If you’ve ever used the words clovey, spicy, or smokey when describing the flavor or aroma of a beer, you’ve probably tasted a phenol. Unfortunately, band-aid-like, plastic, bleach-like and medicinal also happen to fall into the phenolic flavor profile and are the more common perceptions being described when someone says a beer is “phenolic.”
Phenols are a class of chemical compounds consisting of a hydroxyl group (-OH) bonded to an aromatic hydrocarbon group.
There are hundreds of different types of phenols, many of which can show up in your beer. Chemistry aside, the one common thread that binds all of these different chemical compound is that they have extremely low detection thresholds; meaning you can taste and smell them even if they are present in very small amounts.
The ability for most people to easily detect phenols, coupled with the fact that most phenolic attributes are considered a flaw in your beer means that a brewer, or just a brew drinker, should have an understanding of why they are there.
Typically and fortunately, undesirable phenolic compounds in beer that produce very unpleasant hints of medicine, plastic or bleach come from poor brewing practice and can easily be eliminated.
Old, unhealthy and wild strains of yeast are common producers of off flavored phenols. Bacterial contamination in your brew can also be a factor in phenol production. Make sure your yeast is fresh, don’t over wash it and ensure you are using proper cleaning/sterilization techniques.
Phenols are naturally extracted from malted grains during a brewers mash and sparge operation in large chains called poly-phenols. Some of these compounds are referred to by brewers as tannins. An over abundance of poly-phenols can give your beer an astringent or bitter flavor. It can also cause chill haze, which is a permanent clouding of a beers appearance. Any brewer trying to prevent too many poly-phenols should avoid over-crushed grains, never over-sparge, keep the sparge temperature below 170°F and ensure your sparge water is below pH 6.
High levels of chlorine in your water or leftover chlorine from equipment cleaning can lead to the production of chlorophenols. Chlorophenols are produced when chlorine reacts with the naturally produced phenols in your brew, giving off a very strong bleach-like aroma and flavor. If you believe this to be a problem in your brew, investigate your cleaning techniques and your water quality. Consider charcoal filtering or using bottled water if your believe chlorophenols are hurting your beer.
With all of that said, let’s move on to the lighter side of phenols. Some phenol flavors and aromas are desirable and necessary to properly produce certain styles of beer. These desirable phenols are produced by specialized strains of yeast. Many wheat beers will display a spicy, clove like aroma due to the yeasts metabolism of ferulic acid. Ferulic acid is much more abundant in malted wheat than malted barley. Typically, German and Belgian beers rely heavily on this phenol production for their flavor. One of the most common and popular beers that you’ll find phenolic flavors in is a hefeweizen, or it’s unclouded cousin, the kristallweizen. Both beers are known mainly for their clovey notes but may also contain faint smokey flavors. Australian Bitters also are produced with phenolic flavors in mind but at much lower levels than their Bavarian and Belgian counterparts.
Phenols, while generally a sign of poor beer production when detected are not necessarily always a brewers enemy. Next time you taste a beer with a hint of spice, clove or smoke you can recognize it for what it is; a tiny little phenol that your yeasty friends added to your brew because they love you.