Saturday, 5 June 2010

Flavour Compound of the Week - Octanoic Acid

Does anyone know what a goat smells of?

Having spent most of my life in big towns and cities I have never been near a goat. Certainly not near enough to smell one (honest). I imagine that most of those reading this have also probably never been intimately acquainted with a goat. So describing an aroma as capryilc or goat-like is a bit like saying something smells like the moon. The best way to learn what is meant by goaty is to smell goat’s cheese next to a mild brie. The smell that’s on the goat’s cheese and not on the brie is carprylic. Alternatively befriend a goatherd and get sniffing.
Octanoic acid is described in such a way. Octanoic acid is a short chain fatty acid. Short chain fatty acids are the building blocks of yeast cell walls. The source of octanoic acid in beer is poorly or dead yeast cells. A yeast cell is like a big balloon full of microgiblets (technical term) and a range of chemicals being used to fuel the yeast or build another yeast cell (including octanoic acid). When the yeast is stressed the balloon can become porous and the chemicals and microgiblets leak out. By stressed I don’t mean late for work or in the midst of a bad relationship, I mean placed in a harsh environment. In extreme cases of stress the yeast cell dies and the balloon bursts, this is known as autolysis. Yeast stress, death and autolysis are thought to be the source of octanoic acid in beer. The stress leading to the release of octanoic acid is most oftern caused by high levels of ethanol (alcohol). Alcohol is excreted (pissed out) by yeast as it eats sugar. Unsurprising then, that it doesn’t enjoy swimming around in large amounts of the stuff!

Other short chain fatty acids such as decanoic, dodecanoic and hexanoic acid are also thought to contribute to goat-flavoured beer.

7 comments:

Alan said...
This comment has been removed by the author.
Alan said...

According to wikipedia:
Three such acids are named after goats: caproic (C6), caprylic (C8), capric (C10), totaling 15% in goat milk fat.
so that icludes your decanoic c10 and hexanoic c6.
Intrestingly dodecanoic c12 is also known as lauric acid, a main component of coconut oil which links in to your post about gorse.

Barry M said...

I was going to ask if you mean a Nanny or Billy goat. Having worked down-wind of a billy goat in a previous job, I wouldn't want any of that stink in my beer, or anything else for that matter. They're pretty disgusting in their habits when wanting to appear attractive to the lady goats. Unlike yeast, they're quite happy to lather themselves in piss and other fluids.

I could live with a bit of goats cheese though. Actually, just remembered my wife had a pair of goats before we met. She's often said she'd like another (but not a male!).

Alan said...

You'd have bother getting cheese from the Billy goat though..

Koops said...

Mmmmm. Goat smell. Animal. About the last thing I have thought of is attempting to infuse my homebrew with the smell of wet goat, but now that I think about it...

Stuart Howe said...

Perhaps dodecanoic acid is the smell of goat that's been grazing on gorse flowers.

James said...

Those are the two best ever pictures of goats, and the mention of microgiblets is genius. Can you give an example of a couple of beers with this distinctive taste / nose?

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