Sunday, January 29, 2012

Oxidation in Beers

I'll admit I had a flavor problem that I had a difficult time tracing, and it ended up being oxidation. This article will describe how I arrived at the conclusion that oxygen was to blame, and also how I addressed the issue.

The curious thing about the off-flavor was that my beer tasted perfect when primary fermentation was done, when I transferred to secondary, when I transferred to the keg, and probably 2-3 weeks after that. However, as the beer aged, it took on tastes similar to sherry or cough syrup...regardless of the style of beer.

John Palmer writes about off-flavors in his How To Brew publication (see section 21.2), and this helped confirm the flavor. Additionally, a couple friends offered advice on how to diagnose and address it. I'll admit I was somewhat lax when it came to preventing oxidation, so I took the following steps:
  • When I transfer beer to the secondary, I purge the secondary vessel with CO2, and siphon slowly, all while flowing CO2 gently.
  • When transferring to the keg, I follow the same procedure: flowing CO2 into the keg during transfer.
It doesn't hurt to make a few other changes that were probably overdue, or just good practice, so I also did these:
  • Replaced all beverage and siphon tubing.
  • Ran PBW through by counterflow chiller multiple times, and let it sit for a while, too.
  • Ferment in glass (I will be avoiding white food grade plastic, as it is not impermeable to oxygen, and also can take on flavors).
  • Use only the refractometer Santa gave me from now on.
  • Watch my sparge temperatures more carefully.
So far, the chocolate coffee oatmeal stout I made has passed the 4 week mark, so I'm pretty confident the problem was either solely oxidation, or oxidation plus old serving/siphon lines. If you notice a sherry-like or cough syrup taste (I never got the cardboard taste many describe), you may have the same issue that plagued a few of my beers. It is a terrible waste to spend all the time, effort, and money on great beer, and have it spoil!

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