Off-flavour #1: Oxidation

The “Off-flavours” series covers the three most common ways the flavour of beer can be ruined after it leaves the brewery and what can be done to prevent this from happening. New to the series? Start here.

Beer is a fascinating, diverse and delicious beverage, but if it’s not properly stored or served, it can develop some not-so-delicious off-flavours. (As a note, none of these off-flavours are health risks, but they certainly are unpleasant!

First up: let’s look at oxidation.

Beer is best consumed fresh, because with time, all beers will develop signs of oxidation, or staling.

What are the signs of oxidation?

Signs of oxidation include:

  1. Hops fade first; both their bitterness and their bright, fresh aromas and flavours decrease.
  2. Next, the “malt shift” follows, introducing overly-sweet caramel or honey-like flavours, along with a waxy flavour that sometimes described as lipstick-like.
  3. Finally, a papery, wet cardboard, or envelope-like aroma and flavour develops; this is a sign that beer is truly past its best.

The rate at which these changes occur will vary, depending on a beer’s ingredients, brewing process or style. Hop-forward styles, like American IPA, experience flavour changes more quickly (in some cases, in as little as 3 months, even if refrigerated) because hops fade first, as noted above.

Alternatively, styles with a full body and high alcohol content can age quite well if properly cellared. (More on this at the end of the article.)

What causes oxidation?

This off-flavour results from beer being exposed to oxygen during the brewing or packaging process. There is always going to be some level of oxygen exposure, but brewers aim to limit it as much as possible.  

When exposed, oxygen binds chemically to certain components in malted barley. The oxygen is then carried through the brewing process in this bound form. Over time these bonds break down, freeing atomic oxygen back into the beer where it can oxidize various compounds in beer – like fatty acids and alcohols – leading to flavour changes. 

How do we prevent the effects of oxidation?

These effects are unavoidable. With time, all beers will develop signs of staling, hence why all beers (should) have a best-by or expiration date. (This is the date by which the brewer believes the beer will no longer represent the brewery-intended flavour due to the effects of oxidation.)

But, we can help to slow their development… by keeping beer cold.

A beer’s shelf life can easily be shortened by exposure to warm temperatures. Refrigerated storage at 3°C (38°F) is best for all beers at all times, as non-refrigerated storage accelerates beer aging. (Cask beer is of course an exception here, as it’s best stored at cellar temperature of 11-13 °C (50-55 °F), but our focus in this series is on other package types.)

It’s important to note that temperature changes within a reasonable range (from refrigerated storage to room temperature storage, for example) will not inherently damage beer’s flavour. But beer should never be allowed to reach temperatures in excess of 25°C (77°F), as these conditions lead to rapid flavour degradation.

(As a note: oxidation can also occur in kegged beers from issues during draught dispense. Read more about it in this article on draught systems here.)

When oxidation is not always an off-flavour

As mentioned above, beer styles with a full body and high alcohol content can age quite well if properly cellared. So what makes them unique?  

Over time, bound oxygen is freed and released back into the beer where it can oxidize the fatty acids and alcohols present. While the oxidation of fatty acids contributes those papery, wet cardboard, or envelope-like aroma and flavours, oxidation of alcohols can actually prove quite pleasant.

As alcohols are oxidized, a port- or sherry-like character becomes evident. Leathery or tobacco-like oxidation character can develop, as well. And the beer will dry out, becoming less sweet and more vinous, or wine-like.

In stronger beers, these positive oxidation flavours can often mask its less pleasant effects.

Additionally, many of these beers are bottle conditioned, which further protects the beer. The live yeast acts as a scavenger for oxygen – using it as a nutrient and preventing oxidation – keeping the beer tasting fresh for longer.

That said though, storage temperature is still important here. Strong beers age best just above cellar temperature, from 55–65°F (13–18°C).

In sum, by keeping beer cold, we can slow the (inevitable) development of oxidative off-flavours.

And now on to our next off-flavour: Lightstruck beer.

Discovering Beer is not affiliated with or endorsed by the Cicerone® Certification Program.

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