Author: Greg Foster

When brainstorming new ideas and techniques to improve my brew, my thoughts often drift toward professional brewery practices. While commercial techniques don’t always scale down to the homebrew level, I figure the pros generally know what they are doing, so emulating their techniques is as good of a place to start as any. When I learned about professional breweries fermenting under pressure, I knew I had to give it a try.

What the heck is pressurized fermentation, anyway? The idea really is as simple as it sounds– find some way to pressurize the fermentation vessel and adjust the PSI as needed. A plastic or glass carboy is not going to work too well with this technique, as they’re unlikely to withstand the higher pressures. Luckily, many of us own corny kegs, which are designed to hold fairly high amounts of pressure, making them ideal for this application. The only other gear needed is an adjustable pressure relief valve, often referred to as a spunding valve, which is designed to maintain a set PSI while releasing any excess pressure. Unfortunately, off-the-shelf options are quite limited, but with a little research and a bit of DIY spirit, anyone can build their own spunding valve that’s right for the job, just like I did.

Perhaps you’re wondering what the purported benefits of fermenting beer under pressure are. After scouring numerous homebrewing forums, I discovered there are many theoretical advantages:

– The ability to ferment beer at warmer temps without increasing off flavors.

– Overall reduction in yeast ester and fusel production.

– Less vigorous fermentation with reduced krausen, meaning less headspace is necessary.

– Due to the closed fermentation, aroma compounds remain in the beer and aren’t blown off.

– CO2 generated from fermentation can be used to naturally carbonate the finished beer.

I’ve heard of professional breweries fermenting under pressure for a variety of the reasons listed above. It made sense to me– if you can ferment warmer while reducing off flavors then you can produce more beer faster, and more beer means increased profits. What brewery doesn’t want that?

I decided to email a few breweries to try to get some direct-from-the-source information about their fermentation practices. I was amazed so many wrote back to me! Gotta love how the professional brewing community is so open and willing to give back to homebrewers. Everyone I wrote to responded save for 2 I will not name, as it’s possible they were engaged in an epic battle over usage of a particular bolded font. Onto the responses I did receive, in paraphrased format:

Alpine Beer Co., Alpine, CA

Ferment at 68°F and 0 PSI (atmospheric pressure)

Bell’s Brewery, Galesburg, MI

It’s a trade secret, but the temp is on the warm side of normal; no mention of PSI

Stone Brewing Co., Escondido, CA

Ferment at precisely 72°F because house yeast goes to sleep under 70°F; 0 PSI

Ninkasi Brewing Co., Eugene, OR

Primary at 68°F and 0 PSI, cap fermentation at end of secondary to increase PSI

Societe Brewing Co., San Diego, CA

Pupil is fermented at 68°F PSI and 0 PSI

3 Floyds Brewing Co., Munster, IN

Usually 67°F for Ales and 50°F for lagers, both at 0 PSI

The Alchemist Brewery, Waterbury, VT

Always keep your cans of Heady Topper refrigerated!

Okay, so maybe pressurized fermentation isn’t nearly as prevalent as I thought. Some of the breweries I contacted mentioned they’d heard of others doing it, though none said they were actively using the method.

But this isn’t the whole story. Allow me to pontificate a bit on why the pros are still, in fact, fermenting under pressure.

You see those giant conical tanks? By nature of their size alone and the sheer amount of volume they hold, a ton of pressure is added during fermentation! Consider the fact that for every foot of liquid depth, the pressure is increased by .43 PSI. Knowing this, we can calculate that for a 15 foot tall conical fermentation tank, the pressure toward the bottom would be just above 6 PSI. While seemingly insubstantial, this amount of pressure is significantly more than what occurs in a typical homebrew carboy or bucket capped with an airlock. Is this having an impact on the quality of the finished beer? Maybe this is a variable that contributes to some of the differences in characteristics between homebrew and commercially brewed beer? Despite the fact the commercial brewers I reached out to aren’t actively fermenting their beer under pressure, I felt this topic was still very much worthy of further investigation!

| METHOD |

For this xBmt, I thought I’d try cloning a popular hoppy beer, 3 Floyds Zombie Dust. Since I’m a bit of a hophead, I was curious to see if the pressurized fermentation would help lock in those volatile hop flavors and aromas. That and, well, I just plain wanted some Zombie Dust on tap. I originally planned on hitting this beer with a 3 oz charge of Citra at dry hop but later decided the xBmt would be better served by skipping the dry hops altogether.

Zombie Dust Clone Recipe

Batch Size Boil Time IBU SRM OG FG ABV 8 gal 60 min 62 15.6 1.044 SG 1.012 SG 4.0 %

Fermentables

Name Amount % Domestic 2-Row 15 lbs 81.0 Munich (10L) 1 lbs 8 oz 8.1 CaraFoam 11 oz 3.6 C60 11 oz 3.6 Melanoidin Malt 11 oz 3.6

Hops

Name Amt Time Use Form Alpha % Citra 28 g First Wort Hop FWH Pellet Citra 21 g 60 min Boil Pellet Citra 28 g 15 min Boil Pellet Citra 28 g 7 min Boil Pellet Citra 28 g Flameout w/ 40 min rest at 205°F Boil Pellet Citra 56 g Flameout w/ 20 min rest at 180°F Boil Pellet 17.0

Yeast

Name Lab Attenuation Ferm Temp Safale S-04 Whitbread Dry Fermentis 70% 66°F

This batch would be my first using the BIAB method, it didn’t take much rigging of my brew stand make it ideal for the task.

As always seems to be the case whenever I try changing things up, things didn’t go nearly as smoothly as I had hoped. First, my target mash pH of 5.7 was way off of my 5.4 calculated pH. Even more alarming was the difference between my target and actual pre-boil OG, which ultimately led to a much lower OG than expected– .021 points lower! Lesson learned, I’ll mill finer next time.

After the boil was complete, equal amounts of wort were transferred into identical corny kegs repurposed as fermentation vessels.

The spunding valve was set to maintain 5-6 PSI throughout fermentation while the other keg was kept at atmospheric pressure using a simple blowoff tube.

Fermentation finished a few days later, the pressurized keg maintaining a steady 6 PSI, and I let both kegs remain in primary a few more days to allow the yeast to clean up after itself. When I returned, my previously pressurized keg had de-pressurized. Turns out my spunding valve had a very small leak that ultimately allowed for the full release of the CO2 I’d pressurized the keg with. I disconnected the now useless spunding valve and took a final hydrometer reading, both beers had attenuated to the same FG.

The beers were then cold crashed and kegged, ready to be served to tasters just a few days later. As far as I could tell, they looked identical to each other.

| RESULTS |

The majority of the data for this xBmt was collected during a Strand Brewers Club monthly meeting. Participants were presented with 2 samples from 1 batch and 1 sample from the other batch then asked to select which beer they perceived as being different. In all, 13 people participated in this xBmt including 2 BJCP certified judges, one BJCP provisional judge, and 3 homebrewers. In order to achieve statistical significance, 8 participants would have had to accurately select the different beer in the triangle test (p<.05). A total of 6 people correctly selected the beer that was different, which means statistical significance was not achieved (p=.33). While any further information extracted in this experiment is meaningless from a purely statistical perspective, I think it’s still interesting to look at how the participants responded to the follow-up questions on the survey.

In selecting which beer was different, participants were asked how confident they were in their selections. Their answers, grouped by whether they selected correctly or incorrectly on the triangle test, are as follows:

Correct/Incorrect

Not very confident: 0/2

Somewhat confident: 2/3

Very confident: 2/1

Absolute: 2/1

The 6 participants who were correct on the triangle test were asked to complete a comparative evaluation of only the 2 different beers, still unaware of which one had the variable manipulated. All 6 participants believed the aroma of the beers were somewhat similar and 5 reported preferring the aroma of the pressure fermented batch, with one person commenting it was “sharper and sweeter.”Regarding flavor, 5 tasters perceived the beers as being somewhat similar while 1 thought they were not at all similar. When it came to flavor preference, 4 tasters liked the pressure fermented batch better, with one person saying it was “hoppier tasting” while another taster described the flavor as being similar to “elephant piss.” All 6 participants thought the mouthfeel was somewhat similar with 4 of the 6 preferring that of the no-pressure batch.

My Impressions: Initially, I thought I noticed a difference between the beers. The aroma of the pressure fermented beer seemed just a bit stronger and sweeter compared to the no-pressure beer, characteristics that were also reported by one of the first participants. However, after repeatedly failing blind triangle tests, I accepted that I really couldn’t tell a difference. Yet again, as we’ve seen so often with these xBmts, bias was most likely at play.

For fun, and because I happened to have some Zombie Dust in my fridge, I compared my clone to the real deal.

Immediately upon tasting, it was pretty obvious that these were not the exact same beer, but they were pretty similar. The real Zombie Dust had a slightly sweeter aroma, which I believe is most likely due to the fact I didn’t dry hop my batch. Interestingly, of the 4 friends I had compare the 2 beers, all ended up preferring mine– go me!. But really, I won’t kid myself, they were biased as hell.

| DISCUSSION |

I’m not going to lie, I was hoping pressurized fermentation was going to have a bigger positive impact on the quality of my beer, mainly in terms of improved hop character. It just seemed logical that the increased pressure would trap and retain all of those delicate aromas and flavors I seek. Even though no statistically significant differences were discovered, there were nonetheless some aspects of pressurized fermentation I found to be real advantages. Having the fermentor pressurized made it incredibly easy to take a wort sample using a standard party/picnic tap, which is arguably more simple and sanitary than dipping the tip of a turkey baster into a carboy. Also, I experience a sense of comfort throughout the fermentation process because I knew there was zero chance of external oxygen or other contaminants making its way into my beer and potentially ruining the batch.

So, in the end, this xBmt didn’t reveal anything groundbreaking. Still, fermenting under pressure is something we as homebrewers know little about, which in my opinion is enough to warrant further exploration. For example, I’m curious about the claim that lager beers made with traditional lager yeasts can be fermented at ale temps and turned around in significantly less time when done so under pressure. It’s a fascinating technique that is going to require much more data before we start making any solid conclusions about its merits. It’s important to keep in mind this is only a single data point gleaned from an xBmt performed under specific conditions, and there are obvious limitations given the sample size. As such, interpret these results as they are intended– as interesting bits of novel information that hopefully inspire further investigation. I’m really looking forward to playing around with pressure fermentation more in the future!

Thanks again to those who participated in this xBmt! And an extra big thanks to the Strand Brewers Club for being nice enough to let some crazy new member suddenly start performing weird experiments on them.

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| Read More |

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