From Vol. 2, No. 11, March 2018
The International Bitterness Unit is not irrelevant. Excuse the double negative, but it does not seem enough these days to simply state the IBU is relevant. No, it does not accurately reflect the perceived bitterness of a New England IPA, or many other late-hopped beers. However, it remains a useful tool for brewers, one that makes it easier to produce consistent beers across numerous styles.
Aaron Justus, director of research and development and specialty brewing at Ballast Point Brewing, recently discussed how that brewery has tracked IBU through the brewing process. He presented the information at Brewing Summit 2018 and also summarized it in the Maser Brewers Association of the Americas Technical Quarterly (Vol. 55, no. 3). The podcast is open to anyone who wants to listen, but TQ access is limited to MBAA members. Here are the highlights:
– Utilization for mash hops was 9.1%. Utilization was 44% during a 60-minute boil and 29.9% in the whirlpool. Most of the research was conducted in Ballast Point’s 50-barrel brewhouse, although some on its 5-barrel system and some on its 150-barrel system. That’s considerably better than a brewer would expect on a small system, particularly one producing 5 or 10 gallons at a time. But the takeaway here is that whirlpool hopping is much more efficient than brewers realized in the past.
– The majority of IBUs are gained in the first 5 to 10 minutes of boiling or the first 5 to 10 minutes in the whirlpool. For instance, utilization reached 58% in a 13.8°P Scottish ale in five minutes, and 64% in 60 minutes. Utilization in a higher gravity (20.2°P) imperial red was 17.5% after 10 minutes and 20% after 60 minutes.
– A higher hopping rate and a higher gravity both reduce utilization. For instance, utilization for a 13°P blond ale hopped with 0.13 pounds per barrel was 45.3%, while one hopped with 1.18 pounds per barrel was 30.6%.
– Total loss of IBU during fermentation and filtration was about 33%. Most of that came in the first two days of fermentation, and 5 to 10% during centrifuging and filtering.
– All else being equal, beers that rely on whirlpool hops for bitterness lose more IBUs during fermentation.
– Using low-flocculant yeast results in more IBU loss than fermenting with high-flocculant yeast.
Justus has created predictive equations for both hot-side utilization and whirlpool utilization. These are both in his Technical Quarterly paper. His disclaimer is worth repeating: “I want to emphasize that every brewery is unique and these equations are not universal.”