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Author: Marshall Schott

There are few things I worry less about when it comes to brewing than the type of fermentor I use, mostly because it seems like a variable inconsequential enough to have little if any impact on beer quality. I’ve heard arguments regarding the effect of fermentor geometry, amount of headspace, and O2 permeability, but in my experience, it has never seemed to matter.

Then I did the first fermentation vessel xBmt and was shocked that a majority of people were able to distinguish the sample fermented in a PET carboy from one fermented in a bucket. Given the small sample size of only 10 participants, I wondered if the results were a fluke, but 7 out of 10 people is pretty nuts, certainly enough to keep me curious. I was inspired to revisit this topic after reading a comment left by someone in a popular homebrewing forum about how they can “taste oxidation in beers fermented in plastic.”

Really?

| PURPOSE |

To evaluate the differences between beers produced using the same process where one was fermented in a PET carboy and the other in a glass carboy.

| METHODS |

Viewed by some as boring, California Common (aka Steam Beer) is one of my favorite styles, and thankfully I have friends who enjoy it as much as I do. Recently, a group of us agreed to make our own versions of Cal Common to be ready at the same time for an informal side-by-side comparison. With the results from the latest fermentation temperature xBmt still fresh on my mind, I designed a recipe somewhat different than What’re We Here For? and let the standard San Francisco Lager yeast sit this one out.

Vapor

Recipe Details Batch Size Boil Time IBU SRM Est. OG Est. FG ABV 5.5 gal 60 min 33.7 IBUs 12.0 SRM 1.053 1.010 5.6 % Actuals 1.052 1.009 5.6 % Fermentables Name Amount % Pale Malt, 2 row (Gambrinus) 9 lbs 82.76 Caramel/Crystal Malt - 60L 12 oz 6.9 Vienna Malt (Gambrinus) 8 oz 4.6 Victory Malt 6 oz 3.45 Pale Chocolate Malt 4 oz 2.3 Hops Name Amount Time Use Form Alpha % Northern Brewer 16 g 40 min Boil Pellet 10.1 Northern Brewer 25 g 15 min Boil Pellet 10.1 Northern Brewer 35 g 1 min Boil Pellet 10.1 Yeast Name Lab Attenuation Temperature Saflager Lager (W-34/70) DCL/Fermentis 75% 48°F - 59°F

Per my typical routine, I collected the water, made mineral and acid adjustments, then milled my grain the night prior to brewing.

The next morning, I immediately hit the flame to heat the strike water to temp.

About 15 minutes later, I transferred the slightly overheated strike water to my MLT, let it sit for a few minutes to preheat, then mashed in with the help of a couple cuties.

With the grain well incorporated, I measured the mash temperature to confirm I’d hit my target.

About 15 minutes into the mash, I pulled a small sample of sweet wort into a glass that had been chilling in my keezer, swirled it in a bowl of cold water until it reached room temperature, then took a pH reading. Bru’n Water works!

After a 60 minute rest, I performed a batch sparge, collecting my target pre-boil volume of wort and bringing it to a boil.

Hops were added during the 1 hour boil, after which the wort was quickly chilled to a few degrees warmer than my groundwater temperature, which at this time was 72°F/22°C. I then proceeded with racking equal amounts of wort to each carboy, gently stirring throughout to ensure equal distribution of kettle trub. The filled carboys were covered with foil and placed in a cool chamber, it took about 4 hours for both to stabilize at my target fermentation temperature of 60°F/16°C. I rehydrated two packs of Saflager W-34/70 in warm water for 15 minutes then evenly split the slurry between the carboys.

I returned 28 hours later to find the beer in the glass carboy actively fermenting, while the beer in the PET carboy looked dead.

I wondered if perhaps what I was seeing wasn’t kräusen but residual foam from the day before– is there something different about the foam retaining qualities of PET compared to glass? Either way, at 40 hours post-pitch, both beers were actively fermenting.

Things were looking a tad more similar 4 days in, the point at which I bumped the temperature in the chamber to 72°F/22°C to encourage complete attenuation and clean-up of any fermentation byproducts.

A check of the Fermometers on either batch revealed both were sitting squarely at my target.

Three days later, with fermentation on both beers appearing complete, I took hydrometer measurements that showed each was sitting at a desirably dry 1.009 SG.

I let them sit another 3 days before taking a confirmatory FG reading then starting the cold crash. The following morning, I fined each batch with gelatin then left them alone for another 2 days before packaging. The kegs were placed in my 38°F/3°C keezer and hit with 50 psi of CO2 for approximately 18 hours, after which I reduced the pressure to 14 psi where it remained. Both beers were beautifully clear and carbonated by the time I began collecting data 3 days later.

| RESULTS |

A total of 25 people participated in this xBmt, each blindly served 1 sample of the beer fermented in a PET carboy and 2 samples of the beer fermented in a glass carboy. While 13 tasters (p<0.05) would have had to accurately identified the odd-beer-out at this sample size, 14 (p=0.016) were able to do so, suggesting participants in this xBmt were reliably able to distinguish a beer fermented in glass from the same beer fermented in PET.

Following completion of the blind triangle test, those who correctly chose the unique sample were asked to compare only the 2 different beers and provide feedback on the one they preferred most. Strikingly, a majority of 10 tasters reported a preference for the beer fermented in glass, while 2 preferred the beer fermented in PET, 1 perceived no difference, and 1 reported no preference despite perceiving the samples as different.

After all of the data was collected, I disclosed the nature of the xBmt and asked my friends how confident they were in their selections, not a single one felt with any certainty they got it right. We proceeded to our planned Cal Common comparison. Standing in a circle of six, the few of us who participated began pouring samples for each other, the glass fermented beer was the first I shared. One round down, it was my turn to fill taster glasses with more Cal Common, only this time I poured from the growler of PET fermented beer, something I intentionally failed to inform my friends about. No one seemed to notice, all comments were consistent with those from the first round. I share this only to illustrate how similar these beers were despite being reliably distinguishable by participants intently focused on their differences.

My Impressions: I could not tell these beers apart. I thought I could after I correctly selected the odd-beer-out in the first blind triangle test served to me by a friend, but I was wrong more often than not in follow-up attempts. In the end, I had to accept I just couldn’t tell these beers apart, not in a triangle and not in a blind side-by-side comparison. The aroma, flavor, and mouthfeel were the same to me, which was curious given my generally congruent-with-results performance on the xBmts. Huh. As for the beer, it is, in my opinion, the best example of the style I’ve made to date. More dry, toasty, and quaffable than my What’re We Here For? recipe, which I have to believe is due to the different yeast given how similar the rest of the recipe is. Sorry, San Francisco, I’m sticking with Germany on this one.

| DISCUSSION |

“Are you effing kidding me?”

This was, in essence, the response I got from my friends once they completed the survey and I revealed the nature of this xBmt to them, most commenting that it seemed like a pretty lame variable to test since we all know it doesn’t make a difference. I don’t disagree, fermentation vessel wouldn’t seem to matter at all, but the numbers tell a different story. The shift in sentiment when I informed them of the fact a significant portion of participants had indeed been able to distinguish the beer fermented in the PET carboy from the one fermented in glass was hilariously palpable and invariably led to the follow-up question, “Which one did I prefer?” Of the four who were correct on the triangle test, two regularly ferment in glass, and they both preferred the beer fermented in their material of choice.

Boring as it may be, the fact two xBmts demonstrate an effect based on fermentor type has me wondering what exactly is responsible for the difference. For some, these results will serve to confirm the belief that PET’s oxygen permeability, minuscule as it is, has an appreciable impact on beer quality, which seems like the most logical assumption, though more solid data is required before I’m comfortable concluding anything.

Typically, likely as a function of bias, I detect the difference in the xBmts at least as often as the participants. That wasn’t the case this time, my performance on multiple triangle tests was no better than random while truly blind participants were able to reliably tell the beers apart. Besides causing me to question my palate, this made me wonder the extent to which my own unconscious confirmation bias was at play, keeping me from admitting that my long-held belief fermentor type has no impact could potentially be wrong. Either way, I’ve no plans to start using glass in my children toe laden brewery anytime soon.

What do you ferment in and do you think it makes a difference? Please share your thoughts in the comments section below!

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