Aerating hot wort can cause oxidation. Oxidation causes long term off flavors that do not age out. I believe the taste associated with oxidation is somewhat like wet cardboard.
That's another one of those things that's blown waaaay out of proportion. It's one of those worst case scenarios that Palmer stuck in his book and every noob on the planet took as cannon and started repeated.
You'll find that many of us who use immersion chillers begin stirring the wort immediately as well as moving it up and down and creating quite a bit of o2 in there. And our beers turn out fine, not instantocardboard or whatever you hide under your bunks laying awake night worrying about.
HSA for homebrewers is waaaayyyyy paranoia...another thing that made the leap from commercial breweries of tastless lager that has to have a long shelf life and absolutely no flavor (good or bad) otherwise.
Hot-side aeration may be demonstrated in medium and large commercial breweries because the brewing equipment is so big that splashing is a really dramatic event. Think of liquid flowing through a six-inch pipe at 400 gallons per minute and cascading 12 feet through the air before hitting the bottom of a tank. (Maybe, see video below.)
But to the home brewer it's only a bogeyman....
I love the quote about the Basic Brewing experiments on Maltybrew.com
Hot-side aeration
myth?
I listened to a great podcast from Basic Brewing Radio yesterday on hot-side aeration. Everyone seems to debate whether or not this is a concern for homebrewing. The podcast covers an experiment done by some homebrewers in Austin where they try hard to cause HSA in a small batch.
I was never too concerned about HSA in my brewing and now I think Im even less concerned.
FYI, here are the basic brewing podcasts on it...
March 16, 2006 - Hot Side Aeration
Charles, Chris, James and BrianWe travel to Austin Homebrew Supply in Austin, Texas to taste the results of Brian Warren's experiment in Hot Side Aeration. The experiment produced some very surprising and interesting results.
Click to listen
June 22, 2006 - Two Homebrew Experiments
froth_sm.jpgWe hear from two homebrew experiments: William Tope, a high school student from Houston, Texas, delves into whether alpha acid levels of hops affect fermentation rates, and the Hot Side Aeration experiment continues with Brian Warren and John Holder.
Click to listen
November 2, 2006 - HSA Experiment: Final Chapter
Andy Sparks and James Spencer join Brian Warren and John Holder in Denver to taste the last round of samples in the Hot Side Aeration experiment. We also get feedback about the experiment from John Palmer.
Click to listen
Most of those who "claim" it are brand new brewers who "think" they know somethings wrong with their beer when it usually it's just green beer, and later when they taste their beer again, weeks late they usually come back and say the beer is fine. An equal number have blamed an off flavor on diactly or even autolysis, until we point out certain facts about those different things, and again a few weeks later they usually post their embarrassment at being so freaked out back then.
We're not saying you don't practice good brewing techniques, of any types, just that most of those things that new brewers panic about, that they read about in books is worst case scenario stuff, misunderstood conjecture that has been handed down over the years as "canon" with little or no validity, something that is of more worry to commercial operations or lager breweries, or myths that have been disproven in light of modern brewing science, that was based on OLD brewing info.
And in reality our beer is a lot more resililiant than most new brewers believe, because at their stage of brewing they understand just enough to be dangerous.
It takes a lot of abuse to ruin our beer...and even the "day to day" mistakes that we make is often NOT enough to ruin our beer. Its pretty hardy stuff.
If you read the stories in here, of "mistakes" that people have made here, you will come to realize that a lot of stuff happens in the normal course of brewing, and the beer still manages to survive, so if you make a mistake, you don't need to immedietly panic and assume your beer is ruined.....
https://www.homebrewtalk.com/f39/wh...where-your-beer-still-turned-out-great-96780/
And a lot of stuff can be corrected with time anyway.
https://www.homebrewtalk.com/f39/ne...virtue-time-heals-all-things-even-beer-73254/
In years of brewing and in helping panic new brewers I've yet to find cases where it wasn't a false alarm in just about anything any new brewer has claimed, and that is the case for the dreaded HSA, Autolysis, and 99.95% of the new brewer infection threads as well.
I'll save you the bother of searching, but here's a few of those new brewer HSA panic threads...
https://www.homebrewtalk.com/f36/hot-side-aeration-so-im-idiot-71873/
https://www.homebrewtalk.com/f12/who-afraid-hsa-76779/
https://www.homebrewtalk.com/f13/hot-side-aeration-71806/
HSA is something that get's discussed by commercial brewers in journals, and some overzealous homebrewer then starts worrying about it, and it get spread into the HOBBY community, with little understanding...and then people brewing thier first beer start threads worrying about it...
So don't sweat your new brewer head about HSA....or anything, you beer is much hardier than you think...
And if you still are worried, then watch this video of a commercial brewhouse...
You think they are concerned about HSA?
The only time we have to be concerned with oxygenating and getting liquid cardboard is when fermentation has started. Oxygen + Fermented Beer = Liquid Cardboard.
Man, we haven't had an HSA believer on here in a couple years...thought that one was dead and buried.