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Author: Greg Foster

A growing trend in homebrewing over the last few years is fermenting in standard corny kegs, which allows brewers to employ certain methods some believe to be beneficial to beer. I started using kegs as fermentation vessels a couple years ago and have found it to be a very convenient way to significantly reduce oxygen from yeast pitch through serving. Admittedly, I presumed oxygen could have been the differentiating factor in the first two fermentation vessel xBmts (plastic bucket vs. PET carboy; glass carboy vs. PET carboy), which was validated by the non-significant results of the third iteration comparing a stainless Brew Bucket to a glass carboy.

However, I recently began to wonder about the impact of vessel dimension, specifically whether fermenting in a tall cylindrical keg produces a qualitative difference compared to beer fermented in other types of fermentors. By observation alone, it’s clear the surface area of the fermenting beer in a standard carboy is greater than in a tall, skinny keg, which means more contact with kräusen as well as whatever oxygen may be contained in the headspace.

Moreover, because of the smaller diameter of a keg, there is less contact between the beer and the yeast cake, which might also have an impact on flavors. It has also been theorized that tall fermentors facilitate more convection, enabling increased yeast contact with the wort that’s said to lead to lower ester production. Admittedly skeptical, given the results of prior xBmts, I was increasingly curious to test this out for myself!



| PURPOSE |

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

| METHODS |

I hadn’t had a big Amber Ale on tap in awhile and thought it’d be a good style to use for this xBmt, settling on a slightly modified version of a NHC winning recipe.

Amber Waves of Grain

Recipe Details Batch Size Boil Time IBU SRM Est. OG Est. FG ABV 5.5 gal 60 min 43.0 IBUs 16.6 SRM 1.072 1.015 7.6 % Actuals 1.072 1.012 7.9 % Fermentables Name Amount % ESB Pale Malt (Gambrinus) 14.25 lbs 90.48 Caramel/Crystal Malt -120L 11 oz 4.37 Victory Malt 11 oz 4.37 Chocolate Malt 2 oz 0.79 Hops Name Amount Time Use Form Alpha % HopShot 4 g 60 min Boil Pellet 65 Cascade 28 g 5 min Boil Pellet 5.5 Centennial 28 g 5 min Boil Pellet 10 Mosaic (HBC 369) 28 g 5 min Boil Pellet 12.3 Yeast Name Lab Attenuation Temperature Safale American (US-05) DCL/Fermentis 77% 59°F - 75°F Notes Water Profile: Ca 83 | Mg 0 | Na 0 | Cl 63 | 118

My brew day began with the usual excitement of weighing out and milling the grains.

With grains prepared, I began heating the full volume of brewing liquor, during which I measure out the mineral additions to achieve my target water profile.

Once strike temp had been reached, I stirred in the crushed grain and confirmed it hit my target mash temperature.

The mash rested for an hour, after which I transferred the wort to a keggle and used my Hot Rod heat sticks to bring it to a rolling boil, adding hops per the recipe. After a 60 minute boil, the wort was quickly chilled.

It was important to me that both vessels receive the same volume of wort, so I weighed both the keg and carboy empty and filled each based on weight, moving the hose back and forth in order to equalize any kettle trub that made it out of the the kettle.

A refractometer reading at this point showed the wort had reached my target 1.072 OG, which by my calculations, “required” about 1.5 packets of yeast apiece based on wort volume. I pitched equal amounts of rehydrated yeast into either batch of wort before placing them in my fermentation chamber controlled to 64°F/18°C.

Dry yeast always seems to take a little longer to become active compared to liquid yeast, which was certainly the case here, as both beers were still 24 hours after pitching. I decided not to worry and let things ride another day before. Sure enough, they were showing signs of fermentation at 48 hours post-pitch.

I slowly began raising the temperature in the chamber to 70°F/21°C a week into fermention in order to encourage complete attenuation. At the two week mark, I observed no bubbles in either of the airlocks and the kräusen on the beer in the carboy had dropped, signifying fermenation was likely complete.

I let the beers sit another few days before taking hydrometer measurements confirming both had settled at a similar FG.

I proceeded to cold crash the beers for a few days before racking to serving kegs. Since the purpose of this xBmt was to evaluate the impact of fermentor type, we decided it’d be best to treat both the same, which meant using CO2 to pressure transfer the beer from the glass carboy rather than using a standard siphon.

I’m not going to lie, I was a little concerned the glass carboy would explode and kill me.

The filled kegs were placed in my keezer where they received a brief burst carbonation before being set to serving pressure for a few more days of cold conditioning. Even without the use of gelatin, both beers looked similarly clear and beautiful when it came time to collect data.

| RESULTS |

A total of 29 people of varying levels of experience participated in this xBmt during a Strand Brewers Club meeting.

Each participant was blindly served 1 sample of the beer fermented in a corny keg and 2 samples of the beer fermented in a glass carboy. While the minimum number of correct responses required to reach statistical significance is 15 (p<0.05), a total of 16 tasters (p=0.013) accurately identified the unique sample. These results suggest participants in this xBmt were able to reliably distinguish a beer fermented in a corny keg from the same beer fermented in a glass carboy.

A brief comparative evaluation of only the two different beers was completed by the 16 participants who made the accurate selection on the triangle test, all remaining blind to the nature of the xBmt. The carboy fermented beer was preferred by 6 tasters, 3 reported liking the keg fermented beer more, 3 had no preference despite noticing a difference, and 4 felt there was no difference.

My Impressions: I attempted 3 “blind” triangle tests of my own, each time carefully smelling the samples before tasting them. My efforts were ultimately unrewarded as I only chose the correct sample one time, an outcome consistent with random guessing, which is exactly what it felt like I was doing each attempt. To my palate, the beers were too similar to tell apart. I do wonder if maybe my expectation that there wouldn’t be a difference somehow biased my performance on the triangle test, especially since participants were able to tell them apart. As for my take on the Amber Waves Of Grain recipe, this is the second time I’ve brewed it and the second time it has come out tasting absolutely delicious! I’d definitely recommend this recipe to anyone who enjoys this style as much as me.

| DISCUSSION |

Of the xBmt variables I’ve tested over the last few years, I viewed fermentation vessel as being one of the most unlikely to produce a distinguishable difference. Yet here we are, 3 out of 4 xBmts comparing different types of fermentors proving statistically significant. Mash temperature, hot-side aeration, cold-side oxidation– all factors I was convinced would have a noticeable impact but didn’t, while such an oft dismissed issue as the type of container beer is fermented in actually appears to have a qualitative impact. Crazy.

As an evangelist of fermenting in kegs, I absolutely plan to continue exploring the impact it has on beer, particularly when employing some of the methods unavailable when using other types of vessels. However, these results have caused me to question the approach, not only because of the statistically significant triangle test data, but because double the amount of tasters preferred the beer fermented in a glass carboy. Is it possible I’ve been making worse beer all this time? I don’t think so, but then again, I really like fermenting in kegs and hence am as biased as they come. Since preference is subjective and I really couldn’t tell the beers apart in my own trials, I won’t be making any drastic changes to my current practices. In the end, if fermenting in kegs somehow changes the character of my beer, so be it, it works for me.

If you have experience fermenting in kegs or have thought about this xBmt, please share them in the comments section below!

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