Author: Brian Hall

Oxidation is one of the more common off-flavors found in beer and, aside from a full-blown infection, one of the more offensive. With flavor descriptors like wet cardboard, musty, and hard candy, it’s no wonder brewers work so hard to keep oxygen from damaging their beer, especially on the cold-side, once fermentation is complete.

Professional brewers have developed an array of methods and tools to keep beer as fresh as possible, and while homebrewers can’t replicate them all, many have begun to filter down. One vector of oxygen ingress is the suck-back that occurs during the cold-crash step, which can be accounted for by pumping CO2 at low psi into the fermentation vessel during this process.

Then there’s packaging, which is perhaps the riskiest point in terms of cold-side oxidation. An easy method brewers who keg have been using for years is to purge the otherwise non-purged keg’s headspace with CO2 once it’s filled with beer, then release it; this usually occurs 5 or more times to rid as much oxygen as possible. However, fearing this isn’t enough, some take things a bit further and fully purge the vessel of oxygen by using CO2 to push sanitizer out prior to filling it with beer.

I’ve been kegging with the headspace purge method for years and oxidation hasn’t been a big issue for me, but it’s hard to ignore the grotesque photos of purple NEIPA that pop up so often on beer and brewing forums. Inspired by a past xBmt demonstrating the negative impact cold-side oxidation has on NEIPA, I adopted the slightly more complicated full keg purge method, even when making styles that aren’t of the hazy-hoppy sort. Curious to see how the methods compare with a less notably sensitive beer style, I put it to the test with a pale lager.

| PURPOSE |

To evaluate the differences between a Czech Pilsner transferred to a keg fully purged of oxygen and the same beer transferred to an open keg that had the headspace purged.

| METHODS |

The recipe I went with for this xBmt was modeled after one of my favorites, pFriem Pilsner.

Rockin’ In The Free(m) World

Recipe Details Batch Size Boil Time IBU SRM Est. OG Est. FG ABV 5.5 gal 60 min 35.4 IBUs 3.5 SRM 1.050 1.007 5.7 % Actuals 1.05 1.006 5.8 % Fermentables Name Amount % Pilsner (2 Row) Ger 9.625 lbs 95.68 Carafoam 4.96 oz 3.08 Acid Malt 2 oz 1.24 Hops Name Amount Time Use Form Alpha % Perle 17 g 60 min Boil Pellet 8.3 Tettnang 8 g 60 min Boil Pellet 4.2 Tettnang 21 g 10 min Boil Pellet 4.2 Saphir 14 g 10 min Boil Pellet 3.7 Select Spalt 14 g 10 min Boil Pellet 5.1 Tettnang 21 g 10 min Aroma Pellet 4.2 Saphir 14 g 10 min Aroma Pellet 3.7 Select Spalt 14 g 10 min Aroma Pellet 5.1 Yeast Name Lab Attenuation Temperature Global (L13) Imperial Yeast 75% 46°F - 56°F Notes Water Profile: Ca 65 | Mg 0 | Na 0 | SO4 45 | Cl 40 | pH 5.5 Download Download this recipe's BeerXML file

I started my brew day by lighting the flame beneath the water I’d previously adjusted, after which I weighed out and milled the grains for a single 10 gallon/38 liter batch.

In sticking with what I’ve heard pFriem does, I employed a step mash for this beer, initially hitting 142°F/61°C before ramping it up to 157°F/69°C for a second rest.

Following a 60 minute mash, I removed the grains then began heating the wort.

Following a 90 minute boil, I quickly chilled the wort.

A hydrometer measurement confirmed the wort was at the target OG.

I let the wort sit covered in my cold garage overnight, returning 10 hours later to evenly split the clear, cool wort between identical Brew Buckets. After pitching a single pouch of Imperial Yeast L13 Global, I placed the vessels next to each other in my fermentation chamber controlled to 50°F/10°C.

After 2 weeks of fermentation, I began raising the temperature in the chamber to 67°F/18°C for a diacetyl rest and to encourage complete attenuation. Hydrometer measurements taken a couple weeks later showed both beers achieved the same FG, indicating they were ready to be packaged.

I racked the beer from one batch into a sanitized keg that was not purged of oxygen, leaving the airlock off of the Brew Bucket lid to allow air to be sucked in as the beer flowed out.

For the low cold-side oxidation batch, I first purged a keg by using CO2 to push sanitizer out of it.

Next, I pressure transferred the beer to the keg by pumping CO2 at low psi into the airlock hole on the Brew Bucket lid.

The filled kegs were placed next to each other in my cold keezer. At this point, I proceeded to hit the non-purged keg with 4 sets where they were left to carbonate and lager for a few weeks before they were ready to serve to tasters.

| RESULTS |

A total of 19 people of varying levels of experience participated in this xBmt. Each participant was served 2 samples of the beer kegged with little effort to reduce oxidation and 1 sample of the low cold-side oxidation beer 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 6 (p=0.65) did, indicating participants in this xBmt were unable to reliably distinguish a Czech Pilsner pressure transferred to a keg purged of oxygen from one racked to a non-purged keg.

My Impressions: I was unable to tell these beers apart during any part of the process, even after a couple months of aging. They looked, smelled, and tasted the same every time I sampled them, which is evident by my inability to pick the odd-beer-out in various triangle tests. While not quite the pFriem clone I hoped for, this beer was still tasty and crushable.



| DISCUSSION |

The negative impact of cold-side oxidation has been given increased attention with the rise of NEIPA, but it’s still believed to be detrimental for all beer styles, hence the effort brewers employ to keep it to a minimum. The fact tasters were unable to distinguish a Czech Pilsner racked to a keg fully purged of oxygen from one racked to an open keg with a series of headspace purges suggests both methods were equally as effective.

In considering these results in light of those from a past significant xBmt looking at cold-side oxidation in NEIPA, one plausible explanation for these results is that certain styles are simply more sensitive to oxidation than others. Maybe it has to do with hop amounts, yeast strain, ABV, or something else entirely. That’s not to say a pale lager packaged carelessly won’t eventually start to show signs of detriment before one kegged using stricter methods, but it’s possible the effects of cold-side oxidation take hold more slowly in certain styles.

I’ve brewed a wide variety of styles using all sorts of kegging techniques, from siphoning out of a carboy into an open keg to fully closed transfers into purged kegs. Unlike others I’ve heard from, I haven’t noticed any major differences in terms of oxidation in my beers; they all look and taste similar to me. Maybe I’ve been lucky. Or maybe purging the headspace after filling is good enough. Either way, I still plan to use closed transfers when packaging beer, regardless of the style, because it’s cheap insurance.

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

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