Chris Shanahan: Keeping the skunk out of beer

Skunky beer? That’s how some describe the smell of a light-struck brew – that garlicky, devil-fart smell hovering over sun-drenched beer gardens. It’s not pleasant.

It seems that when light strikes beer, it triggers a reaction in hop-derived iso-alpha acids and amino acids to form mercaptans – a particularly smelly family of sulphur compounds found in everything from decaying vegetable matter to skunk secretions.

Clearly, mercaptan has no place in beer. The trouble is, though, that for aesthetic reasons, much of the beer sold today comes in clear or green glass bottles. And these offer far less light protection than brown glass or the perfectly dark inside of a keg.

If they could, brewers might use nothing but kegs and brown glass. But that’s not on. So many now employ modified hop extracts – proprietary products like ‘tetrahop gold’ — that provide light resistance and, in so doing, keep the skunk out of our beer.