The Age of Hops, IBU Edition
Two of the most common axioms used to describe brewing hold that “pilsner is the hardest style to make because there’s nowhere to hide” and “IPAs are easy because all you have to do is throw in a lot of hops.” Both are wrong, but the latter is probably wronger. While it is true that “throwing a lot of hops” in a beer will create some kind of IPA, doing so without understanding the incredible complexity hop variety, technique, and chemistry exercise on the operation is bound to result in a bad IPA. Making any beer badly is easy. Making any beer consistently very well is harder. Good IPAs are especially hard because of all the variables at play.
For years now I’ve meant to catalogue some of the complexities. There is a free and public source for extremely technical and nerdy subjects, and one brewers, pro and home alike, should access: the Master Brewers (MBAA) Podcast. While some of it is so technical and specific to the industry, you can skip around (a show about stainless steel passivation, for example), some is essential listening even for non-brewers. Much involves current research that answers riddles, contradicts romantic facts, or unearths entirely new information. One of the richest veins involves study into the way hops behave when you use them the way Americans have over the past decade. So much of their behavior in the IPA mode is either unprecedented or done so weirdly it is entirely new or contradicts earlier research. It’s incredibly rich stuff. To kick things off we turn to the way hops create bitterness in different conditions, from research by Ballast Point’s Aaron Justus.
Justus conducted research at Ballast Point’s three breweries, but most of the data came from their 150-barrel brewhouse. His research investigated what processes and conditions affected hop utilization (the creation of bitterness) across fourteen types of beer and all phases of the brewing process. His discoveries were not uniform across all systems and this is a big part of the findings: if you’re brewing on a 5-gallon system at home, the results may not be the same as they were in his 150-barrel commercial brewery. For a number of reasons, the bigger systems got higher utilizations than the small (5-barrel) direct-fired brewery. Still, while the exact BU figures may vary, the lessons are highly instructive.
In short, a huge amount of the working assumptions about hop utilization really don’t track when you’re making beers with five pounds of hops per barrel, or extensive use of hops in whirlpools and on the cold side—practices unknown to brewers even a decade ago.
Mash and Kettle Hops
Mash hops were a thing a decade and more ago, but they haven’t been the focus of brewing for awhile. Nevertheless, Justus investigated them and made some interesting discoveries. In particular:
Mash hops have a sensory impact, though it’s subtle.
More interestingly, they contribute IBUs. He found that a half pound per barrel of high alpha hops will contribute 20-30 IBUs, and pegged utilization at 8-10%.
Furthermore, there’s a leveling out of all additions over the course of the boil, so if you only use mash hops, they will contribute more IBUs than if you have many additions. They don’t just stack cumulatively. He isn’t sure of the mechanism but wonders if thermal degradation (the breakdown over the entire process of mash, boil, and whirlpool) plays a role.
Kettle Hopping
Justus offered two big findings from their research on kettle hops, one expected, one not. He was surprised to find that the vast majority of bitterness came in the first five minutes of the boil. This contradicts all the research I’ve seen, in which the bittering curve takes a lot longer to develop. (In the kettle, the bitterness comes from the conversion of alpha acids into iso-alpha acids.)
He didn’t speculate on the reason for the discrepancy (higher-alpha hops?), but it conforms to the observations many other American brewers made when they were trying to build juicy beers and kept finding their kettle additions were adding too much bitterness. It was true of additions made at different points in the boil as well. Thirty- and ten-minute additions “behaved very similarly to 60-minute additions.” In his research, he found that after five minutes, you’ll only pick up another 5-10% more utilization. (That’s not nuthin’, given that utilization won’t go much above 50%, but it’s striking nonetheless.)
However, other factors scramble the potential for utilization. “If you’re doing a Scottish ale where you’re hopping at .1 pounds per barrel, you’re going to get about 60% utilization, whereas if you’re doing an imperial red which is super-high gravity and the hop rate is outrageous, your utilization is going to drop below 20%.”
Additionally, the alpha content of the hop affects utilization. They compared the effect by kettle hopping a blond ale with .1 pounds per barrel of Polaris (super high bittering potential, ~21%) and the same beer with 1.2 pounds per barrel of Tettnanger (low bittering potential, ~4% alpha). He got 45% utilization from the Polaris and only 30% from the Tettnanger.
Whirlpool and Dry Hopping
Although brewers have known this for the better part of a decade, adding hops to the whirlpool adds quite a bit of bitterness. In the various beers he studied, Justus measured utilization at 20-44%. That range is affected by the wort more than the conditions. Time isn’t a big factor. Most of the pick-up happens within ten minutes and then very little afterward. Given that in commercial breweries this step takes a lot longer than 10 minutes, time is irrelevant—though homebrewers should take note. The biggest effect is hop rate—the more hops you use, the lower the utilization. Additionally, the closer you are to saturation (around 100 IBUs), the lower the utilization. In other words, adding a modest amount of hopos to unhopped wort will result in the greatest utilization. Adding a lot of hops to already-bitter wort will result in the lowest utilization. Gravity also affects utilization, but Justus found that effect only really started after 13° Plato (1.053).
Fermentation and Dry-Hopping
Once fermentation starts, a third of the existing bitterness will vanish during fermentation (34% on average in Justus’ sample), most of it in the first day or two. That figure isn’t static: the type of yeast and gravity also affect loss. Low-flocculation yeasts (those that stay in suspension) scrub more IBUs than those that drop out more quickly. Higher-gravity worts, which cause more vigorous and longer fermentations, also suffer greater IBU loss. This suggests that whatever causes yeast to remain present and active in the wort longer will cause it to scrub more bitterness from the wort during fermentation.
Curiously, the IBU loss was bigger for beers with high whirlpool additions. That means that if you’re relying on whirlpool hops for bitterness, you’re going to lose more of them during fermentation. Finally, even centrifuging the finished beer doesn’t lower the bitterness tremendously. However, when he used both a centrifuge and a filter, the bitterness dropped another 15%.
Dry-Hopping and Increasing Bitterness
Of course, dry-hopping can create IBUs, so there’s an exchange happening in dry-hopped beers. The mechanism isn’t the same. The bitterness extracted during dry-hopping doesn’t come from iso-alpha acids, since there’s no heat for conversion, but rather humulinones (and possibly polyphenols). This accounts for what some people (but not all!) characterize as “soft” bitterness—a quality Justus identified. So how’s that all working? He looked specifically at several modern hazy IPAs they make.
In beers with two additions (initial charge 1-2 after start of fermentation, second at the end of fermentation), he was finding amazing increases in measured bitterness typically in the 20-30 IBU-range. “We’ve even done beers now where we dry-hop only at terminal gravity, 3-4 pounds per barrel, and we’ve seen an increase of 30-40 IBUs.”
In two different session hazies where hops were only added on the cold side (dry-hopped), they picked up 25 and 40 IBUs. “It really depends on what hops you’re using.” Justus speculates that higher-alpha hops have higher humulinone amounts, so the pick-up is greater.
Finally, he also found, and was amused by, the way hot-side hops reduced haze stability (that is, made them clearer), a downside for some breweries looking to amp the haze.
Takeaways
This post focuses entirely on bitterness, not flavor and aroma. Even so, there are tons of levers to pull when you’re trying to address bitterness. Some of them will cancel each other out. Others will work in tandem but contribute different kinds of bitterness. Just isolating this one dimension reveals all the factors brewers have to keep in mind at every stage of the process in order to arrive at a level and type of bitterness they desire.
It also illustrates how far we’ve come in such a short time. When brewers were first turning to whirlpool and dry-hopping for the majority of their hop additions, they were under the assumption, unchallenged for centuries, that they weren’t contributing much or any bitterness. For a period around the mid-teens, breweries touted “zero IBU IPAs” because they believed beers made without kettle hops couldn’t be bitter. In that short period of time we’ve learned a great deal, and Justus gives us much more to consider.
For commercial brewers, there are many lessons that may save time and money—though that picture is complicated when the flavor and aroma dimensions are included in the picture. Just being aware of the different causes may make brewers choose differently. At one point in the discussion Justus asked, “If almost all the utilization happens early in the boil, why not just do 15 minute additions?”—a question he didn’t answer himself. But looking at his findings, you may ask the same question. We’ve entered this new age of hops, and the lessons—and questions—are coming fast.
And, to conclude where we started, let’s return to that comment about “easy.” As you can see, there’s nothing easy about trying to compose a recipe and formulation that nails the level of bitterness a brewer wants. “Throwing a bunch of hops at it” will have many unintended (and previously misunderstood) consequences.