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Author Topic: Hot Side Aeration  (Read 921 times)

arrogantbastardale

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Hot Side Aeration
« on: September 20, 2012, 08:20:38 pm »
One of the most prevalent myths of homebrewing is Hot Side Aeration.  HSA is the effect of O2 oxidizing your wort at hot temperatures, and is caused by agitating the hot wort.  The more agitation and splashing, the more HSA will supposedly occur.  HSA off flavors include musty, cardboard, or paper aromas/flavors.  It is traditionally thought that the time period between the end of the boil and when chilled is when HSA can occur (I am not sure at which temperature the classic literature says that HSA is no longer an issue, but one old Zymurgy article says 86 degrees F!).  There have also been claims that too much agitation of the mash can cause HSA, although most information these days says that the boil will reverse any HSA in the mash.  From what I understand, beer oxidizes naturally, but at higher temperatures it oxidizes much easier due to the increase in energy (heat = energy).  That is why we store our beer long term in the fridge.

Introducing Dr. Charlie Bamforth, one of the leading brew scientists at UC Davis.  He has done a lot of research on behalf of Anheuser-Busch, including research on HSA.  He says that HSA, while not a complete myth, is something that professional brewers and especially homebrewers shouldn't worry about.  First of all the small scale at which homebrewers brew produces such a smaller amount of splashing in comparison to prouction breweries.  In addition with a healthy fermentation the yeast will clean up any effects of HSA. 

For more details, check out this interview with Dr. Bamforth.  It is one of the best episodes of the Brew Strong podcast: http://www.thebrewingnetwork.com/membersarchive/bs_hsa1-26-09.mp3
« Last Edit: September 20, 2012, 08:24:30 pm by arrogantbastardale »

Tony_G

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Re: Hot Side Aeration
« Reply #1 on: September 21, 2012, 11:24:56 am »
I guess oxidation, like any other chemical reaction, will happen faster at higher temps. I would think that while the wort is boiling, you're actually driving off disolved gasses so it make sense that the time to avoid excessive agitation would be when the wort is still hot but below the boiling point. The thing is, in normal homebrew process you're not spending much time in that temp. zone. I don't see a lot of agitating happening in the danger zone but it could be a reason to be careful until the wort cools. Anyway, it would be fairly easy to test this. Just pull a gallon of fresh hot wort, oxidize the heck out of with an airstone and O2 and then ferment under the same conditions as the main batch. If the test batch comes through that with no off flavors then I think it would be safe to put this one to bed. I'm hoping it tastes better and everyone goes "huh?"


arrogantbastardale

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Re: Hot Side Aeration
« Reply #2 on: September 21, 2012, 02:12:43 pm »
I guess oxidation, like any other chemical reaction, will happen faster at higher temps. I would think that while the wort is boiling, you're actually driving off disolved gasses so it make sense that the time to avoid excessive agitation would be when the wort is still hot but below the boiling point. The thing is, in normal homebrew process you're not spending much time in that temp. zone. I don't see a lot of agitating happening in the danger zone but it could be a reason to be careful until the wort cools. Anyway, it would be fairly easy to test this. Just pull a gallon of fresh hot wort, oxidize the heck out of with an airstone and O2 and then ferment under the same conditions as the main batch. If the test batch comes through that with no off flavors then I think it would be safe to put this one to bed. I'm hoping it tastes better and everyone goes "huh?"


BasicBrewing Radio did this exact thing with a whisk a few years prior to the Bamforth interview. They had some very interesting results! :)

http://ec.libsyn.com/p/0/d/5/0d5c47b44b7088b2/bbr11-02-06.mp3?d13a76d516d9dec20c3d276ce028ed5089ab1ce3dae902ea1d01cc8f35d4c95e3cc1&c_id=1452080

Mainiac

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Re: Hot Side Aeration
« Reply #3 on: September 21, 2012, 07:39:50 pm »
Bravo.  this is a great start

Tony_G

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Re: Hot Side Aeration
« Reply #4 on: September 21, 2012, 11:09:31 pm »
Very interesting recording in that now we know what not to do as far as an experiment goes. I found it pretty informative that some brewers are adding a Campdem tablet or other anti-oxidants to the mash, that adds some weight to the idea that it's the 100F to 130F temp range where the O2 binding enzyme becomes active.

 

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