Tuesday, February 12, 2013

Recirculating Dry Hops: Extract More Aroma Oil in Less Time

1-DSC_0402When I think of a good “hoppy” beer, my mind conjures up interesting aroma and flavor profiles. Bitterness units barely factor in. A hop forward beer that has lost (or never really had) aroma becomes a boring and uninteresting beer.

What if you could get more aroma oil extracted from your dry hops with less time? Would you do it? That question almost sounds rhetorical.

Early last year I came across an Indie Hops blog post titled, “More Aroma Oil, Faster: The Dry Hopster’s Holy Grail.” With a title like that, I had to keep reading. The post cited a study by Peter Wolfe and Dr. Tom Shellhammer at the Oregon State University Department of Food Science which compared the aroma/flavor potential of two dry hopping materials (whole cone hops vs. pelletized hops) and the effectiveness of two methods for dry hopping (stirred vs. unstirred). All dry hopping took place at 23.2°C (73.76°F). Both sensory analysis (a tasting panel) and instrument analysis (measurements of compounds) were performed on samples taken at 0.5 hours, 2 hours, 4 hours, 6 hours, 24 hours, 4 days, 7 days, and 12 days of exposure to hops.

Peter Wolfe’s thesis, A Study of Factors Affecting the Extraction of Flavor When Dry Hopping Beer, is published on Oregon State University’s website. I read all 92 pages of it, which took me a while because I found myself searching Google every other page to research a new [to me] unfamiliar term.  There were several interesting findings in the study. Here are a few highlights:
  • Pelletized hops resulted in faster extraction and more hop aromatic compounds compared to dry hopping with whole cone hops.
  • Stirring hops resulted in higher overall aroma compound extraction and more intense aroma perception than unstirred hops.
  • Stirred pellet hop aroma compounds were nearly fully extracted after 24 hours.
“Say what? 24 hours?!”  (That was my reaction, anyway.)
instrument analysis chart
sensory evaluation chart

Aroma, Aroma, Aroma

As pervasive of a practice as dry hopping is in modern beer brewing, there is a lot of confusion as to what is exactly going on during the dry hopping process. This gives rise to all kinds of practices and procedures for how to achieve the best results. This post is not attempting to address every aspect of dry hopping (bitterness contribution, antimicrobial properties, etc.). For that, I would recommend reading Peter Wolfe’s thesis as well as the book, For the Love of Hops, by Stan Hieronymus.  This post is only addressing the primary goal of dry hopping: aroma.

important aroma compounds derived from hopsBy far, the greatest reason that dry hops are used today is to add hop aroma and flavor (a combination of aroma, taste and mouthfeel) to beer. While other hop components (alpha/beta acids, polyphenols, glycosides and bio-transformed hop compounds) affect the overall flavor experience (see section 1.3 of Wolfe’s Thesis), the primary components of hops that directly contribute to aroma while dry hopping are terpene oils and sulfur compounds. The goal when dry hopping is to extract those compounds out of the hops and into the beer.

Most homebrewers follow a similar procedure to one another when dry hopping: steep the hops in fermented beer. Regardless of whether whole cone or pelletized hops are used, if hops are placed in bags or allowed to free float, or if the dry hops are added to the primary, secondary or keg, the universal practice for dry hopping at the homebrewing level is to allow the hops to soak in beer post fermentation without any form of agitation.

On the other hand, the commercial breweries that are best known for aromatically hoppy beers all use some form of agitation or extraction beyond simply steeping the hops in the beer. Dogfish Head, Russian River Brewing and Firestone Walker use a “Hop Cannon,” Sierra Nevada uses a “Torpedo,” and New Belgium and Stone use “The Slurry Method” (chapter 8, For the Love of Hops). Commercial breweries have efficiency and time constraint requirements that homebrewers do not have, but as Peter Wolfe found in his study, a greater level of hop aroma compounds are extracted through agitation.

My dry hop agitation setup

After reading Peter Wolfe’s thesis, I was determined to come up with a way to agitate dry hops at the homebrewer level. The first idea was to build some sort of false bottom stir plate for my fermentation fridge, and then spin a large stirbar in a glass carboy to agitate the hops (I still like this idea). However, I recently obtained a stainless steel conical fermentor and wanted to move my fermentation of hoppy beers to the conical. What I came up with was the following setup, which as it turns out is almost exactly the same setup that was used for agitation in the study conducted by Peter Wolfe (I ran it by him).

Below is a diagram (and below that, a video) of how I do my dry hop agitation. The setup is slightly different than what is pictured below. I do not own a Blichmann brand conical, and I use the standard inline head rather than the center inlet head. I’m also sans a racking cane on the conical at the moment. I would highly recommend one is used with this setup. Without a racking cane, hop matter will come through the racking arm port. It will require a significant amount of dumps from the bottom to get all of the hops out. I waste a lot of beer dumping hops out of the bottom before I have clean enough beer to rack to a keg. A racking cane will allow the tube to point up and out of the hop slurry so that clean beer can be racked without having to dump any hops.

Here is a YouTube video of my setup in action:
Continuously recirculating dry hops in the fermentor

What you’ll need

Assuming you already own a conical fermentor, to pull this off you’re looking at purchasing the following:

Non-conical fermentor configurations:

I have not attempted this in any fermentor other than my conical. I would like to see how other brewers approach this situation with carboys and Sanke kegs. If you have recommendations to share in the comments, please do so.
In addition to the stirbar idea that I mentioned above, a carboy cap can be modified to accommodate two racking canes, like this. You can then follow a very similar process to what I did with my setup. You would want to ensure the hole was not cut too large, because oxygen making its way in will be counterproductive to the goal of making an aromatic hoppy beer. If you would rather use a stopper than a carboy cap, Morebeer sells a #6.5 stopper with 2-holes, but the 2nd hole is too small for a racking cane, which means that changes would be needed. A ball valve would need to be added to this configuration to be able to adjust the flow rate of the pump.
Sanke kegs:
Before I purchased my conical, I used the Sanke fermentor kit from BrewersHardware. As with the carboy cap above, the blowoff hole could be modified to accommodate a 2nd racking cane.

Results to come in a follow-up post. Stay tuned...