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Old 04-06-2006, 04:23 PM   #1
Feb 2006
Posts: 901
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Prior to coming to this forum, I was not aware that aeration was a bad thing at certain stages of the brewing process. In other words, I never worried about avoiding it when racking my beers to secondary. Since this is the case, I've never really experienced (knowingly) the ill effects of such practices.

So, what are the negative effects of hot and cold side aeration? Answers in both practical and scientific terms will be much appreciated.

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Old 04-06-2006, 11:04 PM   #2
david_42's Avatar
Oct 2005
Oak Grove, Oregon, USA
Posts: 25,599
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Cold side aeration is good, yeast need oxygen to grow.

Hot side (over 80F) causes oxidation which results in long term flavor stability problems. The Beer Wizard on HSA All it comes down to for the homebrewer is, "Don't splash hot wort or mash".

Then there's the exposure inherent in decoction mashing and batch sparging.

I think the key words are "long term", which is probably an interval much longer than the life expectancy of a case of homebrew.
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Old 04-07-2006, 12:09 AM   #3
Mar 2005
Alexandria, VA
Posts: 556
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Originally Posted by david_42
Cold side aeration is good, yeast need oxygen to grow.
Initially this is true, but after the yeast is pitched, cold side aeration is BAD. It can easily cause off-flavors. Of course, if you like the taste of wet carboard mixed with beer, aerate away.....

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Old 04-07-2006, 04:33 AM   #4
Aug 2005
Tampa, FL
Posts: 606
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The common scientific answer is this:

aerating the wort whether hot or cold anytime other than just before pitching the yeast (and the wort should be under 80F at this point) is bad. You dissolve oxygen into the solution and oxygen does what it does best - oxidizes various wort compounds and the end result can be stale/'cardboardy' tasting beer. The off taste usually takes a while to show up - so it's less of a concern if you drink the beer quickly but if you keep the beer for a while then you'll probably experience "long term flavor instability" - the beer will go bad. Yes, it'll still be drinkable but probably won't taste very good..

Personally, I don't worry as much about aeration as I used to.. I have yet to experience stale homebrew and I have been drinking a few bottles recently that are 8 months old (quite tasty btw). Others are fanatical about aeration (like sanitation)..

Point is, try to avoid aerating, splashing, pouring, etc. your wort but don't get obsessive about it.

This advice is worth exactly what you payed for it.

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Old 04-07-2006, 10:43 AM   #5
boo boo
Jun 2005
Hearts's Delight, Newfoundland
Posts: 4,165
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Really, the only time o2 should get into your wort is just before pitching your yeast. You can avoid aerating your wort by not splashing the beer or letting it run down the side of buckets and other equipment. Keep the end of your siphon hose under your wort when siphoning.
I too was like yourself and didn't consider aeration while I was splashing my beer into my bottling bucket, making all that nice foam. The end effect was a beer that could have tasted better if it were racked more carefully.
On the hot side, o2 attaches itself to molecules in the wort and don't come out before changing the structure of the wort, causing potential beer spoiling. I'm not too scientific about it and if you google hot side aeration I'm sure you will have a lot of reading to do.
Basicially what Lost said is true.

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