Friday, 9 April 2010

Flavour Compound of the Week - Trans-2-nonenal

Trans-2-nonenal (3-Hexyl-2-propenal) gives beer a cardboard flavour. It reminds me of old chip wrappers. Try an out of date bottle of commodity lager if you want to taste it on beer. It is produced by the oxidation of a precursor derived from malt. Trans-2-nonenal is a member of a large group of compounds called unsaturated aldehydes which give beer an old and stale flavour. If you limit the concentration of oxygen in the beer you reduce the rate of oxidation of these unsaturated aldehydes. Brewers who filter yeast out of beer work very hard to keep oxygen to a minimum so that it doesn't damage the flavour.

Anheuser busch used to have the industry's lowest specification for oxygen concentration in beer. Any form of flavour in a cool crisp beechwood sawdust-matured Bud would stick out like a sore thumb! I'm not sure if InBev have continued this tradition. I'm sure les comptables are looking into it. In cask and bottle conditioned beer yeast will absorb oxygen to keep the beer fresher for longer. All beer goes stale and old in the end (yeast seldom survives in the bottle/cask for more than a year or so).

Some drinkers enjoy very old beers which are full of what are described in brewing text books as stale flavours. Some say that they taste like drinking the contents of an pub ashtray out of a prop forward's rugby boot. I find them interesting but aside from lambics which are already just about as oxidised as they can be, I’ve never found a beer to improve after 4-5 years.

Each to their own.


ZakAvery said...

I'm with you about beer not getting better after a few years, with a tiny number of exceptions. But at the risk of being a pain in the arse, I'm sure the text on St Enodoc Dubbel claims that the beer will improve indefinitely.

Stuart Howe said...

Very sharp Mr Avery! I could say that statement was made knowing that temptation would be too great to leave the bottle longer than a few weeks. What I will say is that I don't write the labels Zak even though they do bear my signature. I'll get it changed on the next print run.

I suppose you could argue as that indefinite is by its very nature indefinite! Who's to say when a period of indefinity ends. If a period of indefinity falls over when no one is around, does it make a sound? Have I just sampled 23 batches of beer in an hour?

I have some first run St Enodoc from 2004 and it's still good albeit not as good as it was at its peak.

Korev said...

I think the Cornish term "directly" could be used to advantage here?

ZakAvery said...

As I say, just being a pain in the arse!

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