March 4, 2016 by fhsteinbart
There was a recent article published which looked at isomerization of alpha acids in hops at varying pH’s and temperatures. What was most interesting was that higher temperatures gave better utilization figures than raising pH. At higher (more alkaline) pH, hops take on an annoying soapy flavor that wasn’t discussed in the article. What was illuminating is that the research showed what I personally have found out, and that is increasing temperature will increase the isomerization rate dramatically. I’ve used my Presto 8 quart pressure cooker to isomerize a small amount (¼ ounce) of hops (Magnum) in a ½ gallon boil for 15 minutes, and have seen IBU’s hover around the 150 IBU mark. At 250° F, and at 25 PSI, this sits right on the curve that the researchers made showing higher temps vs. time. While I don’t think that everyone will benefit from high(er) pressure brewing, we all should at least be boiling hops for a minimum of 90 minutes, to as much as 120 minutes to get the
maximum value of iso-alpha acids in our beers. This of course assumes a pH range of 5.2~5.6, which is the more usual and customary expected range that brewer’s work with in brewing a well crafted beer. Researcher’s at Oregon State University have also done gas chromatographic analysis of hop utilization over time and discovered that given any hop, the curves seem very similar despite variety, which speaks more to the chemistry of hops in general than of minor discrepancies within each varietal. The curve shows maximum utilization and highest IBU isomerization at 90 minutes, with maximum flavor contribution at 20 minutes, and maximum aroma contribution at 7 minutes. Looking at these times, I would also add the time it takes to empty your kettle as it cools to pitching temperature into this model, as isomerization, and flavor and aroma development continue during this time interval. So let’s go brew some beer!