Ethanol. It’s that wonderful little molecule that makes my wife loopy after too many strawberry daiquiris. It’s the compound that more and more of us are filling our cars up with here in America. It’s really the only thing most of us think of when we hear the word “alcohol”. I say most of us because as beer geeks everywhere know, ethanol isn’t the only alcohol present in beer.

There’s actually a whole host of alcohols floating around in your brews which are collectively referred to as Fusel Oils. These molecules are also sometimes called higher alcohols, because they’re more complicated and much larger in size then plain old ethanol. Some of the more common fusel oils seen in beer include such compounds such as propanol, butanol, and isoamyl alcohol. Beer styles such as barleywines, imperial stouts, and strong bocks are the most common places you’ll encounter these strong molecules.

The most common sensation associated with fusel alcohols is a “hot”, almost spicy flavor that can create a feeling of warmth in your mouth or the back of your throat as your drink. You may also find it presenting itself as a solvent-like flavor in your beer. Fusel oils can often be detected with just a simple sniff of your brew - look for a strong, almost wine-like character to the smell.

Like their cousin ethanol, fusel oils are produced by the metabolic activity of yeast. Unlike ethanol, fusel oils can be further metabolized by yeast during the fermentation process, which eventually results in a variety of different esters being released into your beer. It’s kind of a crazy thing - these super-strong compounds are one of the main reasons you’ll find fruity flavors in some of your favorite brews. If you’re interested in some of the hard-core chemistry behind this process, check out this paper entitled Flavor-Active Esters: Adding Fruitiness to Beer published in the Journal of Bioscience and Bioengineering.

Over time, this ability of yeast to metabolize can have an effect on the fusel oil levels in beers that are bottle-conditioned (beer that’s bottled with still-active yeast). While they certainly won’t eliminate all of the higher alcohols present, aging your bottle-conditioned beers can certainly can help take the edge off a powerfully alcoholic brew. This effect, of course, will only occur as long as the yeast are still alive and kicking in your brew.

So what happens when a beer isn’t bottle conditioned, or the yeast die-off (or autolysis) has already occurred? There is still one reaction that will commonly occur to fusel oils - oxidation. Exactly how much oxidation will occur will vary tremendously with each individual beer, and is generally only something you’ll find out by aging some beers yourself (or checking out my site!). A huge hallmark of oxidized fusel oils is a sherry-like taste and aroma in your brew.

So be sure to let your mind wander to fusel oils next time you’re downing a powerful brew. And be sure to watch for those changes in your cellared beers, I sure will!

Jason

jason@brewbasement.com

www.brewbasement.com