Phenols represent a broad class of compounds that may be very welcome or completely undesirable in beer, depending on the brewer’s intention and the target style. Chemically speaking, a phenolic compound contains hydroxyl (OH) and a ring of hydrogen and carbon molecules (an aromatic hydrocarbon ring). Such compounds are prolific in nature and are responsible for many well-known flavors and aromas:
- Capsaicin gives chiles their fiery bite.
- Carvacrol is responsible for oregano’s pungency.
- Eugenol is found in cloves, nutmeg, cinnamon, and vanilla.
- Guaiacol is the smoky essence in whiskey and roasted coffee.
- Methyl salicylate smells and tastes just like wintergreen.
- Raspberry ketone smells like raspberries.
- Thymol is what gives thyme its distinctive aroma.
Phenolic compounds are also produced synthetically for industrial and pharmaceutical applications. But when it comes to beer, you may or may not want phenolic character. As usual, it really depends on what you’re after:
- Bavarian Weißbier, or Hefeweizen derives its signature clove character from 4-vinyl guaiacol.
- Saison often contains a mix of clove and pepper-like phenols.
- Brettanomyces-driven styles are often described as horsey or barnyard-like thanks to 4-ethyl phenol.
While cloves, pepper, and even sweaty horse blankets may be desirable in certain brews, other phenolic flavors are rarely welcome guests. If your beer tastes of plastic, smoke, Chloraseptic, or Band-Aids, then look to these potential sources.
Chlorine in Your Brewing Water
This is enemy number one. Chlorine reacts with yeast-derived phenols to create chlorophenols, which come across the palate as plastic-like or reminiscent of adhesive bandages. Switch to bottled water or simply allow your tap water to sit overnight: The chlorine will naturally diffuse into the air, and you’ll be ready to brew the next day.
If you use a chlorine-based sanitizer such as bleach, then it’s important to completely rinse your brewing equipment after sanitizing. Or just switch to a no-rinse sanitizer such as Star-San or Iodophor and be done with it.
Consider your yeast selection. Belgian strains and Bavarian Weißbier yeasts offer up clove-like phenols, and the many varieties of Brettanomyces can introduce their own horsey and smoky attributes. Look to American, British, and continental lager strains for relief.
Make sure your sanitation is top notch. Wild yeasts and unwanted bacteria may be to blame for smoky and plastic-like flavors, especially if the effect gets worse with time or if the phenolic character is accompanied by acetic or lactic sourness. Look at hard-to-clean pieces of equipment and consider replacing plastic pieces if the issue comes up repeatedly.
If you find that your beer turns out exceptionally bitter or astringent, tannins may be your problem, in which case it’s time to re-visit your sparging routine. Make sure to keep the grain bed below 168°F (76°C) at all times, and stop sparging when the runoff gravity drops below 1.010.
As with many of the other off-flavors, you may or may not want phenolic character in the beer you’re making. What’s appropriate in a Bavarian Hefeweizen is completely out of place in a Bavarian Helles. Know what you want ahead of time, and if you detect unwanted phenols, consider the above sources to keep your next batch phenol-free.