exBEERiment | Impact Pressurized Fermentation Has On Saison

Author: Greg Foster

Support for this xBmt comes from House of Pendragon Brewing Company, producers of some of the finest craft beer in the Central Valley of California. Next time you’re in Fresno/Clovis, be sure to stop in for a pint!

In the first pressurized fermentation xBmt, I was curious to explore whether there was any truth to rumors that pressure somehow improved hop forward beers. Ultimately, neither the participants nor I were able to detect a difference between an IPA fermented at different pressures, but the responses I received critiquing the xBmt were nearly unanimous: pressure doesn’t affect hops, it affects yeast!

With my hophead curiosities temporarily satiated, it was time to begin looking into the relationship between pressure and yeast character. Theoretically, fermenting at higher than atmospheric pressure results in the suppression of flavors imparted by the yeast (1, 2, 3, 4). The xBmt I originally had planned, the one I thought would be most interesting, would have explored whether increased pressure suppresses yeast off-flavors in a clean lager beer fermented warm. However, as I started gearing up for this xBmt, something happened that caused me to change my course– the results of the 3rd fermentation temperature xBmt were published, the one where a rather large group of qualified tasters were unable to reliably distinguish between lager beers fermented 16°F apart.

Who knew making flawed beer would be so difficult?

Since warm fermented lagers cannot be counted on to be severely flawed, I decided to look into how pressurized fermentation might affect a beer style I am absolutely certain contributes plenty of yeasty character: Belgian Saison!

| PURPOSE |

To evaluate the differences between a split batch of the same Saison fermented under different pressures.

| METHODS |

As you may recall from the previous pressure xBmt, I ran into some difficulty with a leaky spunding valve, the device used to maintain a certain level of CO2 in a fermentor. In an attempt to avoid repeating this annoying situation, and always happy to play with new equipment, the gear geek in me built another one. Behold, spunding valve 3.0!

Very similar to the one Sean Terrill built, I am happy to report this valve does not leak! While the pressure relief valve this unit is built around is reasonably priced and rather easy to obtain, it’s unfortunately a bit wonky to set properly, almost as if the psi scale has no correlation with reality. With a little trial and error, I was able to coax the gizmo within the ballpark of my desired psi.

I shamelessly used Ed Coffey’s The Farmer in the Rye Saison recipe as a base, using all EKG hops and selecting a yeast strain I’ve experienced as producing the funky Belgian esters and phenolics I so desire in my Saison– The Yeast Bay’s Wallonian Farmhouse.

Three days prior to brewing, I made a large yeast starter. The brew day went smoothly thanks to the assistance provided by my brew buddy, Maggie, who prefers the comforts of a plastic tub to more conventional seating.

While Ed recommends mashing at 148°F, I aimed for 151°F and nailed it perfectly.

I set my RIMS to recirculate the wort for an hour before batch sparging, transferring it to the kettle, then boiling away.

I added the hops and kept an eye out for boilovers during the 90 minute boil, after which I chilled the wort using my homemade counterflow chiller then split it evenly between 2 fermentation kegs… aaaactually, I split the wort 3 ways, pitching The Yeast Bay’s Northeastern Abbey yeast into the non-xBmt batch, for variety’s sake. It was around this time Maggie decided to see if she fit in my bottle storage cupboard.

With wort prepared, I decanted the starter that had been cold crashing overnight and split it evenly between both fermentors. I then pressurized 1 keg with CO2 before attaching my new and improved spunding valve to the gas post. Hoping to restrain the flavor contribution of the yeast, I set the pressurized batch to a fairly high 8 psi, while the non-pressurized batch was left to ferment at atmospheric pressure. Both fermentors were then placed in a 72°F fermentation chamber. The following day, I returned to ramp the temperature and noticed the spunding valve had indeed maintained the set 8 psi. Sweet! I left the kegs alone for another day, at which point I found the pressure had increased by 0.5 psi, almost certainly as a result of the CO2 produce by the active yeast. After increasing the temperature to 74°F, I bumped the pressure on the spunding valve up a bit for the pressurized batch then bid them adieu for the night. After 3 days, the pressurized keg was sitting at 9 psi and I decided to take a hydrometer reading to see how things were moving along.

Both beers measured 1.030 SG, an indication that fermentation was progressing equally regardless of pressure. I slowly raised the pressure in increments over the next couple days until it reached 13 psi, at which point I checked the SG again.

Fermentation seemed to have slowed down a bit, though both batches had dropped another 0.010 points. Here’s where things went a little screwy. I had to leave the kegs alone for a week while I went on vacation, so I again increased the pressure on the pressurized batch a teensy bit before heading out. When I returned, I was surprised to find it sitting at 17 psi. Curious of the impact this may have had, I took yet another hydrometer reading.

While the non-pressurized batch finished at 1.006 SG, the pressurized beer seemed to have halted at 1.009 SG. In an attempt to encourage a bit more attenuation out of the pressurized batch, I decreased the pressure to 11 psi, raised the temp to 75°F, and gave the keg a little shake. A few days later I found that my persistence had paid off, yielding a final gravity of 1.007 SG.

I forgot to take a side-by-side picture of the finished beers before one of the kegs kicked, but to my untrained eye, they appeared to be virtually indistinguishable.

| RESULTS |

Data for this xBmt was gathered at the monthly Pacific Gravity homebrewers club meeting where a group consisting of 21 magnanimous homebrewers and beer judges graciously agreed to participate. Each participant was provided 3 samples of beer served in identical opaque cups, 2 from the pressurized batch and 1 from the non-pressurized batch. 

In order to achieve statistical significance, at least 11 of the 21 (p<0.05) participants would be required to correctly select the odd beer out. In the end, only 6 tasters (p=0.68) were able to correctly identify the unique sample, which is statistically less than what we would expect by random chance alone, allowing us to conclude that fermenting the same Saison wort under different pressures did not produce beers that were reliably distinguishable.

As a matter of course, those participants who were correct on the triangle test proceeded to complete a comparative evaluation of the 2 different beers, still unaware of the nature of the xBmt. Since the results were not significant, this data is essentially meaningless, but I’ll share some of it anyway, trusting everyone understands its futility. Responses to questions about flavor, aroma, and mouthfeel differences were inconsistent. Of the 6 correct participants, 5 reported preferring the non-pressurized sample. When asked which beer they thought was fermented under only atmospheric conditions, 5 tasters chose the correct beer.

My Impressions: I participated in multiple quasi-blind triangle tests to see if I could discern any difference between the beers. Unsurprisingly, no matter how hard I focused, I couldn’t tell the beers apart. They looked the same, smelled the same, and tasted the same. Because of this, obviously, I did not prefer one over the other and thought both were fine Saisons. 

So, what about the beer fermented with The Yeast Bay’s Northeastern Abbey strain? It turned out great, easily winning my preference over the Wallonian fermented xBmt beers. If you’re into spicy, earthy Belgian character with subtle hints of pear, you really ought to consider trying this strain out.

| DISCUSSION |

For the second time now, results seem to suggest pressurized fermentation produces little if any discernible differences when compared to the same beer fermented at atmospheric pressure. I’m curious if these results carryover into professional brewing where significant levels of hydrostatic pressure occur naturally during fermentation due to the size of the tanks. Even my intimate involvement in this xBmt, from planning it out to sharing the beers with participants, wasn’t enough for me to notice any differences at all. To my palate, these beers were the same, which corroborates the experiences of the majority of participants. 

A somewhat interesting and quantifiable observation in this xBmt was the discrepancy in SG toward the end of fermentation, which ultimately resulted in the pressurized beer finishing 0.001 SG point higher than the non-pressurized batch. While arguably a nil difference, getting the pressurized batch to fully attenuate took some serious yeast whispering on my part. This got me thinking about something I’d previously read about, a theory of Drew Beechum’s suggesting certain Saison strains are sensitive to the back-pressure created in a fermentor simply by using an airlock, hence the common reports of stalled fermentations. The fact the pressurized fermentation in this xBmt stalled may lend some credence to this idea, though it behooves us to consider the fact I used a different strain of yeast than he discusses and the amount of pressure I intentionally hit the fermentor with is far higher than what one would expect from the back-pressure created by an airlock alone. Interestingly, fermentation activity in the pressurized batch restarted when I lowered the pressure to about 13 psi, still far more than the back-pressure created in an airlocked carboy (~0.5 psi).

Fermenting under pressure is one of those variables we know little about in terms of how it impacts homebrew, and as such I believe it is worthy of further investigation. I’m certainly not comfortable making any generalized claims of certainty regarding the effect higher psi fermentations have on beer, although based on my experience and the results of these xBmts, it appears to have less of an impact than I originally expected.

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How-to: Make a lager in less than a month 

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