Author: Brian Hall

It’s been surmised that fermenting in a semi-permeable vessel with a relatively large amount of headspace increases the likelihood of the beer coming into contact with the surrounding atmosphere, which is presumed to lead to undesirable off-flavors. This concern has led to the common recommendation to ferment with as little headspace as feasibly possible, leaving just enough to contain the kräusen that develops during active fermentation.

Results form a previous xBmt on this subject showed tasters were generally capable of telling apart beers fermented with different amounts of headspace. However, one caveat to the xBmt was that different volumes of beer were fermented in identical vessels, leading me to wonder if it was headspace alone that was responsible for the significant finding.

With evidence supporting the notion that oxygen detrimentally affects beer, it seems plausible that a larger amount of headspace might increase the potential for oxygen ingress into the fermentor that leads to unwanted flavors. If this is true, those who enjoy brewing the occasional smaller experimental batch using their regular sized gear may want to reconsider their approach. However, if the difference noted by tasters in the aforementioned xBmt was due more to differences in beer volume, then keeping that constant while varying the amount of headspace ought to yield different results. I decided to test it out for myself.

| PURPOSE |

To evaluate the differences between beers fermented with varying amounts of headspace when beer volume is consistent.

| METHODS |

Given the apparent sensitivity to oxygen of New England IPA, I thought it a good style to test this variable as well as another one I was curious about, so I brewed up a 20 gallon batch.

Happily Hazy

Recipe Details Batch Size Boil Time IBU SRM Est. OG Est. FG ABV 5.5 gal 60 min 103.5 IBUs 6.4 SRM 1.070 1.013 7.5 % Actuals 1.07 1.014 7.5 % Fermentables Name Amount % Pelton Pilsner Style Malt (Mecca Grade) 7 lbs 46.29 Lamonta American Style Pale Malt (Mecca Grade) 6 lbs 39.68 Crystal 15 Patagonia 1.125 lbs 7.44 Sugar, Table (Sucrose) 0.996 lbs 6.59 Hops Name Amount Time Use Form Alpha % Magnum 6 g 60 min Boil Pellet 12 Citra 34 g 20 min Boil Pellet 12 Cryo - Citra 28 g 20 min Boil Pellet 25 Citra 85 g 5 min Boil Pellet 12 Citra 85 g 1 min Boil Pellet 12 Citra 85 g 6 days Dry Hop Pellet 12 Yeast Name Lab Attenuation Temperature Barbarian (A04) Imperial Yeast 74% 62°F - 70°F Notes Water Profile: Ca 117 | Mg 3 | Na 10 | SO4 84 | Cl 168

Download Download this recipe's BeerXML file

I started off this brew day by using my sous vide machine to warm up the RO water, which I’d previously collected and adjusted to my desired profile.

While waiting for the water to come to temperature, I weighed out and milled the grain.

Once the water was slightly warmer than target, I transferred it to my 55 gallon/208 liter mash tun then incorporated the grains to achieve my desired mash temperature.

The full volume mash was left alone for a 60 minute saccharification rest.

When the mash was complete, I began collection of the sweet wort.

With the wort homogenized and split between a couple kettles, I brought it to a boil, during which hops were added as laid out in the recipe.

After the 60 minute boil, I quickly chilled the wort with my immersion chiller.

A hydrometer measurement revealed the OG of the wort was right where I expected.

It was time to introduce the variable. In order to test the impact of headspace while keeping volume constant, I racked 4.25 gallons/16 liters of wort to either a 5 gallon/19 liter glass carboy or 6.5 gallon/25 liter glass carboy. Seeing as both carboys had the same diameter, this would lead to a difference in headspace of approximately 1.5 gallons/6 liters. Both batches were hit with the same dose of pure oxygen.

Using some leftover wort, I made a couple starters with Imperial Yeast A04 Barbarian that got pitched the next morning.

Both batches were equally as active just hours after pitching and dry hop additions were added during fermentation a couple days later. With signs of fermentation absent after 2 weeks, I took hydrometer measurements confirming both beers had reached the same 1.014 FG then racked each into CO2 purged kegs.

The beers were given a week to condition and carbonate in my keezer before they were ready to serve.

| RESULTS |

A total of 21 people of varying levels of experience participated in this xBmt. Each participant was served 2 samples of the beer fermented with a normal amount of headspace and 1 sample of the beer fermented with a larger amount of headspace in different colored opaque cups then asked to identify the unique sample. A total of 12 tasters (p<0.05) would have had to accurately identify the unique sample in order to reach statistical significance, though only 5 did (p=0.89), indicating participants in this xBmt were unable to reliably distinguish a NEIPA fermented under a typical amount of headspace from one fermented under a larger amount of headspace when beer volume was identical.

My Impressions: Similar to most the tasters, I was unable to tell a difference between these beers with any consistency. Even in side-by-side tastings where I knew the beers in each cup were different, they tasted identical to me. And the beer was delicious! Inspired by Lawson’s Sip of Sunshine, this is one of the original recipes that got me hooked on on both NEIPA and single hop Citra beers years ago. While possessing some haze, it was not a turbid, soupy, milky mess, and both kegs were empty soon after data collection was done. This is a definite “make again” beer for me.

| DISCUSSION |

Of the various things brewers consider when it comes to making a tasty batch of beer, one that some have accepted as a non-issue is the amount of headspace present during fermentation. One of benefit of leaving a some space above the beer is that it reduces the risk of a messy blowoff, though some would contend this comes at the expense of increasing the chances of oxidation. With a prior xBmt supporting the claims of the concerned, the fact tasters in this xBmt were unable tell apart beers fermented under different amounts of headspace was somewhat unexpected.

In considering reasons these results don’t align with those from the original xBmt on headspace, it’s entirely possible the differences perceived by tasters in the first one were caused not by headspace, but rather actual volume of beer being fermented. However, if beer volume wasn’t at play, a reasonable explanation might be that the disparity in headspace amount between the batches in this xBmt wasn’t drastic enough to yield a perceptible difference– 4 gallons/15.1 liters in the first trial compared to 1.5 gallons/5.7 liters in this xBmt. Finally, it’s also possible whatever impact headspace has on beer is subtle enough to be unnoticeable in more characterful styles such as NEIPA.

As a matter of course, I leave just enough headspace to account for the kräusen that develops during fermentation, though resist leaving more than necessary. Seeing as the results from this xBmt contradict previous findings, I’m certainly not prepared to make any final conclusions, though I do feel comfortable continuing to ferment with the amount of headspace I always have. That said, I’m interested to continue exploring this variable in other situations in the hopes better understanding its impact on beer.

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

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