Author: Marshall Schott

The bane of many a commercial brewery’s existence, post-fermentation oxidation is said to have a negative impact on overall flavor stability of beer, reducing shelf-life and leading to profit losses. Because of this, large amounts of effort and money are invested in eliminating as much oxygen as possible from coming into contact with the finished beer. As a homebrewer, I’ll admit to not concerning myself too much with the issue of shelf-life, as the huge majority of beer I make is consumed within 3-4 weeks of packaging, which is typically only 5-8 weeks from the day it was brewed. This is one of the badass benefits of making our own beer! However, I’m aware of many homebrewers who go to great lengths using myriad methods to reduce oxygen ingress at packaging, believing that doing so will extend the freshness of their beer and preserve the precious hop character in styles like Pale Ale and IPA.

I consider my kegging method to be a sort of hybrid closed transfer system where I bottom-fill sealed kegs through the liquid post without purging with CO2 beforehand. My admittedly naïve thinking is that by gently filling from the bottom, the large majority of oxygen is pushed up and out of the keg through the gas post (or PRV for ball lock users), and that residual CO2 in the beer is released via agitations, creating a blanket atop the beer as it fills. I could be wrong, but based on feedback from friends and comments on competition scoresheets, it seems to be working pretty well, as oxidation off-flavors have never been an issue for me. With all the talk lately of people pushing sanitizer out of kegs with CO2 prior to filling to ensure O2-free packaging, I became curious of how a beer packaged with an intentionally poor process would compare to the same beer kegged using my standard method and designed an xBmt to test it out!

| PURPOSE |

To evaluate the differences between a beer packaged under conditions promoting high oxidation and the same beer packaged under relatively low oxidation conditions.

| METHODS |

Given reports of oxidation having a strong impact on hop character, I decided to double the batch size of the Centennial single hop beer we recently covered for The Hop Chronicles use it to test this variable.

2 Birds, 1 Stone Pale Ale

Recipe Details Batch Size Boil Time IBU SRM Est. OG Est. FG ABV 11 gal 60 min 37.0 IBUs 5.3 SRM 1.057 1.012 5.9 % Actuals 1.057 1.012 5.9 % Fermentables Name Amount % ESB Pale Malt (Gambrinus) 15.25 lbs 68.54 Pilsner (Weyermann) 7 lbs 31.46 Hops Name Amount Time Use Form Alpha % Centennial 30 g 60 min Boil Pellet 7.3 Centennial 20 g 30 min Boil Pellet 7.3 Centennial 60 g 15 min Boil Pellet 7.3 Centennial 60 g 5 min Boil Pellet 7.3 Centennial 104 g 3 days Dry Hop Pellet 7.3 Yeast Name Lab Attenuation Temperature Safale American (US-05) DCL/Fermentis 77% 59°F - 75°F Notes Water Profile: Ca 87 | Mg 1 | Na 10 | SO4 125 | Cl 62 | HCO3 200

The night before brewing, I collected the water for this full volume no sparge batch, adjusting it with minerals and acid to my target profile, then weighed out and milled the grain.

I hit the flame under my kettle first thing the next morning, adding the slightly overheated liquor to my mash tun for a 5 minute preheat, then mashed in with some help from my adorable assistant, Hazel.

With the grain fully incorporated into the brewing liquor, I measured the temperature and found I was right about where I wanted to be.

About 15 minutes into the mash, I pulled a small sample for a mash pH reading, it was precisely where Bru’n Water predicted.

After a 60 minute rest, I collected the full volume of sweet wort in my trusty graduated bucket then transferred it to the kettle.

When the wort reached a rolling boil, I set a timer for 60 minutes and made hop additions according to the recipe.

At the conclusion of the boil, I quickly chilled the wort to a few degrees warmer than my groundwater temperature, which was a bit warmer than my desired fermentation temperature.

A refractometer measurement showed I’d hit my target OG.

The chilled wort was evenly split between two fermentors and placed in my cool chamber to finish chilling to my target fermentation temperature of 66°F/19°F.

I returned about 4 hours later to pitch vitality starters I’d made earlier with Safale US-05 dry yeast. The following morning, about 12 hours later, I noticed airlock activity indicating active fermentation in both fermentors. I allowed the beers to ferment for 3 days before bumping the temperature up to 72°F/22°C. With signs of active fermentation absent after another 3 days, 6 days total, I took preliminary hydrometer measurements and added the dry hop charge.

After 3 days on the dry hops, I took a second hydrometer measurement that matched the first, confirming fermentation was indeed complete.

The beers were cold crashed overnight then fined with gelatin before I proceeded to the packaging phase where the variable was introduced. For the normal batch, I used my typical method of transferring the beer from the fermentor to a sealed and non-purged keg through the liquid-out post, a depressor on the gas post to allow air out as the beer fills the keg.

In order to maximize oxidation in the experimental batch, I cut a small length of vinyl tubing, attached one end to the spout on my Brew Bucket, dangled the other end in the unsealed keg, opened the valve, and let the beer splash into the keg.

The filled kegs were placed in my keezer where they underwent a brief period of burst carbonation before I reduced the gas to serving pressure. Then I let them sit for 4 full weeks because, at least according to many reports, oxidation requires time to really screw a beer up. After a month of waiting, both beers were equally clear and carbonated, not to mention remarkably similar in color.

| RESULTS |

At total of 24 people of varying levels of experience participated in this xBmt. Each taster was served 1 sample of the beer packaged under normal conditions and 2 samples of the beer packaged with high oxidation in different colored opaque cups then asked to select the unique sample. While 13 (p<0.05) would have had to accurately select the unique sample in order to achieve significance, only 11 (p=0.14) chose correctly, suggesting participants in this xBmt were unable to reliably distinguish a Pale Ale kegged with high oxidation from the same beer kegged using more standard procedures.

Since significance was not reached, any subsequent data is ostensibly meaningless, so please interpret the following with caution. Those tasters who were correct on the triangle test were instructed to complete a brief evaluation of preference comparing only the 2 different beers. Still blind to the variable, 4 people preferred the non-oxidized sample, 2 said the liked the oxidized sample more, 3 tasters reported perceiving a difference but had no preference for either sample, and 2 felt there was no difference between the beers.

My Impressions: Appearance isn’t an aspect paid attention to during the triangle tests, but it’s something I was very curious about with this xBmt, as oxidation is known to darken beer. Because of this, I fully expected, particularly after a month in the kegs, the high oxidation beer to be noticeably darker than the beer packaged under normal conditions, but that just wasn’t the case, they looked exactly the same. What about aroma, flavor, and mouthfeel? In order to test my ability to distinguish between these beers, I attempted 10 triangle tests, my wife serving me “blindly” and randomly selecting the sample that was unique. In total, I was correct 3 times, no better than random guessing, which is admittedly exactly how it felt. I experienced both beers as one dimensional and boring, though notably clean with no detectable off-flavors.

| DISCUSSION |

Oxygen is real and, despite the results of this xBmt demonstrating tasters could not reliably distinguish a beer that was highly oxidized at packaging from one that wasn’t, I’ve no doubt its effect on beer is equally as real. What I do wonder is the extent to which oxidation during packaging is an issue beer that’s consumed within standard homebrewer timeframes. In a non-scientific poll of a bunch of brewer friends, all of them said the majority of the beer they make is consumed within about 3 weeks of packaging. Of course, it’s certainly possible my normal kegging routine, which it seems is fairly popular among homebrewers, introduces more oxygen to the beer than I thought, though it’s hard for me to believe that amount would be similar to intentionally splashing beer during packaging. And to boot, in discussions with tasters following completion of the triangle test, not a single one described either sample as having any hint of oxidation character, rather the most common comment was that it was clean and otherwise boring, a sentiment I wholly agree with.

These results got me thinking about something that’s been on my mind a lot lately, which is our ability to detect and accurately identify commonly discussed off-flavors. I recall an experience during my BJCP tasting exam where one of the beers, as we learned after the fact, was intentionally oxidized during packaging– apparently, the proctor had another homebrewer who wasn’t taking the exam bottle beers off his taps in a manner that would impart obvious oxidation character. In post-exam commiseration, I learned only one out of about 10 of us noted oxidation (wasn’t me), which at the time I figured others and myself missed because of being overly focused on everything else. However, these days I’m left wondering if perhaps certain off-flavors are more elusive than I’d originally presumed.

Just to be clear, in no way should results like these be viewed as advocacy for a particular method, because they are not. We evaluate variables because we’re interested in learning more about their impact on beer, not because we think people should pay no mind to them. Personally, I’ve no plans to change my kegging practices, as I still view oxidation during packaging as potentially perilous, though I’m now more interested than ever to evaluate the impact of packaging into a CO2 purged kegged.

If you have thoughts on oxidation during packaging or experiences of your own with this variable, please feel free to share them in the comments section below!

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