Say “Cheese!” Isovaleric Acid in Beer

From beersensoryscience.wordpress.com, writer not attributed. Posts as BeerSensor

Cracking cheese, Gromit!

Have you ever smelled cheese in your beer? How about dirty sweatsocks? It’s more common than you may think. If you’re a homebrewer and you don’t use your hop supply as fast as you should, or if you store them improperly, you may be familiar with this aroma. This is isovaleric acid, and it’s a short-chain fatty acid commonly found in cheese, the valerian herb, foot odor, and sometimes beer. Now that’s an interesting selection of sources!

The commonly accepted threshold for isovaleric acid is about 1ppm, but like most other aromatic compounds, this can vary greatly depending on your genetics. This brief article gives some information about the genetic component of isovaleric acid receptors, exploring some of the sources of variability in how subjects perceive this compound. One of the more interesting things mentioned is that its detection threshold can apparently differ between individuals by up to 10,000 times. Personally, I think my nose has what I call an “acquired anosmia” to this compound. To be anosmic to a particular compound means you can not detect it at any concentration. While my case isn’t that dramatic, I think my sensitivity has dropped due to being frequently exposed to the purified compound when I spike it into my samples (despite using a fume hood and taking protective measures, it’s still possible to get it on you). If you get this stuff on your hands, you’ll stink for the rest of the day, if not longer. For this reason, I often have a hard time being able to tell if my spiked samples are at an appropriate level for the panel. Many times, I have to trust my math more than my nose.

So, how does isovaleric acid get into beer?
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