Hot-side aeration (HSA) is the introduction of oxygen to wort during "hot side" operations such as mashing, lautering, boiling and whirlpool. Prior evidence indicated that hot-side aeration harms the shelf-life of beer by increasing the concentration of oxidized fatty acids. However, there is an emerging body of evidence contradicting these claims.

What is the prevailing evidence regarding HSA?


Oh boy this will be a fun question.

I draw my line in the sand at the point of the boil. The way my equipment is set up I collect my mash run off in a spare bucket. I then pour it into my keg/kettle and start the heat. Meanwhile I start the second run off into the now empty bucket (yes I am a batch sparger). The wort is ~168-170F.

I can honestly say that I have never seen this cause premature oxidation in my beer and the 6-8 different fellow brewers that sample my beer have never mentioned it. Nor does it come up in competition scoresheets. Furthermore, I don't drink my beer all that fast, so I have had beer sitting around for 4-6months, still not evidence of HSA from this preboil practice.

I have intentionally stirred the living daylights out of a small (2.5 gallon batch) and shot a little pure O2 into some wort post boil but pre chill. That batch was drinkable for the first couple weeks, but when stored at room temp in a keg for 3 weeks or so it started to get papery and oxidized. It was a amberish ale. 1.048OG.

So in my experience, the boil does tend to drive off the O2 that I may introduce from the violent pour into the kettle. OR the 168F just doesn't create those HSA reactions that fast.

OK that where I stand.


I have not come across any literature that encourages saturating your wort with more air than it is already exposed to during the brewing process. The increase presence of oxygen before your boil will cause lipid oxidation and this will affect the flavor stability of your ale or lager. With that being said, brewing is an art, and it seems we can never maximize one aspect of an operation to its full potential without compromising something else.

During milling, if you rely on a finer ground malt to increase your extraction of fermentable sugars, you will get more alcohol, but you will also increase the surface area of your mash and risk exposing the wort produced. If you stir continuously throughout a mash in an open tun or allow your bed to run dry during sparging, cloudier wort will be the result. Brewers disagree over whether clean or dirtier wort is better for fermentation, so this could be incredibly important to you or not. Oxidation risks are also increased depending on the raw materials you use. Rice adjuncts are going to be a lot less prone to LOX formation than corn, but can you afford the increased costs.

During mashing 15% of your malt lipids will become oxidized naturally, every thing I have ever read stresses that this percentage should be kept to a minimum, but since oxidation occurs no matter what you do, I can see where contrary evidence could come from. The most extensive overview I have found is Brewing Chemistry and Technology in the Americas. This book includes a fish scale diagram that will keep you cross-eyed for days, but once you are finished reading, it makes for a very useful door jam or nifty paper weight.

  • 2
    "...but you will also increase the surface area of your mash and risk exposing the wort produced." What?
    – brewchez
    Feb 24 '10 at 13:04

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