Solvent flavors are a very common occurrence in aged beers. In higher amounts, solvent flavor is associated with a harsh chemical-like taste in your beer, and definitely not a good thing at all. In smaller amounts however, it can add some pleasing complexity to your brew by lending a tart, almost green-apple like background flavor. The taste has even been identified as “warming” before. The primary molecule responsible for this solvent flavor is called Furfuryl Ethyl Ether, or FEE for short.

In fresh beer, FEE is only present in very minor amounts. This is because its formation is not a direct result of the brewing process. Rather, FEE is formed in a complex reaction that occurs between the alcohol in beer (ethanol), the water, and various precursor molecules. The precursor molecules for FEE are present in the beer either as a result of the initial brewing or gradually formed as other molecules in the beer degrade over time.

There are many factors that can contribute to the rate at which FEE will build up in your beer, but the most important one by far is temperature. In an aging beer there is a direct correlation between FEE build up and rising temperatures. Beer held at a point near freezing will show very little FEE formation, while FEE in beer that is being held at a temperature over 100 F has been shown to develop detectable solvent flavors within days. Other important considerations when looking at the FEE reaction rate is that beers that are high in ABV% and/or dark in color are much more prone to FEE development, as are beers that are low in pH.

So what does this all mean for your cellar collection? First thing to realize is that there will almost always be some FEE formation in your brew, which may even be a positive thing for it’s flavor profile. Second thing to remember is that the higher temperature your beer is stored at, the faster FEE will build up in your brew. Don’t ever store your precious beers in a hot garage, not even for a day or two! Thirdly, take note of the solvent flavors in your beer whenever you open one up. If you’re starting to notice the flavors associated with FEE are appearing stronger and/or faster in your brew, you’ll might want to consider either drinking them soon or stashing them in the fridge in order to slow down the FEE reaction rates.

That’s all for now, thanks for reading!

Jason

jason@brewbasement.com

Information in this article was taken from two articles that have appeared in the Journal of Agricultural and Food Chemistry called “Evolution of Chemical and Sensory Properties during Aging of Top-Fermented Beer” and “Furfuryl Ethyl Ether: Important Aging Flavor and a New Marker for the Storage Conditions of Beer” by Bart Vanderhaegen and colleagues.