Author: Jake Huolihan

While brewers yeast can and will ferment anaerobically, a key component in promoting healthy fermentation and quality beer is oxygen. When pitched into wort, yeast rapidly absorbs oxygen for cell membrane synthesis, which encourages the production of sterols and unsaturated fatty acids necessary for cell growth, ultimately improving viability.

A common practice for many commercial breweries involves reusing the yeast from one batch to ferment another, a process that can be repeated over numerous generations. Pure oxygen is often used to dose the wort in such situations in order to ensure the healthiest yeast for future batches. For homebrewers who rely primarily on fresh pitches of yeast, oxygenation may not be as crucial, in fact a couple past xBmts seem to suggest it has little if any benefit. But what about in less favorable conditions?

I’ve bought into the benefit of oxygenation and dose every batch I made with pure oxygen with the belief it helps me produce the best beer possible. However, I’m aware of many who skip this step and have great results. With the growing popularity among homebrewers of harvesting and reusing yeast, I was curious how oxygenation might impact a high OG beer pitched with previously used yeast and put it to the test!

| PURPOSE |

To evaluated the differences between 2 high OG beers fermented with previously used yeast where one was dosed with pure oxygen and the other was not.

| METHODS |

Having harvested some Imperial Yeast B48 Triple Double from a recent batch, I designed a Belgian Quad for this xBmt.

Gasp

Recipe Details Batch Size Boil Time IBU SRM Est. OG Est. FG ABV 5.5 gal 60 min 39.0 IBUs 22.2 SRM 1.089 1.015 10.0 % Actuals 1.089 1.014 10.1 % Fermentables Name Amount % Odyssey Pilsner 19 lbs 88.37 Candi Sugar, Amber 2 lbs 9.3 Candi Sugar, Dark 8 oz 2.33 Hops Name Amount Time Use Form Alpha % Loral 20 g 60 min Boil Pellet 10.3 Loral 30 g 15 min Boil Pellet 10.3 Yeast Name Lab Attenuation Temperature Triple Double (B48) Imperial Yeast 76% 65°F - 77°F Notes Water Profile: Ca 65 | Mg 0 | Na 8 | SO4 67 | Cl 68 Download Download this recipe's BeerXML file

The night before brewing, I collected RO water and adjusted it to my desired profile.

I then weighed out and milled the grains.

When I woke up the next morning, I turned on the elements to heat my strike water then proceeded to weigh out the kettle hop additions. When the water was slightly warmer than strike temperature, I transferred it to my mash tun, gave it a few minutes to preheat, then mashed in to hit my target temperature.

The mash was left to rest for 60 minutes with intermittent stirring.

Once the mash was complete, I collected the sweet wort in my kettle and brought it up to a boil.

Following a 60 minute boil, I turned the element off and quickly chilled the wort.

A refractometer reading showed the wort was at a respectable 1.073 OG.

I then gently racked equal volumes of wort to separate Brew Buckets, being careful not to aerate it during the transfer process.

The fermentors were connected to my glycol chiller and rapidly cooled to my desired fermentation temperature of 66°F/19°C. At this point, I took a jar of Imperial Yeast B48 Triple Double I’d harvested from a batch 2 days prior, split it between a couple sanitized mason jars to ensure each wort received the same amount, then pitched one jar into either batch.

I proceeded to dose one of the beers with pure oxygen for 3 minutes while the other was left alone.

After 2 days of fermentation, I added equal amounts of Belgian Candi Syrup to each beer.

With signs of fermentation activity absent in both batches 13 days post-pitch, I took hydrometer measurments showing both had finished at a dangerously low 1.014 FG.

The beers were kegged.

The beers were left to cold condition and carbonate in my keezer. With its higher ABV, I left these ones alone a little longer than usual and noticed a slight difference in clarity after about a month in the keg.

When it came time to serve these beers to participants, the difference in clarity didn’t seem as stark, but was still present.

| RESULTS |

A total of 25 people of varying levels of experience participated in this xBmt. Each participant was served 1 sample of the oxygenated beer and 2 samples of the beer that was not oxygenated in different colored opaque cups then asked to identify the unique sample. While 13 tasters (p<0.05) would have had to accurately identify the unique sample in order to reach statistical significance, only 4 (p=0.99) did so, indicating participants in this xBmt were unable to reliably distinguish a beer whose wort was dosed with pure oxygen from one that wasn’t oxygenated when both were fermented with yeast harvested from a prior batch. For the curious, the two similar samples were selected by 10 and 11 participants.

My Impressions: Out of the 3 triangle tests I attempted, I identified the odd-beer-out 0 times, they smelled and tasted identical to me, which I did not expect. Both beers were fantastic, in fact they ended up doing quite well in a couple competitions I entered them in.

| DISCUSSION |

The role oxygen plays in the life cycle of yeast is well known and its impact on certain observable factors has been noted by many, making the slight difference in appearance between the beers in this xBmt not too surprising. Interestingly, though, whatever it was that led to the difference in appearance wasn’t enough to impact other characteristics, as blind participants were unable to tell apart the beer whose wort was dosed with oxygen from the one that wasn’t aerated, despite being fermented with second generation yeast.

Viewed in light of the results from past xBmts on the same variable, these findings add to the evidence suggesting wort oxygenation doesn’t have the impact on beer aroma, flavor, and mouthfeel as many believe. One possible explanation for these results could be that these xBmts have been completed on the homebrew scale and that results might differ in larger scale conditions, which may very well be true. However, many homebrewers fervently adhere to the practice of oxygenation under the belief it improves the quality of their beer, and these results yet again call this into question. Is it really worth it?

For me, it is. While these results have definitely left me feeling less compelled to advocate for oxygenation to others, I’ll continue to do it for most of my beers. Not only do I appreciate the impact it has on clarity, which I’ve observed in more than just this xBmt, but because I view it as a relatively cheap and easy way to insure against things potentially going awry. Also, I have the equipment, may as well use it…

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

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