they reduced the concentration of iso-alpha acids in the beer. That's right, bitterness from humulinones reduce bitterness from alpha acids.
  • Dry-hopping raises pH. From the report: "The results showed that regardless of the beers’ starting IBU or pH, dry-hopping had a linear impact on pH, with the pH rising by about 0.14 pH units per pound of hop pellets dosed."
  • Pellets have more humilonones than whole-flower hops because the lupululin glands are broken. This happens even when pellets are vacuum-sealed and packed cold.

In an email exchange, Stan sent along this slide to illustrate the interaction between iso-alpha acids and humulinones. It comes from a presentation at the most recent CBC by Steiner's technical director, John Maye.

Finally, and to me, most confusingly, those Steiner researchers described the humulinone bitterness as smoother. “ The bitterness profile of the humulinone beer, however, appeared smoother, and there was less lingering on the tongue than with the iso-alpha acid beer. This smooth bitterness makes sense given humulinones are more polar than iso-alpha acids and should therefore not stick or linger on the tongue as long as iso-alpha acids.”

Wait, smoother? Either they don't taste smoother to me, or there's another cause. Well, there are other causes. Again, when we're dealing with such extravagant amounts of hopping, even tiny contributors may play a noticeable role. Which ones? "Polyphenols as well to some degree," Shellhammer noted. Polyphenols are a bit like tannins, and by Tom's description, these seem more likely to be the cause of the objectionable bitterness I taste. "Like when you make tea at home, you can get bitterness from that. When they're really small they can taste a bit more astringent." 

Another possibility is beta acids, another constituent of hop oil. They seem important--though to my knowledge unexplored. Just as oxidized alpha acids become humulinones, oxidized beta acids become transformed as well--into hulupones. Again, our friend Tom Shellhammer elaborates at Beer and Brewing Magazine.

However, hulupones are bitter and can contribute substantially to the final flavor of beer. Anecdotal claims suggest that hulupones have an unpleasant bitterness quality. Hulupones are relatively stable once formed and can survive all stages of the brewing process. They can be formed via the oxidative degradation of hops during storage. As hops oxidize, the bitterness that comes from iso-alpha acids diminishes because their precursors, alpha acids, are lost as a result of oxidation, but this is somewhat offset by the presence of bitterness from the hulupones.

There are a couple other things I'll throw into the mix. First, all of this illustrates that chemical interactions are moving variables around, so we need to be wary of fixed points. What else is moving the dials? We know for sure that yeast creates "biotransformation" of hop flavors; what else is it doing? Another question I keep coming back to has to do with human hardware. We know we don't all get the same flavors from hops; you may get lemon or dill from Sorachi Ace, white wine or human sweat from Nelson Sauvin. When someone tastes humulinone bitterness and gets a "smoother" quality, is that a universal experience, or will each person get different levels of smoothness?

In our exchange, Stan added glycosides as another factor that might affect bitterness. Of course, hop variety, dry-hop method, and any number of other untested variables may well be at play. And these are the known-knowns. What else may be happening that we haven't discovered yet?

What we're left with, at this moment, is a fascinating stack of questions to which answers will be very slow in coming. The one answer we can definitively provide is this: that old myth that dry-hopping doesn't add bitterness is not strictly true. In high enough volumes, dry hopping is a significant source of bitterness. (Forget those "zero IBU IPAs.") What the precise sources of that bitterness are and how breweries can control it remain very open questions. Going back to that glass of Great Notion Juice Jr. I was drinking, I have a few possible suspects that might account for the harsh bitterness I tasted (including user hardware), but no convictions. And it will almost certainly be awhile. I am, however, looking forward to the field work.