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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37 thoughts on “exBEERiment | Impact Pressurized Fermentation Has On An American Pale Ale”
You think you lost flavor due to the leak?
Feels to me like you’d want to try again with that leak fixed, but also do a pressurised transfer to a secondary for dry hop, and finally a pressurised transfer to the serving keg.
Definitely want to do it again without that stupid leak. Not sure I’d want to dry hop though, it could mask any really subtle aroma differences.
I think you discovered why so few breweries use pressurized fermentation….it just doesn’t make a difference.
The brewers that DO (supposedly) perform pressurized fermentation are typically maco brewers and are (supposedly) doing it to suppress esters. But really, all brewers performing fermentation in FV’s bigger than a few bbls are subjecting their fermentation to greater pressures – as describe by Greg above – due to the water column. which is (supposedly) why they are often quoted as have a few degrees higher fermentation temps than we HBers can typically get away with.
* – All info is above potentially complete BS.. hehehee.
I remember hearing Charlie Bamforth mention (in a Beersmith podcast) that Fosters in particular have been doing it for a while. I wonder if that’s because the energy and time required to get macro amounts of lager wort down to traditionally low temperatures in a warmer climate like that of Australia is such that it’s more efficient to go a bit warmer and pressurise the ferment to keep the esters down.
Did you transfer it from primary to secondary, or serving keg? Or did you just dispense the yeast with the party tap and then carb and serve? Even if the results are similar, I would love to skip cleaning carboys!
I just transfer directly to serving keg, I don’t see any need to secondary if I’m not dry hopping. My process is to cold crash for a day or two to compact the trub and drop the yeast. Then I use a party tap to take a sample which has the added benefit of getting rid of the yeast/trub near the dip tube. Then I pressure transfer from the primary to the serving keg and serve.
There was a German Master Brewer in my area that fermented his Lagers under pressure, he was Doemens trained, and fermented at 8 psi in his 5 bbl fermenters. Maybe if you asked more German trained brewers you might get more data, as he claimed this was common in his craft. He said he had to get his spunding valves from Germany, as there were none here.
what about an open fermentation vs under airllock exbeeriment? i’m interested in what your triangle tests will show on flavour perception- there was a relative brewingtv episode if i recall correctly. cheers for the great posts from greece!
That one is definitely on the list!
I read the whole article, and now I seriously want to share a beer with you over a game of Settlers…
I am always down for some beer and Catan!
Hi, a list of spund pressures in german (and in metric units) can be found here : http://www.uelus-homebrew.ch/text/Spundungsdrucktabelle.pdf
A relevant pressure at 66F (19°C) would be 26psi (1.8 bar).
And I have to note one other thing: “DIY spirit” and pressurized vessels don’t go together, at least at pressures above one bar. Even 0.4 bar or 6 psi can hurt quite bad.
Anyway, keep up your good work!
Franconia brewing in McKinney, TX does ferm under pressure to naturally carbonate. You could contact them. They’re pretty friendly and do almost exclusively lagers.
Thanks, I’ll try to remember to contact them before my next pressure experiment
Pressure fermentation for German breweries is primarily so they can avoid having to add CO2 which is forbidden by German law. It’s not a flavour consideration for most brewers doing it
You fermented at 66F for both batches? Is this ambient or controlled? If it was controlled, I’m not sure that this test has much purpose, since that’s a fairly decent fermentation temperature for clean beer. Maybe try to get the non-pressure keg to push off flavors. Bump it up to 68-72F ambient and let it ride. That would really determine if the pressure is helping keep things under control.
Temperature was controlled for this first experiment. I’m definitely going to try much higher temperatures in some of the follow up experiments, really try to get some yeasty off flavors
Did this second experiment happen? I am currently fermenting a couple stouts with S04, under 15PSI, at ambient temp(the beer is upwards of 76F). I’m hoping to suppress esters. My thanksgiving turkey is taking up space, thawing, in my fermentation chamber. I hope I don’t get fruity esters….
Howdy Greg,
I have also started experimenting with pressurised fermentation, I am led to believe the benefits are more pronounced for lager production as opposed to ales given that it is yeast growth that is supposed to contribute the off flavours that lagering takes so long to remove.The other obvious benefit is CO2 retention if such economy is important to you. However I cannot yet report any added benefits in my trials yet other than saving a bit of CO2.
But I do think that the it is a misconception that fermenting under pressure will lock in hop aroma or any other desirable aromas…if you use a spunding valve then when that valve reaches release pressure it does just that…release gas with all the aroma contained therein that gas. In fact, once the set pressure is reached, you release the same number of molecules of gas per unit time as you would if you fermented at atmospheric pressure. assuming the rate of fermentation is the same. ie you reach the same dynamic state of molecules of gas production per unit time, but just at a different pressure. Granted, at the end of the process you have retained a bit more gas than would have been ordinarily released to the atmosphere, but I doubt it is significant in the scheme of things.
I hope this makes sense.
Fermentation under cover pressure is done by (some) large macro lager brewers to suppress esters. In Germany it is sometimes also done to preserve the CO2 in solution. You can essentially cap the vessel post krausen with a spunding valve to carbonate. Think a few above already alluded to this. May it have other benefits and draw backs – potentially.
Siskiyou Brew Works in McCloud, CA ferments under pressure. They are a very small brewery/pizza house (1.5 barrel, if I recall correctly.)
Hi Greg, great experiment, very interesting. I think that the reason why there were not big differences is in the fermentation temperature used. The real advantage of this technique is the high temperature that speed up the fermentation. The huge breweries (AB In Bev, Heineken, etc.) ferment their lagers at 77˚F under pressure. In this way (and with a very high oxygenation) they complete a fermentation of high gravity beer (OG 1.080) in 4 days reducing to a minimum the esters production. I don’t say that these companies are synonym of quality and these extremes impact on the final beer flavor. But this is the reason why this technique was developed. For a craft brewer ferment an ale at 77 ˚F instead of 68 ˚C means that you can shorten the primary fermentation of a couple of days without an impact on flavor. For an home brewer it’s nothing but for a professional brewer is money and nowadays with so many breweries on the market it is important to be efficient.
Steff
I’m not sure where the reasoning of higher pressure means you can ferment at higher temperature. As you increase pressure you increase temperature, without bringing in EOS and activity coefficients, for arguments sake just take a look at the ideal gas law PV=nRT. I’d be interested in conducting this experiment with a batch under pressure and one with a heating element so that the temperatures of the two are consistent and seeing if the temp is the cause of flavor difference.
It’s not in relation to Pv=nRT, which may hold true for gas/temp/ vol relationships on a given space, rather this refers to the theory (actually proven but perhaps not relevant at the HB scale) that increased pressure on yeast suppresses their ester and phenol production.
Some macro lager brewers reported use or have at least toyed with the process.
Hi Greg:
Excellent article. Do you think keeping finished beer under pressure in secondary fermentation would produce superior results vs. non-pressurized conditioning? Some writers in the 1800s felt porter matured for many months in huge vats was superior because of the natural pressure exerted on the bulk of the beer. Thanks.
Gary
Mmmmmm Beeeer.
Hi Greg, very interesting article. I think it will be hard to notice off flavour differences on tastier beers so probably the best test would be a Kolsch or Lager. I would definitely place money on open fermentation producing more odd/off flavours but it depends on the environment too. However, at 0 PSI i would think it would almost be the same as under pressure all bar the lack of carbonation, which i think is a massive bonus when brewing for me.
I ferment in a Williamswarn (dubbed WW) personal brewery, whether all grain or extract wort. I use this because it has wonderful temperature control and features for dumping sediment, tasting and kegging beers easily. I have found from open fermenting and dry hopping bigger beers such as IPA’s and Tripels, that it is simply slower and messier. I then have to wait typically 3 good days for carbonation to be right for those i transferred from an open fermenter. I still produced good beers but i am convinced they are higher in DMS. Hard to tell with these stronger beers though. I have noticed that i can get very clean lagers (i mean surprisingly so) brewed very quickly at higher Ale temperatures in the WW… so maybe for off flavours in lagers and lighter ales like a Kolsch, pressure fermenting is the key. I know from speaking to the owner and designer of the WW (he was a master brewer for Tiger and Heineken) that many european breweries use pressure – i am guessing that this is mainly because most of the beers they produce are lagers of sorts and if you can produce crisp clean lagers faster at higher temps then your ahead of the rest and production is higher. I would say this is where it is being used. More so than tastier beers or Ales where flavour profiles are not as clean or noticeably off in any manner. It might be very debatable but all i know is this seems to be the case.
Pressure fermenting first and foremost offers carbonation at the same time as fermentation and this saves a lot of time. So in my WW, after crash cooling for 12 hours and maybe 1 clarification using colloidal silicon, i can run off my first hopped Ale in about 8-10 days. If it is a basic beer, an Ale is about 7-8 days. A lager about 10. Bigger tastier beers that i open ferment, dry hop and transfer to the WW are often like 15-20 days before they are good to drink. Dry hopping in the WW is harder because there is no easy way to add the hops after fermentation as the vessel is pressured, so i experimented with dry hopping and fermenting all at once. An IPA i did recently where i dry hopped right from word go in the WW, i produced my first 70IBU 6% IPA in 12 days to drinking with really good results. Fermentation was done and dusted in 5 days and i brewed at 23 C or 73.5 F. The lagers i tend to start at 15 and then finish at 18 C (59-64F). But i have had good success with lagers at over 20 C or 68 F. I am about to try one at 23 C (73.5F) based on some info i recently read.
I have never done a back to back like you did. However, all the brews i do under pressure in the WW are far superior i guess for a few reasons. The system is closed – so once it is sanitised and a brew put down in it, nothing is open or left to chance right through to kegging. Because i can tap off a brew straight from the system and taste it before kegging, i can decide if the beer is right. This means i can modify if need be. I can make additions with the sediment bottle at the bottom and re-inject hops or other flavouring after the brew is complete and do this without getting any air into the system.
I have spent the last 3 years producing better beers than i could ever have done prior. I have been brewing on and off since 1980. So for me, this is a time saver, gadget reducer and clean closed system for making great consistently clean beer. No more messy garage with buckets and pumps etc. I am over the mess and extra gadgetry that this eliminates let alone being ecstatic over the results i get. However, if i bought something again, it would simply be a larger glycol fermenter that handles pressure and make a few mods to it so i can do what i can with this WW machine.
I would agree with Dean,
I have a conical glycol jacketed fermenter which is pressure rated up to 1.5bar (25psi). I often ferment in this fermenter at the full 1.5 bar pressure rating and i can tell you that the results are superior. This was not a cheap thank to have made but it’s absolutely awesome and i serve beer directly from the fermenter.
You can ferment faster and/or ferment at higher temperatures and get cleaner results.
I would also agree with Dean and say that fermenting under pressure is the best way to ensure you have minimal oxygen contact. If you are serious about quality beer then this matters.
It’s true that many large breweries do not ferment at elevated pressures by I would imagine that the cost of the tanks is part of the reason. To manufacture a pressure rated tank and a non pressure rated tank is a significant difference in engineering and it’s not uncommon for the tanks to cost 50% more to build plus they require periodic inspection.
I have seen this product that looks quite interesting and I may try and get hold of one of these soon to try out:
http://www.oxebar.com.au/fermentasaurus/
I can’t seem to find much information about this product yet though so i am not sure if it’s in production or not yet.
More pressure… 6psi is not enough…
Try again with 20+psi and see if there is a difference!
It will also be more beneficial for less hoppy beers. The hops tend to mask any slight off flavours from the yeast, making them harder to perceive. Brew a 20IBU lager side by side and see if there is a difference.
Awesome! I’d really love to see what happens to two batches, one under pressure and one airlocked, when fermented at 72-73. I have a Fermentasaurus that I’ve yet to use and I’m wondering if fermenting under pressure at room temp would be a viable option or just an exercise in massive ester production.
Shout out to such a great Brulosophy team for doing this! I’ve been searching on the web for how to’s on pressure fermenting and this is one of the few.
That said, I think this is really the key to great lager and Kolsch style beers. I’m currently reading “Kolsch: History, Brewing Techniques, Recipes” by Eric Warner and he goes into great detail how Kolsch producers stress the importance of fermenting under pressure.
I know this has been done in the past, but pleaaaaaase do it once more with your ‘new’ and better triangle test and compare fermentation under pressure with higher than usual temperatures (e.g. for a lager) to see if it allows homebrewers to cut down on their fermentation times. There recently have been plenty of youtube videos (especially from Scandinavia) about it. Even though the recent trend of Kveik yeast (and faster fermentation schedules) might actually bias their results, another pressurized experiment would be appreciated.
What about the first 2×2 exBEERiment? Divide a batch by four, two yeasts, two different pressures and see what the results are?
👍 Good experiment. I found this article very interesting. I was wondering if pressure slowed down fermentation because I assumed it’s like running up hill for the yeast to produce CO2 under pressure vs level ground.
Howdy, as some have eluded to the biggest reason we use sounding valves is to help with natural carbonation. In Germany you cannot use co2 to force carbonate so they ferment under pressure and then use some fresh wort to build even more pressure at the end of the process to get the dissolved volumes to the desired levels. Here at Four Generals we specialize in German biers but being in America we can force carbonate so we take advantage of that for finish volumes only on lager biers. By fermenting under pressure I have been able to lower my monthly CO2 bills (haven’t hit the break even on the valves quite yet but am getting close) and I believe off of personal sampling that I have a finer carbonation in the biers. I have not tried fermenting any warmer with the valves but our fermentation times are quicker then your average Homebrew as we always have ideal conditions. We do proper lagering on our beers so they tie up tanks for 6-10 weeks on average depending on starting Plato but the spunding valves have seemed to help with turn times just a little as in the beers are matured a touch quicker.
(To answer the original question we use a pressure of .6 bar during fermentation on fully adjustable valves)
Hope this helps.
Prost -Ross
Head brewer- Four Generals Brewing
I’m sorry, but after doing a relatively scientific experiment, you still felt the need to continue after realizing that both batches fermented at 0 psi because of a leak? You eliminated what should have been the only variable between the two.
I wouldn’t have put this out until you fixed the leak and started over.
Pretty frustrating outcome and a waste of experimenting and excitement if you ask me.
I’d pressure ferment under 15 psi.
This xBmt was published 4.5 years ago…