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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