Avoiding Dry Hop Oxidation
TroubleShooting
Chris Calcraft • Melbourne, Australia asks,
For the last few years, I have been growing my own hops in the backyard and using them to dry hop a hazy IPA. I recently finished Backyard NEIPA #3 and the issue that I am encountering is that I seem to be consistently oxidizing my brew. I have tried a few different techniques centered around purging the hops with CO2, but I always seem to end up with a sad, discolored, albeit dry hopped, final product. I tend not to dry my hops before using them, which I know can result in grassy flavors, but it is a convenient process — pick, purge, and rack the beer on them. Can you offer any tips to stop the oxidation? Is there a bit of equipment out there that I can use to process my hops into pellets to better remove oxygen before use? I am considering a vacuum bagger, but I don’t plan on storing so this seems wasteful.
Oxidation associated with dry hopping is a challenge faced by homebrewers and commercial brewers alike. The frustrating thing about this problem is the thin body of solid references related to the topic. Most brewers rightfully focus on moving hops into the fermenter with as little oxygen as possible. Strategies include the ones you reference; i.e., purging hops with CO2 and/or vacuum packaging, the use of special dry hop dosing chambers equipped with gas purging, and the use of pellet dissolving chambers/tanks where oxygen-free water is used to dissolve hops, possibly followed by CO2 purging, before adding to beer. These are solid approaches assuming that the root cause of oxidation is oxygen from the hops.
Metal ions, especially iron, copper, and manganese, are another cause of beer oxidation. Although brewers are generally not focused on metal ions in hops, hop cones are indeed possible sources of metal ions, especially when copper-containing fungicides are applied to hops. Although metal ions and hops sound like a possible smoking gun to explain oxidation associated with dry hopping, recent studies have concluded that beer oxidation is unlikely to be associated with metal ions from hops (Impact of Copper Fungicide Use in Hop Production on the Total Metal Content and Stability of Wort and Dry-Hopped Beer, Benjamin J. Chrisfield, et al.).
Another possibility, and one I can find no references about, is oxygen production from photosynthesis. This seems like an obvious possibility, but given the absence of any references about the subject leads me to believe that there is nothing to it. However, if we briefly peek down this rabbit hole there are a few possibilities to consider. Here is the idea: Hop cones picked while very green may contain more active photosynthetic enzymes than hops picked later in the season. You are adding wet hops, as do many brewers not wanting to mess around with hop kilning, and it is possible that photosynthetically active hop cones are adding oxygen to your beer. Sounds like a research project for an eager and hoppy young brewing student!
My last idea is that an exceptionally high hopping rate associated with a bumper crop of hops amplified the oxygen contribution that typically comes with dry hopping. Because you did not mention when you dry hopped, I will take the opportunity to speculate and guess that you added towards the end of fermentation when yeast activity had slowed. If this scenario is accurate, try adding your hops before the end of fermentation for next year’s harvest and allowing your active yeast population to mop up oxygen introduced by your hops. Hopefully one of these darts is close to the bullseye!
