Author: Jake Huolihan

Hot side Aeration (HSA) is often cited as detrimental to long term stability of beer. It has been extensively studied at a professional level with results demonstrating that when wort is between 120°F-212°F/49°C-100°C, oxygen pickup can increase the concentration of oxidized fatty acids that are carried forward into the finished beer and cause off-flavors. HSA has been a focus of discussion and experimentation among homebrewers, with many ultimately choosing to view it as a myth, a brewing bogeyman that’s perhaps more an issue for larger scale commercial operations.

However, some brewers maintain their position that HSA does indeed have an impact, arguing that previous experiments designed to test the effects HSA has on beer were in some way flawed. Following publication of the first xBmt on HSA where participants were unable to reliably distinguish a high HSA beer from a low HSA beer, some people contended the non-significant results were due to the fact data was collected when the beer was fresh, that the off-flavors associated with HSA require time to develop.

I’ve personally stuck with trying to keep HSA to a minimum in my brewing because, well, better safe than sorry. Having never noticed much of a qualitative difference between my low HSA beers and those of other brewers I know who pay it no mind, I thought it would be useful to revisit the variable of HSA, this time focusing on how it effects beer over time.

| PURPOSE |

To evaluate the the differences between two beers of the same recipe aged for a period of 8 weeks where one was intentionally aerated at numerous points in the brewing process prior to the wort being chilled while the other was not.

| METHODS |

I was in the mood for a simple dark lager and thought it’d work well for this xBmt given the aging component.

Dark Lager Recipe

Recipe Details Batch Size Boil Time IBU SRM Est. OG Est. FG ABV 5.5 gal 60 min 28.5 IBUs 18.9 SRM 1.054 1.014 5.2 % Actuals 1.054 1.012 5.5 % Fermentables Name Amount % Pilsner (2 Row) Bel 9.75 lbs 86.67 Honey Malt 9 oz 5 Melanoiden Malt 9 oz 5 BlackPrinz 6 oz 3.33 Hops Name Amount Time Use Form Alpha % Nugget 11 g 60 min Boil Pellet 13 Saaz 29 g 30 min Boil Pellet 3.8 Yeast Name Lab Attenuation Temperature Saflager S-189 (S-189) Fermentis 74% 48.2°F - 71.6°F Notes Water Profile: Ca 7 | Mg 2 | Na 2 | SO4 5 | Cl 5 | HCO3 15 | pH 5.4

A day before brewing, I prepared a traditional viability starter of Saflager S-189 dry lager yeast to reach the cell count recommended by my preferred calculator.

Later that evening, I collected the proper volume of brewing water and adjusted it to my preferred profile in preparation for the following day’s brew. I awoke the following morning and immediately began heating my strike water.

As the liquor was coming to strike temperature, I measured out and milled my grains.

With the strike water slightly overheated, I transferred it to my converted cooler MLT, let it sit for a brief period to preheat, then mashed in once the water had dropped to the recommended strike temperature.

Rather than performing separate mashes, which could introduce extraneous variables, we decided it would be best to evenly split the sweet wort from a single mash prior to boiling then beat the shit out of one while treating the other like a frail kitten. During the 60 minute rest, I gently stirred the mash 3 times in 15 minute intervals, per my normal routine. Underletting the sparge water to reduce aeration as much as possible, I performed an otherwise standard batch sparge to collect the proper volume of sweet wort when the mash was complete.

With the entire volume of wort in a single kettle, I gently stirred to ensure homogenization, making sure not to splash it around, then transferred half to a second kettle.

As the wort was transferring, I began vigorously whipping the HSA half with a comically large wire whisk.

I did this throughout the duration of the transfer, which left my arm feeling like it was going to fall off. The temperature of the wort at this point was approximately 150°F/65°C. I staggered the start of each boil by 10 minutes, letting each roll for 60 minutes with hops added at the times stated in the recipe. I regularly beat the HSA batch throughout the boil at a rate of 1 minute every 20 minutes or so. Each wort was quickly chilled at the completion of their respective boil.

Hydrometer measurements at this point showed the HSA batch to be a couple SG points higher than the low HSA batch, which may very well be a function of something other than the variable of investigation, though I wondered if maybe the constant agitation of the HSA wort somehow led to increased evaporation.

I transferred equal amounts of wort from either kettle were transferred into fermentors that were then placed in my fermentation chamber to finish chilling. Both batches of wort had stabilized at my preferred fermentation temperature of 58°F/14°C by the following morning, so I decanted the starter then evenly split the yeast between each batch, hitting each with a 60 second dose of pure oxygen afterwards. I observed activity in the low HSA beer 12 hours after pitching yeast, while the HSA beer appeared to be lagging a bit.

Just over 24 hours later, both beers appeared to be fermenting along nicely.

I began gently raising the fermentation temperature at this point in hopes of encouraging complete attenuation, ultimately reaching a peak of 70°F/22°C a week or so later. Initial hydrometer readings at 2 weeks in revealed both beers had likely finished fermenting. I gave them another few days before confirming FG had indeed been reached.

The beers were cold crashed and fined with gelatin before being kegged in separate 2.5 gallon corny kegs that were placed in my keezer on gas and left alone for 8 weeks, which we reasoned was more than enough time for any negative effects of HSA to manifest. After the tedious wait, when the time came to present these beers to participants, both were gorgeously clear and carbonated.

| RESULTS |

A panel of 27 people with varying degrees of experience participated in this xBmt. Each taster, blind to the variable being investigated, was served 2 samples of the high HSA beer and 1 sample of the low HSA beer in different colored opaque cups then instructed to select the unique sample. Given the sample size, a total of 14 correct selections (p<0.05) would have been required to achieve statistical significance, while only 9 tasters (p=0.57) chose the different beer. These results indicate participants were unable to reliably distinguish a beer produced with intentionally high HSA from one made using low HSA methods after both were aged for 8 weeks.

My Impressions: I pulled my first samples of these beers during a brew day video chat with the other contributors and immediately remarked how different the high HSA sample was from the low HSA sample. In a non-blind side by side comparison, I boasted about how easy this was going to be for me, a longtime HSA fearing brewer, to distinguish. Then, during another video chat later that day, I confidently did my first “blind” triangle test. First whiff… crap, those are similar, no biggie though… second whiff… nope, hmm… first taste… what the hell… second taste following a palate cleansing sip of water… shit! I got it wrong, I simply couldn’t tell them apart, my desire to have my beliefs confirm apparently influencing my perception. Over 4 additional attempts, I was right only once, leaving me resigned to the likelihood that a perceptible difference didn’t exist.

Out of curiosity, I entered the high HSA beer into a great competition hosted by the Fermentologists homebrew club, it was 6 weeks old at the time. I didn’t really have a specific style in mind when I brewed the beer but figured it most resembled a a Baltic Porter, so I entered it as that. Lo and behold, it took gold in the category and came up just a tad short in the BOS round.

| DISCUSSION |

The results of this xBmt corroborates previous findings demonstrating the inability for tasters to distinguish a high HSA beer from a low HSA beer, even after a couple months of aging. While the growing mound of evidence really does seem to support the idea that HSA may not be as big of an issue as many of us thought, particularly on the homebrew scale, there are other possible explanations some have posited as to why we’re not experiencing the expected negative effects. For example, since cold storage tends to slow down reaction rates, there’s a chance the off-flavors associated with HSA are more quickly expressed when beer is stored at warmer temperatures. Another curious hypothesis, is that the ingress of oxygen at all points during the brewing process, from milling through packaging, is enough to essentially mitigate the effects of HSA alone.

Or, maybe it really isn’t that big of a deal. As difficult as this is for me to swallow, these results, combined with the fact I’ve had many delicious beers made by brewers who don’t concern themselves with limiting HSA, have left me feeling inclined to release my grip on the conventional wisdom. I won’t be whipping my wort on the hot-side or anything silly like that, but I’ll admit to feeling more relaxed knowing a little splashing during transfers won’t ruin my beer.

Finally, an interesting anecdote– I administered the triangle test to a professional brewer from a fairly well known local brewery and he happened to accurately select the unique sample. In discussing the xBmt with him after he finished the survey, I learned he had a strong preference for the high HSA beer, which surprised both of us seeing as he takes effort to reduce HSA in his own brewing. This reminded me of something I once heard Dr. Charlie Bamforth say during an interview:

When you talk about flavor stability, you quickly, if you’re not careful, go into the realm of philosophy about what is right and what is wrong.

Such a poignant observation!

Feel free to share your thoughts on hot-side aeration and how it is potentially impacted by age in the comments section below!

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