Author: Greg Foster
In my quest down the path of pressurized fermentation, I’ve become increasingly curious due to the fact both prior xBmts have shown it doesn’t seem to produce much of a noticeable difference. Ostensibly, establishing a relationship between pressure and flavor shouldn’t be particularly difficult, the lab science is pretty clear and there is a multitude of directly measurable flavor contributing differences caused by increasing pressure. But alas, I’ve yet to discover any large enough to register on my taste buds.
Pressurized fermentation is often cited as being used by larger breweries to facilitate faster lager fermentations at higher temperatures, a technique purported to suppress the esters typically expected from warmer ferments. Given the results of the last fermentation temperature xBmt suggesting a distinguishable difference between the same lager fermented at 60°F/16°C and 82°F/27°C, I wondered if pressurized fermentation might mitigate those differences and result in a beer more closely resembling one fermented at a lower temperature.
| PURPOSE |
To evaluate the differences between a split batch of the same lager beer fermented at 82°F/27°C under different pressures.
| METHODS |
Desiring a clean beer that would allow any off-flavors to shine, I brewed Marshall’s popular Munich Helles recipe for this xBmt, swapping out the noble hops for some Fuggles I happened to find in the back of my freezer. Everything in place, my brew day began with the crushing of the grain.
I adjusted my water profile with minerals and acid while the strike water was warming then, once to temp, mashed in and came close enough to hitting my intended 150°F/66°C mash temperature.
The wort was recirculated through my RIMS tube for a 60 minute single infusion rest after which I pumped it over to the kettle and brought it to a boil. Bagged kettle hops were added per the recipe and when the hour was up, I removed the hops and tossed in my immersion chiller. With the assistance of a pump, the wort quickly fell to my desired pitching temperature. Despite previous xBmt’s questioning the importance of oxygenation, I still chose to hit my wort with 1 minute of pure O2.
The wort was then split between three identical corny kegs (2 xBmts in one) that would all be used as primary fermentors. I dissolved four packets of 34/70 yeast in a single volume of lukewarm water before splitting the slurry evenly between the three fermentors.
The fermentation kegs were placed side by side in the same chamber set to a balmy 82°F/27°C where the yeast was pitched and the pressurized batch was hit with 12 psi of CO2.
I installed a spunding valve on the pressurized batch, an airlock on the non-pressurized batch, then left them to ferment. A day later, I noticed a fairly strong hiss of CO2 being released from the spunding valve, which was showing a 3-4 psi increase in pressure, while the airlock on the non-pressurized batch was bubbling away furiously. When I returned the following day, the airlock on the non-pressurized batch was completely still and the gauge on the pressurized batch had dropped back down to the starting pressure, no hiss to be heard. I allowed the beers to sit another day in the warm chamber before taking hydrometer measurements confirming both had reached the same 1.007 target FG.
I proceeded to cold crash the beers overnight then pressure transfer them to their final serving kegs where they were both injected with a gelatin solution.
When came time to collect data, the beers were carbonated and had cleared up nicely.
| RESULTS |
In all, a group of 20 people with varying degrees of experience participated in this xBmt during the monthly Strand Brewers Club meeting held at Honest Abe’s Cidery.
Each taster was blindly served 1 sample from the pressurized batch and 2 samples from the non-pressurized batch in opaque cups then asked to identify the one that was different. Given the sample size, 11 tasters (p<0.05) would have had to accurately identify the unique sample in order to achieve statistical significance. Ultimately, only 9 participants (p=0.19) made the correct selection, suggesting an inability to reliably distinguish a lager fermented warm under pressure from another fermented warm with no pressure.
Since significance was not reached, the evaluation of the two similar beers completed by only those participants who were correct on the triangle test is arguably meaningless. However, I thought the preference ratings were interesting enough to share and might quell some concerns of a false-negative. Each sample was rated as being preferred by three tasters, two endorsed no preference despite noticing a difference, and one taster reported perceiving no difference.
My Impressions: When I first sampled these beers, I immediately thought I could tell a difference. While both had the same distinctive sulfur-like aroma I noticed from the prior high fermentation temperature lager xBmt, I perceived it as slightly less pungent in the pressurized batch. After being correct on two self-served “blind” triangle tests, I accepted the difference was likely real and not my mind playing tricks on me. A week later, while collecting data, I decided to test myself again and, to my utter surprise, I got it wrong… three times in a row. Were my first attempts random luck or had something in the beers changed? I suppose I’ll never know. Either way, I could not tell a difference at that point, the beers were completely indistinguishable to me.
| DISCUSSION |
As the data on pressurized fermentation continues to suggest it may not seem to do very much, I find myself wondering if there are certain situations where it actually makes a difference. Large commercial breweries don’t adopt practices baselessly, so the fact many ferment their beer under pressure says to me they’re getting something out of it, but whatever it is seems to be too small for me to detect on a homebrew scale. If higher pressure is indeed a variable that can have a noticeable impact on fermentation, my repeated failed xBmts lead me to believe it may be recipe and/or yeast strain dependent. For me, it’s had no effect on IPA, Saison, and now Helles, so I’ll wait until there’s more hard evidence that a particular yeast strain at a particular temperature and a particular pressure results in noticeable differences. Until then, I’ll continue to ferment under pressure for no particularly good reason other than, hell, I just want to.
Is fermenting lager beers warm under pressure something you’ve thought about or even tried? Please share your thoughts in the comments section below!
If you have any thoughts about this xBmt, please do not hesitate to share in the comments section below!
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22 thoughts on “exBEERiment | Impact Of Pressurized Fermentation On A Warm Fermented Munich Helles”
Very interesting Xbmt. I think the results are more helpful than it would appear. I have considered moving to pressurized fermentation, not because of an improvement in flavor, though I think it might reduce the risk of oxidation, but more just to retain the CO2 for carbonation rather than recarbonating flat beer. I have asked pro Brewers in the past about pressurized fermentation, and the answers I got were really more about the economics of saving the CO2 costs and reduced labor costs from reduced tank transfers.
There are a whole lot of advantages to pressure fermentation unrelated to flavor. I love that once my batches start fermenting, the beer is kept completely oxygen free until the moment it pours in my glass.
I worked in a small craft brewery that fermented under pressure. This was my first brewery and I actually thought most did it this way. The major benefit was not needing a bright tank, being able to use the first keg as a yeast brink, and saving on CO2.
Aside from this, I think that CO2 is the major reason big brewery’s do it. Reduced ester production maybe, but most of the big guys blend anyways so I doubt that thats the big concern.
Greg, I see you’re using the big oxygen regulator. I use the same. What output setting do you use when running for 1 minute? Do you run it longer for higher gravity beers? I used 1/16 thinking smaller bubbles for the win for about 30-45 seconds. Then I re-read Williams Brewing instructions and they said 1/8 for 1 minute, if I remember correctly. I’ve never necessarily noted the difference between the two approaches, but I have questioned if I added too much oxygen in the past when I experienced browning of my final beer product–which suggests oxygenation.
For this xBmt, it was 1 minute at 3 liters/min for the whole 13 gallon batch. Really though, I’ve tried various levels of oxygenation and haven’t noticed any obvious differences.
Great write up, I really enjoyed it. I did have a quick question though. Maybe I read it wrong but was your fermentation complete in 2-3 days? Did you expect it to be that quick because of the high ferm temps?
I’ve been thinking a little about how on a small scale a number of these ‘truths’ seem to have no discernable effect or need to be pushed to extremes. One possible thought I had was volume to surface area during fermentation affecting the vapour/liquid equilibrium.
I remember a little bit of stuff you’ve done on fermenters, but it’s mostly been material based, if I’m right. Could be interesting to do a lager temp experiment x high/low surface volume ratio.
You might need 4 fermentation vessels though.
I think that most breweries that ferment under pressure are doing so as a carbonation method. Most of the small craft breweries here in central Europe naturally carbonate their beers. I am the only commercial small brewer in Slovakia that I know who force carbonates. So capping fermentation and letting the natural pressure carbonate the beer is the main goal.
So it would seem that you have have proven time and time again that the 34/70 yeast is amazing. Able to ferment at any temp and provide a clean crisp beer. Unfortunately it never gives any results other than that. Maybe go away from that yeast for tests like this and use a real lager yeast such as 800 or 833. Just seems like a waste of time.
That was my thought as well, that yeast strain plays a big part in all this. As an aside, I’d be interested in seeing what it looks like for wlp925, since that is specifically marketed as “high pressure lager”
Me too, I’m really hoping wlp925 makes it out of white labs’ vault
In what way is 34/70 not a ‘real’ yeast? It’s the weihenstephaner strain, which is a pretty good pedigree if you ask me!
“Large commercial breweries don’t adopt practices baselessly”
I find this an interesting comment as this whole website is devoted to testing the baselessly processes and procedures that were once written as scripture. I agree with those above that breweries are using pressure as a cost saving somewhere in the brewery and not for taste. This of course is just my thought and has not actual bases, but with your experiments it starts to be a viable answer.
Thanks for the great work guys.
this is absolutely true that a lot of practices are simply acceptable and unchallenged rather than logically found to be best practice.
on a commercial scale, you get plenty of data on tons of parameters over many trials even if not identical ones. there certainly is the possibility to investigate quite a few things.
What card game are you playing in the background of the final product picture?
Sheriff of Nottingham, awesome game
at the 60k bbl/year brewery where i worked, we noticed that freshly propped american ale yeast was incredibly clean in all of our beers but would begin exhibiting sulfur after 3-4 generations only in our hefeweizen. this persisted all the way into finished beer despite fermenting at 68F.
it seems likely this was related to grist, but we were more likely to scrap the beer than rework it, so i suggested we do some trials. i wanted to do parallel batches in our smallest tanks (30bbl) and close one on our normal schedule (~1°P > expected terminal, which we determined with a limit sample on a stir plate for every batch) and leave one valve open the entire time until we were ready to crash the beer.
we were unable to fit this into the schedule before i left, but i would have loved to have seen this through.
as to the economics of closing valves, i don’t believe it was the cost of co2 that propelled this practice. transferring carbonated beer required a receiving tank pressured to the equilibrium pressure, and all of this co2 would be vented and lost. thus it actually required quite a bit more co2 than we even captured via fermentation. the reason for it, at least where i worked, was to accelerate carbonation and shorten the gap between finishing fermentation and packaging the beer. tank hours are far more valuable than co2.
A friend from my brew club has bought the equipment to experiment with this. He claims to have heard a podcast in which a brew pub was able to turn beers around faster fermenting under pressure with no mention of flavor or overall quality. We have discussed fermenting under normal lager temps to see if fermenting with pressure will speed things up.
Hi, I’m trying over and again such in-keg fermentation but always my final gravity gets stuck somewhere 50% of the way. Recipies, water quality, ingredients and equipment all the same, only difference is normal fermenter versus in-keg fermentation.
Anyone having this as well? Any tips to overcome? Moreover: any tips to fix a half-way beer while already in-keg? Many thanks!
When you say “in-keg fermentation” do you mean ferment under pressure? If so, what pressure are you fermenting at? You should never get a stuck fermentation under pressure. I have never had a stuck fermentation so I can’t help there.
I have done a few pressure ferment lagers. But what I do is to leave the spunding valve open for the 1st 12hours or so and then cap it at 1bar. Leave it there for 3days a d then close the spunding fir a day or 2 before transferring to serving keg. Works everytime.
I have been fermenting under pressure for years and love it using my WilliamsWarn BrewKeg. #1 comment is that fermenting under pressure is not higher quality than non under pressure. It is equal to non pressure if fermented perfectly. So you will have less side effects in pressure fermenting than non pressure fermenting. #2 is that if you fermented higher than the 12psi you did, and did close to 16 – 20 psi you would have less sulfur or even none. #3 is 82F is pretty high. I know you were going for extremes but a normal room temp is ideal. For me in SoCal depending on time of year I ferment between 65F and 72F. No need for external expensive temp control. #4 pretty much an oxygen free ferment / transfer / store and dispense. #5 free CO2 carbonation. #6 From start of fermentation to fully carbonated great beer and drinking in 5-7 days. You can’t do that with non pressure fermenting.