From Vol. 2, No. 8, December 2018
When I was at Oregon State University a couple of months ago I talked to Scott Lafontaine – Dr. Lafontaine since defending his PhD thesis early this month – about “Impact of harvest maturity on the aroma characteristics and chemistry of Cascade hops used for dry-hopping” (published in Food Chemistry) and a presentation at the MBAA-ASBC Beer Summit where he discussed this and more.
One thing I asked him about is why he chose the 16 hop volatiles to measure that he did. Reciting the details would constitute a bit of long form geekiness that even I must admit is a bit much. Some of them were included because they have become standard over decades. For instance, linalool is the “poster child for kettle hop aroma.” Others might have been included because they are proxies for still more compounds. And so on.
As brewers reimagine what beer might taste like scientists must reimagine what should be measured. Past research may have been perfectly valid, but that doesn’t mean it is relevant today.
“If you have them (particular compounds) and they are not correlating to flavor, then quit talking about them,” Lafontaine said. “As you change dynamics chemical reactions change.” Dry hopping, dry hopping in massive amounts, dry hopping during active fermentation, asking for hops kilned at lower temperatures, using more mature hops – these are all changing the dynamics.
“It comes down to people thinking about what in these hops, talking about hops. It is all about information transfer,” he said. “Not only that but correct information.”
A quick reminder: the research reported in Food Chemistry is specific to Cascade hops. The key takeaways were:
– Harvest maturity has a significant impact on the aroma of Cascade hops.
– Citrusy aroma in Cascades increases with harvest maturity.
– Late harvest Cascades have higher total oils and amounts of aroma volatiles.
– As Cascades mature, bound thiols increase while free thiols increase.
– Later harvested Cascades are likely to be better suited for dry hopping.
This study, part of it done with partnership with the French lab Nyseos, is the first to examine the impact of harvest maturity on thiol precursors and free thiols.
Lafontaine points out that this study was limited to Cascade hops harvested on one farm (over several years), and that: “Future work should explore the impact of harvest maturity for Cascade hops grown on other farms, in addition to examining other hop varieties that have been shown to have high concentrations of thiol precursors, such as Saaz, or free thiols, such as Citra. Investigating the maturity effect on the concentrations of free and bound thiols in these varieties may help identify the genetic pathways that make these varieties unique from a thiol perspective and also prevent off flavors (such as onion garlic notes) from forming due to other sulfur-related analytes in later harvested hops.
“Future studies should also investigate the impact of harvest maturity on the development of terpene glycosides, as this may explain some of the increase in geraniol and linalool during harvest.”
There is a lot to unpack here, and still more from his presentation at Beer Summit. That included results from studying both Cascade and Centennial hops during the 2014, 2015 and 2016 harvest on farms in Washington, Oregon and Idaho. Analysis included the 16 hop volatiles mentioned earlier. For one thing, it confirmed earlier research that overall hop aroma intensity (OHAI) and total hop oil are not directly correlated. Citrus quality and OHAI in Cascade are correlated, and total geraniol predicts Cascade dry-hop aroma better than total oil.
Centennial? Once again, concentrations of a single compound were better at predicting Centennial OHAI and citrus. But in this case it wasn’t geraniol, but beta-pinene. Different cultivars, different predictors. Obviously, more study is needed.
Interesting, and correct, as this information may be, is it useful for homebrewers or at small breweries whose brewers do not visit the American Northwest to select the hops they buy each year? (Imagine being able to say, “I’ll take some of those early harvest Citra hops” or “I’d like some Centennial rich in beta-pinene.”) Increasingly so, but we aren’t there yet. Vendors have begun to include information about compounds beyond the most prominent hydrocarbons. Measuring thiols is more difficult, and expensive, but progress is being made.
There are also opportunities for small breweries to work with local farmers; for instance to start asking about dry matter and understand what it means for a variety to be picked early or late. Sorry, this means a commitment that takes years, not a single harvest. Home hop growers can do the same, charting dry matter of everything they harvest.
I’ll leave the final word to Lafontaine, because I think analytics can show us what to look for without taking the art out of blending hops (with each other and in the brewing process).
“The rub is romantic,” he said. “But you are smelling things that don’t matter.”