How to enjoy beer on a sunny day

On these sunny, warm days when a beer patio / beer garden is the most attractive place to sit and have a delicious cool beer, how many of us actually notice the effect of the sunlight on our beers?

Few, for certain.

Despite the resultant pungent flavour — the so-called ‘skunky’ aroma and taste — being extremely potent and obnoxious, the human body’s chemical sensing system can acclimatise to it instantaneously; most people perceive a repulsive odour or taste momentarily, but then fail to detect it a second time without resting the human sensory system.  Some people, however, including most experts and beer aficionados, can detect it continuously.

The skunky flavour is the result of a chemical reaction — technically known as 3-methyl-2-butene-1-thiol (MBT), or more commonly called ‘Lightstruck’ — that commences within a few seconds once a beer is exposed to the visible blue or ultraviolet parts of the light spectrum.  It is most commonly trigged by sunshine and fluorescent lighting, and the odour and taste should be noticeable (albeit momentarily) to regular beer drinkers within a couple of minutes.

MBT is most common in beer sold in clear or green glass bottles, which is why many people who regularly drink Corona or Heineken, for example, become so familiar with the aroma and taste of lightstruck beer that MBT is not recognised as an off-flavour.  Brown bottles, cans, kegs and casks act as filters that minimise the possibility of MBT, but taking your thus far protected beer into the sun counteracts all the brewer’s protective measures.  Bizarrely, there is a common belief that Heineken purposely adds MBT to its canned or kegged beer in order to replicate the lightstruck flavour found in its green bottles, but there is little to substantiate this claim.

Within seconds of reaching a beer, sunshine or fluorescent lighting starts a reaction in the hops’ iso-alpha acids that produces the lightstruck aroma and taste of skunks, which to those unfamiliar with skunks is a flavour reminiscent of gas leaks, burning rubber, sewers, rotten eggs or decomposing vegetables.

There is one way for brewers to avoid lightstruck, skunky flavours, and that is to brew with a specialised hop extract that prevents MBT, although it is rare to find brewers doing so.  The most well-known beers that use this specialised hop extract are those produced by Miller.

If you wish to avoid MBT and its lightstruck, skunky flavours altogether, there are three simple rules to follow:

  • Only purchase beer in clear or green bottles that are guaranteed to have been kept in darkness or preferable conditions from the moment they leave the brewery to the moment you’re served.
  • Don’t drink beer in the daylight (or under fluorescent lighting) that has been served in clear glass, green glass or any other clear vessel.  Or drink it quickly.
  • Drink Miller beers whenever a) you’re unsure whether a clear or green beer bottle has ever been exposed to daylight (or fluorescent lighting), or b) when you really must sit outside and drink beer.

It is a challenge to find a balance between sitting in the sun and enjoying a great, fresh-tasting beer on a sunny day.  If you’re the only people found sitting indoors drinking beer during sunny weather, and outdoor-drinkers consider you unusual for doing so, we hope this short introduction vindicates your decision to avoid mixing beer and sunlight.