The international bittering unit (IBU) is meant to tell us something about the bitterness of our beer, but the scale is far from perfect. What does it mean for two beers to express the same bitterness, and must numerical equality necessarily follow sensory equality? Here are two perspectives on bitterness and IBUs from experienced homebrewers who have spent more time than most of us pondering such ideas.
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The Hop Paradox: Are Homebrewers Getting IBUs All Wrong?
By Kyle Jones
Something has been bothering me lately. It started with an ongoing problem with some of my hop-forward beers: many didn’t have quite the level of bitterness I had targeted. I was pretty confident in my homegrown brewing software, which is based on data in classic books by Greg Noonan, Ray Daniels, and others, as well as on the most current scientific data available to me. It uses the Tinseth method to calculate hop utilization with an integral calculus approach that accounts for the increase in wort gravity as the boil progresses.
I had long suspected that estimating the final bitterness of a homebrewed beer is one of the more imprecise things we do during recipe formulation. I had also been toying for some time with a method to empirically determine how much “effective utilization” one gets from a first wort hop (FWH) addition, considering both the purported “smoother” bitterness and the fact that some alpha acids are isomerized before formation of the hot break.
Iso-alpha acids that form before the hot break may precipitate out as proteins denature, coagulate, and form the break material. It’s also likely that hot break protein complexes are generally larger than the cold break complexes that form after vigorous boiling fragments the proteins that remain after the hot break.
Neither forums nor textbooks have much to say on the subject. Eric Warner, in his fantastic tome German Wheat Beer, discusses in the glossary (p. 139) that the formula he presents for estimating international bittering units (IBUs) can “be off by as much as 20%” owing to iso-alpha acid precipitation during fermentation and aging. In his excellent For the Love of Hops, Stan Hieronymus goes further, discussing work by Tom Nielsen at Sierra Nevada that indicates an IBU loss of approximately 20 percent during fermentation.
Hieronymus also cites observations by Mitch Steele, formerly of Stone Brewing, that suggest wort-to-bottle IBU losses of approximately 23 percent. Steele attributes these losses in part to pH drop during fermentation, which reduces the solubility of isomerized alpha acids. Hieronymus concludes that brewers can expect “about 50 percent of iso-alpha acids will be lost in the brewhouse and another 20 percent during fermentation and packaging” (p. 190-191, emphasis mine).
What really confuses me, though, is that homebrewing texts and recipes don’t seem to account for this phenomenon. Take, for example, the Ballast Point Grapefruit Sculpin clone recipe that appears in Zymurgy’s 14th Annual Best Beers in America survey (July/August 2016). The formulation specifies 70 IBUs, which is the exact same value listed on Ballast Point’s website.
I wondered, “How can a clone recipe that targets a certain wort bitterness have the same IBUs as the real deal, for which bitterness is presumably measured in the finished beer?” Ballast Point confirmed that those 70 IBUs are, indeed, measured in the finished beer and also stated that the brewery does account for IBU loss during fermentation and packaging. So some breweries adjust for this.
But others don’t. The Boulevard Tank 7 clone recipe appearing in the same issue specifies 37 IBUs, which the published hop additions do provide in the wort. Boulevard’s Tank 7 web page places the beer at a negligibly different 38 IBUs, and like Ballast Point, the brewery confirmed that this is measured in the finished beer. However, the hop schedule for Tank 7 that Boulevard graciously provided to me works out to about 38 IBUs going into the wort, suggesting zero bitterness loss from kettle to bottle.
To further complicate matters, a local brewery in Texas reported that they account for iso-alpha acid losses approaching 50% for some of their beers. That three breweries account for IBU losses so differently may reflect differences in how beer is produced, including differences in brewing systems, wort production methods, yeast flocculation, and clarification methods (e.g., centrifuged only vs. centrifuged and filtered).
Cloning commercial recipes is especially difficult when it comes to IBUs, as commercial breweries boil much larger volumes than do homebrewers, and wort runoff after the whirlpool takes much longer at commercial scales, meaning utilization for late and whirlpool hop additions is probably higher in commercial breweries than in home breweries. Test batches help brewers predict final IBUs they can expect from the hops they add to wort, but even commercial breweries find it difficult to translate IBUs from pilot-scale brews to full brew lengths.
These differences aren’t just limited to commercial clone recipes. In several Brewers Publications titles that feature recipes from well-known brewers, specified wort IBU levels, backed up by the weight, timing, and type of hop additions, typically fall squarely within the IBU ranges specified in the 2015 version of the BJCP Style Guidelines. For moderately hopped beers with relatively well-defined IBU ranges, such as German Pilsner and California Common, we might expect that targeting stylistically middle-range bitterness in the wort would yield finished IBUs nearer the low end of the style range, assuming even a 25 percent loss of IBUs from the kettle through fermentation.
It is important to note this assumes that IBU levels reported by the BJCP correspond to bitterness in the finished beer, which is how I suspect most brewers interpret them, although this is not explicitly stated in the Style Guidelines. The same pattern is present in many recipes from National Homebrew Competition winners in the September/October 2015 issue of Zymurgy.
Of course, all this said, myriad factors affect perceived and measured bitterness, many of which have nothing to do with iso-alpha acids at all. And in fact, homebrewers face much uncertainty in even estimating IBUs in wort or finished beer—utilization formulas, concentration corrections for wort gravity and iso-alpha acid content, first-wort hopping, and alpha acid losses during hops storage, to name just a few. Comparing bitterness in a finished beer to predicted IBUs for different homebrewed beers might be a great undertaking for a future AHA Fund Research Project. But even measurement of IBUs is fraught with uncertainty, and there are several anecdotes of different labs reporting vastly different measurements of IBUs in finished beer.
So, in the end, what does all of this mean? To me, it means that—based on my observations about the beers I brew—I probably need to increase the target IBUs in my own system by 20 to 40 percent to account for losses in the kettle and during fermentation. Perhaps I can become slightly more sophisticated by also accounting for yeast pitching rate in the future, as it is well-known that iso-alpha acids (and other hop compounds) bind to yeast cell membranes and are removed from the beer when yeast flocculates. Who knows? We might even see yeast strain data sheets updated to include information on expected iso-alpha acid losses at recommended pitch rates, as even different yeast strains vary in their propensity to bind these compounds.
To others it might mean not agonizing over whether to use the Rager, Garetz, or Tinseth formula, or whether to apply a 10-percent versus a 15-percent correction for alpha acid loss during storage. It also might that you don’t hit the target the first time out when trying to clone a commercial beer, as matching a commercial beer IBU-for-IBU is, in most cases, unlikely to yield a beer with the same perceived bitterness. Calibrating your palate and adjusting your hop additions based on your perception of bitterness in a fresh example of the beer you are trying to clone may be the best approach. Certainly perception of bitterness quality plays a role as well, and “smooth” bitterness may be confused with less bitterness.
But without a doubt, the most interesting thing will be debating this over a few IPAs at the next Homebrew Con.
Kyle Jones is a BJCP National-ranked judge and a member of the Houston Foam Rangers homebrew club. He lives in Bellaire, Texas. Kyle wishes to thank Eric Warner, head brewer at Karbach Brewing Company in Houston, and Scott Birdwell, owner of DeFalco’s Homebrew Supply, also in Houston, for their helpful discussions on this topic.
Of Systems and Perception: Why Targeting Bitterness is so Elusive
By Amahl Turczyn
As I’ve mentioned in previous articles, I prefer to first-wort hop most of my lagers, and I suffer IBU losses accordingly due to the binding of alpha acids with break material. My solution is to increase first-wort hop additions by about 50 percent on when I brew at home. But differences in equipment as well as procedure can also affect utilization.
For example, such increases were not necessary in the 10- and 7-barrel brewhouses I’ve brewed on, but we brewed mostly ales on those systems and never added first-wort hops. All of our hops were added post-break. This resulted in a relatively harsher bitterness, but it was desirable for the styles we made, and fewer hops were necessary to achieve the same IBUs. For craft brewers, cost of materials is always an issue. At home, I don’t mind buying twice as much Magnum to bitter my Classic American and Bohemian Pilsners.
I don’t see such compensation as a paradox as much as a reflection of just how different everyone’s systems are. When I brew a recipe from a magazine on my home system, clone or otherwise, I know I have to factor in a significant increase for bittering additions to get the same bitterness that was intended. Even post-break, 60-minute additions need a 20-percent boost.
Beyond that, there are dozens of other factors that affect isomerization. My home brewery doesn’t reach the full, crashing boil that Oasis Brewery’s kettle did, but then again, neither did the kettle at Wolf Tongue Brewery. Wolf Tongue was more than 8,300 feet (2,530 meters) above sea level—and since water (and wort) boiled at about 196° F (92° C), that also affected isomerization, but only by a small amount. The biggest problem was the electric heating elements we used, which could only manage an enthusiastic simmer. So we added more hops to compensate.
You get a feel for the level of bitterness you can expect from certain alpha additions on certain systems and plan accordingly. That isn’t a very scientific assessment, but as Kyle points out, even testing for bitterness levels can have a margin of error from lab to lab. And that testing is expensive, often prohibitively so for the small brewer.
And then there’s the issue of actual IBUs versus perceived bitterness. A caramel-heavy, under-attenuated English barleywine or double IPA might contain 100 calculated IBUs and still taste much sweeter than a dry, West Coast-style “single” IPA that boasts just 70. Most brewing software calculates dry hop additions to contribute 0 IBUs, but anecdotally, those resinous hop oils do contribute to the sensation of bitterness as well as to hop flavor and aroma.
It’s also very possible that just as some beer judges are more sensitive to off-flavors like diacetyl, clove phenols, or metallic character, they might also have differences in sensitivity to the perception of hop compounds. The type of hop compounds also matters: I find that Calypso and Horizon have very smooth bitterness for high-alpha hops, whereas Comet and Chinook are harsher and more astringent. This may have to do with cohumulone levels, but there are many more compounds that could affect smooth or harsh perception.
Perception of hop character, when drinking a beer, involves myriad olfactory transmissions from palate to brain. (See Kevin Wright’s piece on Sensory Analysis in the July/August 2016 issue of Zymurgy.) It would be great to quantify them in a lab, and I imagine big brewers spend a lot of capital attempting to do just that. But for small and amateur brewers, measuring exactly how hoppy any given beer isn’t strictly necessary—it’s enough to recognize relative hop intensity from one beer to the next. I’ve had a lot of 70-IBU IPAs from many different craft breweries, and perceived hop bitterness is seldom the same.
Given the unavoidable differences from one system to the next, all we can do for recipes in Zymurgy is choose an “average” system’s utilization, keep parameters like batch size and efficiency consistent, and let homebrewers tweak them as necessary. For the clone recipes that I’ve developed for Zymurgy, I go by the numbers predicted in BeerSmith 2. Since you can choose the calculation formula, I stick with Tinseth. Plugging the same recipe into other brewing software may yield different numbers, but from what we’ve seen, they’re usually fairly close.
As homebrewers, one of the fun things about brewing is making a batch from a recipe, evaluating it, tweaking it to our individual tastes, and then brewing it again. Craft brewers do this, too, at least during the initial stages of releasing a new beer. They brew a pilot batch—or maybe more than one—and once they get the recipe dialed in, especially if they are going to add that beer to their regular lineup, they keep the recipe as consistent as possible.
I still find it amazing that craft brewers can take a homebrew recipe for the Great American Beer Festival (GABF) Pro-Am competition and spin it up to seven or ten barrels of (hopefully) identical beer without necessarily knowing what the original homebrewer’s system was like. There’s a substantial margin of error there that they must overcome in the process, and getting it right usually comes down to experience.
Amahl Turczyn is associate editor of Zymurgy. He homebrews in Lafayette, Colo.
The post Bitter Debate: Two Perspectives on Achieving Consistent Bitterness in Homebrewed Beer appeared first on American Homebrewers Association.
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