In this, the second, installment of our series about off flavors, we take a look at alcohol. While high alcohol is integral to strong craft beer styles such as barleywine and imperial stout, not all alcohols are created equally. Even beers with only moderate alcohol by volume can taste boozy or hot if they’re improperly fermented.
When brewers refer to alcohol without any other qualifications, we’re talking about ethanol (CH3CH2OH), which is the principal alcoholic by-product of yeast fermentation. But it’s not the only alcohol out there. Alcohol is a general name for any organic compound that has a free hydroxyl group (-OH). Other alcohols that can crop up during fermentation include the so-called fusel alcohols:
- Isoamyl alcohol
- Propanol
- Isobutanol
- Butanol
Such secondary alcohols are present in every fermentation to some degree, but in a well-made homebrew, their concentrations are kept well below the threshold of human perception. The problem is that our palates are generally more sensitive to these alcohols than to straight up ethanol, so even small amounts can distract from the overall experience and make a beer taste more like moonshine than homebrew. High-order alcohols are generally described as having a solvent-like flavor, reminiscent of nail polish remover or paint thinner.
Fusels can be appropriate in minute amounts in such high-gravity styles as old ale and barleywine, but a little goes a long way. They are completely inappropriate in most lager styles, with only very low quantities acceptable (but still undesirable) in the strongest doppelbocks.
A surefire way to introduce fusels into your beer is to ferment too warm. Yeast metabolism favors fusels much more at higher temperatures than at low temperatures, so do whatever you must to keep fermentation well within the specified temperature range of your chosen yeast strain. And remember that the temperature measured on the surface of a carboy might be as much as 10°F (6°C) lower than that at the center of the vessel.
Allowing beer to remain in contact with yeast for too long can also create fusels, but we’re talking months, not weeks. So if, like the author, you’re lazy and tend to leave your beer in primary for a month or more before packaging, you need not fear the fusels. However, if you plan to bulk age a barleywine for several months, then racking to secondary is probably worthwhile.