Author: Marshall Schott

There has been a lot of talk over the last few years about whether or not hot-side aeration (HSA) is something homebrewers should worry about, with many folks emphatically tossing it into the seemingly ever growing pile of brewing myths. And everybody seems to have something to say about it!

In what is arguably the most trusted and popular book on homebrewing, How To Brew, John Palmer cautions:

“You should not aerate when the wort is hot, or even warm. Aeration of hot wort will cause the oxygen to chemically bind to various wort compounds. Over time, these compounds will break down, freeing atomic oxygen back into the beer where it can oxidize the alcohols and hop compounds producing off-flavors and aromas like wet cardboard or sherry-like flavors.” (6.9.3)

He again brings up the perils of HSA in the Starting the Mash section, explaining, “Hot side aeration can occur anytime the wort is hotter than 80°F. Oxidation of wort compounds will not be affected by the subsequent boil, and will cause flavor stability problems later.” This seems to suggest that a gentle hand should be used at all steps in the brewing process that come prior to the wort being chilled.

Another brewing badass, Randy Mosher, in his fantastic book, Radical Brewing, makes the following observation:

“[HSA] has been a bit of a bogeyman of late, with some people going to extreme lengths to prevent it. The question is, will it cause problems in homebrewed beer, especially oxidized flavors as the beer ages? Breweries certainly take it seriously, but then they have a lot more to worry about in terms of product stability. The jury is still out as to whether HSA is injurious to your average batch of homebrew, but I think it’s safe to say it isn’t a huge problem, a view supported by the fact that the phenomenon was not even discovered by brewing science until fairly recently. But it also makes sense to try to avoid techniques that are likely to expose hot wort to an undue amount of air if alternative methods can be found.”

So, Pascal’s wager for homebrewers. Cool. A couple years ago, I decided to stop caring so much about HSA in my own brewing and didn’t really notice any degradation in the flavor or stability of my homemade beer. Then about a year ago, I watched a speech by John Kimmich of The Alchemist in which he said HSA is “just terrible, you can’t do that to wort” (34:55). This dude makes Heady Topper, one of the highest rated beers in the world, surely what he has to say should be taken seriously. It wasn’t but a few months later that I listened to an interview with Charlie Bamforth, professor of brewing science at UC Davis and purported King of Foam, in which he claimed, in essence, that HSA does impact the wort, just not to a significant enough degree to make a noticeable difference. He went on to say there are far more important factors brewers should focus on such as pitching healthy yeast and ensuring minimal oxygen exposure at packaging.

While I’ve been pleased with my own lack of care on this issue, the time finally came to put it to the test. Not only because I remain curious, but also because I’ve received more requests to perform this exBEERiment than any other… by a long shot. So, here you go!

| PURPOSE |

To evaluate the impact hot-side aeration has on all characteristics of a beer when compared to a non-aerated batch of the same recipe.

| METHOD

I originally planned on splitting a 10 gallon batch into 2 kettles following collection of sweet wort from the MLT, after which one would be beat to holy hell while the other would be treated like a newborn baby. However, in order to really test the extremes of HSA, I decided it would be best to produce 2 batches of the same beer using separate mashes, as this would allow me to treat both differently at all points throughout the process. I settled on my Hop Test Bitter for this exBEERiment, making some minor changes from the original recipe:

Grist

7.0 lbs Maris Otter (80 %)

1.0 lbs Crystal 10 (11.4 %)

8.0 oz Victory Malt (5.3 %)

4.0 oz Crystal 60 (3.2 %)

Hops

~8 IBU Falconer’s Flight – First Wort Hop (FWH)

15.00 g Willamette – Boil 20.0 min

15.00 g Falconer’s Flight – Boil 10.0 min

21.00 g Falconer’s Flight – Boil 5.0 min

21.00 g Falconer’s Flight – Flameout w/ 10 min steep



Yeast

1.0 pkg WLP002 – English Ale Yeast

This is a beer I prefer to use the No Sparge mashing method for, as it supposedly produces a more malty beer. For the no HSA batch, the hot liquor was treated very gently and transferred to the my MLT using a 1 gallon aluminum pitcher to reduce the chances of aeration. I then stirred with ease as the grain was added, which still produced some foaming.

For the HSA mash, I used my 24″ wire whisk to whip the living crap out of the hot liquor, transferred it to the MLT with vigor, then used the same whisk to integrate the grain with the liquor.

Per my usual routine, both mashes were stirred briefly twice during the 1 hour saccharification rest, the non-HSA batch being stirred lightly with a long plastic spoon while the HSA batch was whipped vigorously. When it came time to collect the wort, I attached a hose to my MLT, ran off directly into my 14.5 gallon kettle, then moved the kettle to the burner.

When it came time to collect the runnings for the HSA batch, I simply opened the valve on the MLT, let it drain haphazardly into an old 6 gallon fermentation bucket, then I poured the wort into the kettle with plenty of splashing.

As if that weren’t enough, I used a whisk to whip the wort multiple times throughout the boil (twice per every 10 minute increment, 12 times altogether).

Wanting to go beyond just the strength of my own wrist and forearm, I employed the use of a paint stirrer attached to a drill.

This sent wort flying everywhere, so I only did it a couple times during the boil. The pre-boil and post-boil OG readings for each batch were the same, this felt nice.

Both worts were chilled in no time using my trusty King Cobra IC.

While I usually engage in chilling practices that do aerate the wort while it is still hot, I was deliberately gentle with the no HSA batch and only began moving the IC around once the temp was below 80°F. The HSA batch got the regular treatment. Both worts were oxygenated using a plastic spray aerator while being transferred to 6 gallon plastic carboys, then they were placed in a cool fermentation chamber to finish chilling to my target pitch temp of 64°F, after which both were pitched with an equal sized starter of WLP002 English Ale Yeast.

I was curious if there’d be any differences in fermentation activity betwen the beers and had a sort of preconceived assumption the HSA batch might have less lag due to all the extra aeration. Things were definitely looking different just 2 hours post-pitch.

About 3 hours later, a mere 5 hours since pitching the yeast, the HSA beer had developed a layer of something (not sure if it was krausen or not) that nearly covered the top of the beer; the no HSA had zero signs of activity, which is more in line with what I usually see at this point.

By 16 hours post-pitch, both beers had fully developed krausens and they were starting to look a bit more similar.

A side-view after a full day since pitching yeast revealed a rather drastic difference in color.

I figured this was likely due to the fact the HSA beer started before the no HSA beer, as it took on a similar color a day later.

Using my ale fermentation profile in The Black Box controller, the temp began ramping up once active fermentation slowed down. The beers looked mostly similar at this point.

Just prior to cold crashing, I took samples of both beers to measure the FG. The HSA batch appeared to have dropped about .001 more point than the no HSA batch.

The beers were cold crashed for a couple days then I used the sterile siphon starter to keg them up per my usual method.

After sitting in kegs in my keezer for about a week, the beers were ready to be evaluated.

| RESULTS |

A panel of 12 tasters, all blind to the nature of the exBEERiment, were asked to complete a triangle test in a setting relatively free from distractions. Of the 3 samples the tasters received, 2 were the HSA beer and one was the no HSA beer, they were instructed to try to distinguish the one that was different from the others. Those tasters who correctly selected the beer that was different were then asked to proceed to a survey comparing the 2 different beers, knowing only that the beers they were evaluating were somehow different.

Given a sample size of 12 participants, 8 would have had to correctly identify the different beer to imply significance (p<.05). For this exBEERiment, only 4 people correctly identified the no HSA beer as being different from the others, which statistically speaking, is exactly what we might expect to occur purely by chance. This conclusion is supported by the fact that the 4 tasters who moved on to complete the comparison survey provided inconsistent responses with nothing even remotely in the way of meaningful interpretations. For example, after the nature of the exBEERiment was revealed in a question at the end of the second survey, the tasters were asked to select the one they thought was HSA- each of the 2 responses was selected by 2 tasters (50%).

My impressions: From the FG samples I took over a month prior to writing this article to the comparison I did 3 days ago, I’ve never perceived a lick of difference between the no HSA and HSA beers, everything about them is exactly the same to me. They are equal in terms of appearance, flavor, aroma, and mouthfeel. Even the slightly higher ABV of the HSA beer didn’t seem to have an impact on perceived differences. Now, as far as the minor changes I made to the Hop Test Bitter recipe, well, let’s just say I’ll be sticking with the original grain bill henceforth.

| DISCUSSION |

The results of this exBEERiment corroborate the findings from other experiments on the same topic. I exerted more effort aerating the mash and wort than I’ve ever exerted trying to limit hot-side aeration, and even so, there seemed to be absolutely no detriment to the quality of the finished beer. While I’ve touted the whole “HSA is myth” thing in the past, I’ll admit I was likely engaging in confirmation bias, simply seeking evidence to support my practices. However, the growing amount of evidence supports the notion that HSA, while perhaps not necessarily mythical, does not have a noticeable negative impact on homebrewed beer and hence can be appropriately relegated to the annals of homebrew history.

If you have any questions or concerns, please do not hesitate to voice them in the comments section below. Cheers!

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