Author: Greg Foster

As an admitted hophead, a badge I’ve worn proudly since I started brewing, there’s little I won’t do to improve the hop character of the beers I make. A few years back, during one of many haphazard Google searches for tricks to help take my IPA to the next level, I happened upon a fascinating thesis on dry hopping written by a well regarded hop researcher called Peter Wolfe. While a ton of interesting information is contained in this 79 page behemoth, there was one experiment that particularly piqued my interest. Mr. Wolfe tested the intriguing variable of agitating beer during the dry hop stage, which he discovered led to the quicker extraction of hop oils, accomplishing in mere hours what most believe requires days.

If a little agitation after adding dry hops could produce more hop aroma in less time, you better believe I was going to give it a try!

After engineering a couple wonky contraptions, I eventually realized the best solution to keeping my beer moving after adding dry hops was something I’d already done in a prior xBmt— toss a stir bar in a keg of beer, add the hop charge, and put it on my stir plate! I figured this might be an ideal way to employ this novel method without the complexity of extra pumps and hoses. Only one question remained: would agitation during the dry hop stage lead to amazing aroma in a significantly abbreviated amount of time? Time to find out for myself!

| METHODS |

I designed a simple Pale Ale for this xBmt with the intent of imparting most of the flavor and aroma characteristics from the dry hop.

Whirly Bird Pale Ale

Recipe Details Batch Size Boil Time IBU SRM Est. OG Est. FG ABV 5.5 gal 60 min 45.0 IBUs 6.7 SRM 1.056 1.016 5.4 % Actuals 1.056 1.011 5.9 % Fermentables Name Amount % ESB Pale Malt (Gambrinus) 10.5 lbs 90.32 Munich Malt - 10L 1.125 lbs 9.68 Hops Name Amount Time Use Form Alpha % Yakima Valley Hops Extract 4 g 60 min Boil Pellet 61 Cascade 18 g 10 min Boil Pellet 5.5 Simcoe 18 g 10 min Boil Pellet 13 Cascade 38 g 4 days Dry Hop Pellet 5.5 Citra 38 g 4 days Dry Hop Pellet 12 Galaxy 38 g 4 days Dry Hop Pellet 14 Simcoe 38 g 4 days Dry Hop Pellet 13 Yeast Name Lab Attenuation Temperature SafAle English Ale (S-04) DCL/Fermentis 73% 59°F - 75.2°F Safale American (US-05) DCL/Fermentis 77% 59°F - 75°F Notes Water Profile: Ca 108 | Mg 0 | Na 0 | Cl 35 | SO4 217

My brew day began with the usual ritual of weighing out and milling the grain.

I poured the pre-heated RO strike water into my mash tun, powered on the heating elements to maintain my target mash temperature, then added minerals and acid to achieve my desired water profile.

Next, I incorporated the crushed grain into the strike water, stirring gently before checking to make sure I’d hit my target mash temperature. I let my RIMS recirculate for a 60 minute sacchirfication rest.

With the mash complete, I transferred the sweet wort to my electric keggle, performed a batch sparge, and cranked up the power to bring it to a rolling boil, at which point I squirted in a syringe of slightly gross looking hop extract.

I left the wort to boil for 50 minutes before adding Whirlfloc and a modest amount of kettle hops, then 10 minutes later I proceeded with chilling the wort as quickly as possible.

A hydrometer measurement at this point showed the wort was at a respectable 1.056 OG.

I transferred the entire volume of cool wort to a 10 gallon corny keg and placed it in my temperature controlled chamber. I’d made a starter of harvested WLP001 California Ale yeast but for some reason it never really got going, so not wanting to risk a stalled fermentation or off-flavors, I improvised and went with a combination of US-05 and US-04 yeasts, which were rehydrated before pitching. Best of both worlds, dry yeast edition perhaps?

The yeast was pitched and the beer left to ferment at 65°F/18°C for 3 weeks before I took a hydrometer sample confirming FG had been reached.

In order to remove as much particulate as possible prior to introducing the dry hops, I cold crashed the beer for a few days, transferred to new kegs, then let them warm back up before moving forward. Time to introduce the variable.

I started by sanitizing two 3 gallon kegs and installing a stainless mesh filter around either dip tube before adding equal quantities of hop pellets to each vessel.

A stir bar was then dropped into the keg that would be agitated then both were sealed and purged with CO2 an unreasonable 15 times, my way of mitigating the anxiety of swirling already fermented beer. At this point, I used new gadget I’d recently constructed to transfer equal amounts of beer to both kegs simultaneously. It worked like a charm!

Of the various ways to test this variable out, we settled on the one thought to be a good starting point that involved immediately placing the agitated dry hop beer on the stir plate and leaving it for a mere hour.

With the spin cycle complete, I pressure transferred the agitated beer to a freshly sanitized and CO2 purged serving keg, which I held at room temperature. One batch down! The other beer was left unperturbed at room temperature for 4 days before I pressure transferred its contents to a similarly prepared serving keg, the stainless mesh filter doing an excellent job of preventing hop matter from clogging the dip tube.

Both kegs were placed in my keezer where they were allowed to slowly force carbonate over the following two weeks. By data collection time, they were looking quite nice!

| RESULTS |

A panel of 19 Strand Brewers Club members with varying levels of experience participated in this xBmt.

Each taster, blind to the variable being investigated, was served 1 sample of the agitated dry hop beer and 2 samples of the standard dry hop beer in different colored opaque cups then instructed to select the unique sample. While 11 correct selections would have been required to achieve statistical significance, only 3 tasters accurately identified the unique sample (p<0.05; p=0.96), indicating participants in this xBmt could not reliably distinguish a beer dry hopped for 1 hour with agitation from from one dry hopped over 4 days without agitation.

For those wondering if a significant portion of tasters chose either of the other 2 samples– nope. Of the 19 participants, 9 chose the red cup (p=0.15) and 7 chose the green cup (p=0.46), both of which contained the same exact beer. Randomness can be so random at times.

My Impressions: When I initially sampled these beers side-by-side, I thought I could tell the difference between them by smell alone, perceiving the standard dry hop beer as having a stronger hop aroma while the agitated dry hop version seemed to be missing some hop punch. Despite my confidence in being able to tell these beers apart, I proceeded to triangle test myself “blindly” 4 times for the sake of scientific rigor, carefully analyzing both smell and taste each time. As it turns out, my initial impression was completely wrong, I simply could not tell them apart, despite fully knowing what the variable was. Thankfully, both were also equally delicious.

| DISCUSSION |

It’s true that a non-significant xBmt result doesn’t prove that a certain variable doesn’t matter, we make it a point to say this often, as there’s always a possibility the thing tested would have a more noticeable impact in different situations. Then again, there are times where a statistically non-significant result actually holds some weight, particularly when the variable tested is purported to have a similar effect as the control to which it was compared. Such is the case with this xBmt.

Corroborating Mr. Wolfe’s prior findings that agitation of beer during the dry hop stage leads to rapid extraction of aromatic hop compounds, participants in this xBmt were unable to reliably distinguish a beer using an agitation method from one dry hopped without agitation for 4 days. It’s possible agitation didn’t actually play a role and that a non-agitated beer dry hopped for an hour would have extracted the same aromatics, something we intend to test out, though this would contradict prior xBmt findings showing dry hop duration does impact the perceptible characteristics of beer. I’m personally compelled to believe agitation made a difference, and while I’m not prepared to start touting its merits just yet because it is only a single data point, these results leave me feeling cautiously optimistic about the ability for agitation to allow for drastically reduced dry hopping and, consequently, grain to glass times.

This xBmt definitely leaves me wanting for more, in particular I’m curious if the hop character in the agitation dry hop beer might have been stronger immediately after the hour on the stir plate, maybe even enough that tasters would have been able to tell it apart form the standard dry hop sample. Yet another variable added to the list!

If you have thoughts about this xBmt, please share them in the comments section below!

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