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.