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Hot Side Aeration

I have a copy of the Zymurgy “Best Articles” book. It’s sort of like a greatest hits album of all the articles from Zymurgy. (For those who are unfamiliar with this publication, it’s the magazine that accompanies your membership to the AHA) It’s a little dated (published in 1998) but there are a few good reads in there, including the one on hot side aeration

I read an article last night written by the late George Fix about hot side aeration (HSA). HSA is the introduction of oxygen (in the form of air) into your hot wort. The presence of excess O2 in your hot wort leads to the oxidation of melanoidins in your wort. These oxidized molecules contribute to staling in your beer post packaging. The more of these there are the sooner your beer will become stale.

I have never worried too much about HSA because: 1. I don’t stir my wort much post boil. 2. I chill with an immersion wort chiller prior to racking the wort to my fermentor.

I always thought the biggest chance of HSA was during these later stages of wort handling, and when the wort is super hot still, i.e. above mash temps. However, Fix states that he believes that HSA happens at temperatures starting at around 86F!


His article warns about over-stirring your mash, splashing the runoff too much, and over- stirring the wort during boiling (at least I already knew that was bad). I know there is a lot of debate about HSA and whether it really happens with much ease or if you really need to work to get it to be a problem. Personal experience tells me that my process is not harmed much by HSA because I don’t really have much staling in my beers. At least I don’t think I do…

On the other hand, I will tell you something about my process that has me concerned now that I have read this HSA article. I am a batch sparger as I have said in previous posts. I collect my wort in white buckets as I run off from the mash tun. I have my kettle sitting up on my propane burner when I start. I transfer the wort from the bucket to the kettle by simply pouring it into the kettle…. It splashes a lot when I pour it, and this wort is at 168F. Then I start heating that wort while I collect my next running of wort from the tun. I dump that wort right into the kettle (wort from the bucket is at 168F, the wort in the kettle by now is near 200F) and I have more splashing.

Now like I said, I don’t think I have much in the way of stale flavors in my beers, but Fix was a smart guy and well respected. I do sometimes have a flavor component in my beer that I can’t identify, maybe it is a mild oxidation leading to HSA products in the wort prior to boiling.

What to do…

Well, Fix recommends making the same wort twice. He recommends that you really abuse the first one (stir the mash excessively, pour in the sparge water aggressively, perform a messy vourlaf, stir the wort several times during the boil, splash the wort around prior to cooling). He then recommends taking as much care as you can with the second wort to not introduce any HSA (this may just be doing your regular process), but with a little more care. I like this approach. Using two test batches one that is as close to your normal process as possible, the second… work hard at making the system fail.

Fix says that after you ferment those beers out and bottle them you may then realize how HSA effects your final product. This seems like a strange thing to do, and who wants to potentially ruin 5 gallons of brew?  But this is something to consider. I certainly will have to rethink my transfer method. Next time I may actually collect my running in my bottling bucket and use a hose from the spigot to the base of the kettle to transfer the wort.


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  1. TylerC

    I used to be a batch sparger with the same method of hot wort transfer as described in this article. Recently, at the NHC, I received the oxidized comment on at least two of my beers. Also, after brewing an incredible porter, its flavor has begun to degrade and stale, and it’s only been a few months. I’m not attempting to minimize everything that could stale beer in my process (I’ve stopped using a racking cane, I no longer ferment with carboy hoods [maybe more oxygen permeable than rubber stoppers(?)], etc) Also, I’m now fly sparging. What I can say for this method is (a) I no longer have to pick up a heavy bucket, (b) My efficiency has gone up by roughly 2% (still more experimentation to do with that), and (c) I’ve never had fermentations this active (and, yes, they’re all temp controlled and always have been by a dedicated chest freezer [perhaps this supports the conclusions of the recent BYO article on batch vs. fly sparging to some extent]). I’ve brewed a few lagers and a pale ale with this new method. Since I’ve started brewing with this method none of my fermentations have completed yet ( I’ve got another week or so) ; however, I remain confident that there will be a positive effect on long term flavor stability. I may post back here in a few months if I can remember that I ever had a problem by then 😉

  2. Booker Payamps

    Great post, thanks lots!

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