exBEERiment | Impact Open Fermentation Has On A Festbier

Author: Jordan Folks

Typically, following the mash and boil, wort gets transferred to a fermenter, the yeast is pitched, then the fermenter is sealed to keep unwanted microbes and oxygen out during the fermentation process. However, some claim there are certain benefits to open fermentation, or fermenting beer in an unsealed vessel, such as optimal attenuation due to the constant exposure to oxygen as well the development of desirable esters.

Open fermentation is commonly associated with British styles, though historically, most beers were likely fermented in open containers including lagers. While pale lagers are known to possess clean fermentation profiles, it’s been claimed that open fermentation can encourage the formation of some esters that actually improve the flavor quality of the finished beer. In fact, it wasn’t until 1993 that Pilsner Urquell moved from open to closed fermenters, and Schönramer Brewing in Petting, Germany still relies on this approach to produce deliciously crisp pale lagers.

As a lover of all things lager, I’ve adopted numerous methods that I feel have led to an improvement in the versions I brew at home, though I’ve stuck with fermenting in closed vessels for the reasons listed above. Curious of the impact open fermentation would have on my annual Festbier, I designed an xBmt to test it out!

| PURPOSE |

To evaluate the differences between a Festbier that was fermented in an open vessel and one that was fermented in a sealed vessel.

| METHODS |

I went with a traditional Festbier recipe that I planned to serve at an annual Oktoberfest event. Special thanks to FH Steinbart for supplying the malt for this xBmt!

Festivaaal!

After collecting the full volume of water for two 5 gallon/19 liter batches, adjusting them to the same desired profile, and getting them heating up, I milled the grains.

When the waters per properly heated, I stirred in the grains and, seeing as this was a classic German lager, performed a step mash with a 40 minute rest at 144°F/62°C, 25 minute rest at 158°F/70°C, and 15 minute rest at 170°F/77°C.

During the mash rests, I prepared the kettle hop additions.

Once the mash rests were finished, I collected the worts and proceeded to boil them for 60 minutes, adding hops at the times listed in the recipe. When the boils were complete, I quickly chilled the worts with my JaDeD Brewing SS Coil Hydra before taking refractometer readings showing the worts were at the same OG.

After transferring identical volumes wort from each batch to sanitized fermentation kegs, they were placed in my chamber to finish chilling to be desired pitching temperature of 47°F/8°C before each received two pouches of Imperial Yeast L13 Global.

A this point, I loosely placed a piece of foil over one fermenter while the other was sealed with a blowoff tube connect, as I typically do.

The beers were left to ferment at 48°F/9°C for a week before I sealed the open fermentation keg to prevent post-fermentation oxidation. Next, the temperature of the beers were allowed to free-rise to 60°F/16°C over the following week for a diacetyl rest, at which point I took hydrometer measurements indicating a very slight difference in FG between the beers.

The beers were cold crashed to 33°F/0.5°C overnight then transferred them to CO2 purged serving kegs that were placed on gas in my keezer where they were left to condition for 4 weeks before they were ready for evaluation.

| RESULTS |

A total of 20 people of varying levels of experience participated in this xBmt. Each participant was served 1 sample of beer fermented in a sealed vessel and 2 samples of the beer fermented in an opemn vessel in different colored opaque cups then asked to identify the unique sample. While 11 tasters (p<0.05) would have had to accurately identify the unique sample in order to reach statistical significance, only 8 did (p=0.34), indicating participants in this xBmt were unable to reliably distinguish a Festbier that was fermented in a sealed vessel from one that was open fermented.

My Impressions: Out of the 5 semi-blind triangle tests I attempted, I correctly identified the odd-beer-out just twice. The aroma, flavor, and mouthfeel of these beers were similar enough to my palate as to make them indistinguishable, which wasn’t a bad thing, as both were great examples of Festbier – light and refreshing with ample malt and noble hop flavors.

| DISCUSSION |

Whereas open fermentation was likely how nearly all beers were made a century or so ago, it’s now viewed as a technique relied on primarily by British brewers or those opting to hang on to tradition. However, some believed it offers benefits over fermenting in sealed vessels, even for clean pale lager styles. Interestingly, tasters in this xBmt were unable to reliably distinguish a Festbier that was fermented in a sealed vessel from one that was open fermented.

One possible explanation for these results is that the yeast used for ferment these beers is simply not sensitive to the minor differences in pressure between open and sealed vessels, which may very well be different on the larger commercial scale. The fact these beers were perceptibly indistinguishable also indicates indicates the open fermented batch possessed no off-flavors associated with a contamination, which supports the use of a light covering such as foil to keep unwanted microbes out of the beer. As far as the difference in attenuation goes, it was minor enough to have been a function of something other than the variable, though regardless, it didn’t appear to have any notable impact on the quality of the beer.

As much as I appreciate relying on traditional brewing methods, this is only so if it has a positive impact on the beer, and that didn’t appear to be the case in this xBmt. Even though the open fermented batch demonstrated no signs of contamination by bacteria or wild yeast, it does introduce a vector for such exposure that I’d prefer to avoid, and hence I’ll continue to ferment my Festbier and other lagers in sealed vessels. That said, I look forward to continuing my exploration of open fermentation and will happily adopt the practice should future xBmts show it’s beneficial.

If you have any thoughts about this xBmt, please do not hesitate to share in the comments section below!

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