“Oxidation flavors in finished beer are the product of the combined effect of dissolved oxygen, time, and temperature”

Oxidation flavors in finished beer are the product of the combined effect of [dissolved oxygen] DO, time, and temperature. An excess of any of these three oxidative factors can render a wonderful beer undrinkable. The volatility of fresh beer flavors coupled with the popularity of session IPA’s, juicy northwest style IPA’s, and west coast IPA’s getting lighter in body by the day, has made our friend oxygen public enemy number one for brewers, distributors, retailers, and consumers alike. Trans-2-nonenal, the chemical compound responsible for that classic cardboard oxidation taste is not the only problem than can arise when packaged beer has DO problems. Beer, in the presence of oxygen and warm temperatures can lose hop aroma, gain perceived sweetness, promote bacterial infection, create diacetyl (rancid butterscotch) and even change color. A super light colored lPA may be more of an amber color months later if not packaged and stored correctly.

The only way to deal with oxygen in warm beer is to have a continued fermentation within the package so the yeast will scavenge any remaining oxygen in solution. This technique is called bottle conditioning or keg conditioning and is the technique employed in the famed Sierra Nevada Pale Ale. Warmer temperatures stimulate the yeast to metabolize more oxygen, but as discussed earlier, simultaneously, the oxidative effects on the malts and hops is exacerbated at warmer temps. This is a classic pick your poison type of decision and world class beers have been made with and without bottle/keg conditioning. I have often wondered how some Belgian lambics can remain light in color after years of room temperature barrel aging while some American Pale Ales turn amber within months. I now believe it is the continued miracle of fermentation activity in the barrels that has protected the delicate beer from the onslaught of oxidative mayhem.

The only other option for breweries, and probably the most effective is to do their best to mitigate the big three oxidative factors of DO, time, and temp. This feat is easier said than done but can be accomplished through quality fermentation, minimal beer movement, closed transfer systems, cold storage, packaging date codes, and quick product turnaround. The stakes are high and a quality light hoppy beer is still a rare commodity. Rich spoils await the brewers who can deliver the freshness, and oxygen is the biggest thing standing between fresh beer and their customers.

Brendan Megowan, “A Breath of Fresh Beer”, Beer Paper LA (September 2016), 17.