Recent research related to hops and brewing is not making life easier for the people who write brewing software.
Exhibit A: A peer-reviewed paper in the Master Brewers Association of the Americas Technical Quarterly titled, “Humulinone Formation in Hops and Hop Pellets and its implications for Dry Hopped Beers.” (A condensed version of the results of the S.S. Steiner experiments described in the Technical Quarterly is available at the Hopsteiner website.)
Exhibit B: Research going on at Urban Chestnut Brewing in St. Louis related to the impact of dry hopping on pH, then the impact of pH on perceived bitternes.
We’re not talking about changes in International Bitterness Units (IBU) that result from dry hopping, so I pretty much made up that part about problems for brewing software. But the changes in bitterness are real. So ripped from the headlines:
– Humulinones are formed by the oxidation of alpha acids within the hop. They are not a recent discovery, but there was little reason to pay attention to them before brewers began dry hopping at the rate some do today. Yes, you may blame IPAs.
– They are about two-thirds as bitter as alpha acids that are isomerized by boiling (becoming iso-alpha acids, the primary bittering component in beer), but — here is the key — they are more soluable and will dissolve into beer during dry hopping to increase bitterness.
The devil is in the details:
– Baled hops (which is what almost all brewers previously used) contain less than 0.3% w/w (which basically means by weight), but the concentration can increase to .5% w/w after hop pelleting.
– Hops with a higher hop storage index (HSI – and when that is higher it means the hop loses its alpha acids more quickly) have a higher concentration of humulinones. This is variety dependent.
– Comparing a low-IBU beer to a high-IBU beer in order to understand the solubility characteristics of humulinones produced a surprising result. Increasing the dry hopping dose from 0 to 0.5, 1.0, and 2.0 pounds per barrel resulted in progressively lower iso-alpha acide consentrations, from 48 to 39, 35, and 30 ppm, respectively. “This siginifcant loss in bitterness was offset, however, by the large increase in humulinones that dissolved in the beer.”
– And the bitterness was different. I had to read this explanation slowly (I could feel my lips move): “Sensory evalutation of a very low IBU beer spiked with 22 ppm of humulinones was compared with the same beer spiked with 14.5 ppm of iso-alpha acids. The bitterness intensity of the two beers appeared to be similar, confirming that humulinones are about 66% as bitter as iso-alpha acids. 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.”
Moving on to pH.
Kurt Driesner, quality assurance manager at Urban Chestnut, discussed some of the early results of the brewery’s research at a MBAA meeting at UCB last month. Expect more information in a few months, but right now: typical dry hopping at UCBC increases pH between 0.1 and 0.25 units; preliminary data suggests that every 0.1 increase in pH is equivalent to a 2 IBU increase in perceived bitterness; and the perceived difference can be observed through pH adjustments independent of any dry hop addition.
S.S. Steiner also observed that pH increased as the dry hop dosage increased, so took five commercial beers with different IBUs and different pHs and dry hopped them with with Cascade hop pellets. The results showed that regardless of starting IBU or pH dry hopping had a linear impact on pH, with the pH rising by about 0.14 units per pound of hops used per barrel.