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Troubleshooting A Smoky Off-Flavor


Arthur Davila — Sao Paulo, Brazil asks,

Where do you think a smoked off-flavor (aroma and flavor) may be coming from in a 100% Maris Otter American Pale Ale, with Columbus, Mosaic®, and Citra® hops? The beer was fermented with Voss kveik yeast at 86 °F (30 °C), under 10 psi of pressure, and started clarification yesterday. It clearly did not taste close to what I expected.


I like to troubleshoot off-flavors by thinking through the brewing process as a way of brainstorming. Plugging these thoughts into a visual aid like a fishbone diagram really helps to identify possible causes of the problem in question. Figure 1 illustrates the possible causes of smoky beer aroma that I can think of. I will dig into each of these and hopefully shed some light that may help better understand this problem.

Figure 1

Let’s start with yeast because certain yeast strains are able to convert ferulic acid from malt into 4-vinyl guaiacol (4VG). Although this compound is typically described as clove-like, it can also be perceived as smoky. Low temperature mash rests around 113 °F (45 °C) can increase ferulic acid levels in wort. So-called POF+ yeast strains convert ferulic acid into 4VG. Examples of POF+ (phenolic off-flavor positive) strains include Belgian wit, German weizen, some English ales, all Saccharomyces cerevisae var. diastaticus, and wild yeast. And wort spoilage bacteria, such as Hafnia and, Klebsiella, can also produce 4VG. Yeast is probably the most common cause of phenolic aromas in beer.

Another common source of smoky/phenolic aromas in beer is from chlorine or chloramine in water reacting to phenols produced by yeast during fermentation. Chlorophenols are potently aromatic and are often described as medicinal because some medicinal products, like Chloraseptic®, contain chlorophenols. Campden tablets, aka potassium metabisulfite, can be added to water to remove chlorine and chlorophenols. Activated carbon filtration is another useful method used to dechlorinate brewing water. The idea here is to remove compounds that may react with beer to form smoky aromas.

The last major source of smoky flavors in beer comes directly from malt and/or hops. Malt is smoky when wood smoke or peat reek, i.e., smoke from a peat fire, infuses malt. Smoked malts can contaminate regular malt in mills and grain handling equipment that are not properly cleaned after use and can even taint regular malt when bags of smoked and unsmoked malts are stacked together. Smoke aromas from hops are extremely rare, but wildfires in Oregon and Washington in 2020 and 2021 did damage some hops. Hop processors kept a very keen nose on bales to prevent smoke-tainted hops from being processed, but there have been a few reports from commercial brewers who have run into the odd lot of smoke-tainted hops. The takeaway from this discussion is to smell malt and hops prior to brewing.

OK, so here are my thoughts on your general problem. Voss kveik is not diastatic and is not reported to be POF+. Your hops were most likely not the source given the quality control on them. So that leaves us with water, excessive boiling (this leads to thermal degradation of ferulic acid into 4VG), microbes, and malt contamination as possible causes. Any of these are possible. There is nothing you can do about this brew, but you may want to review your water and how you are boiling before your next brew.

If you have any malt left, consider doing a hot steep and using your nose to determine if there are any smoky aromas that may come from the malt. Maris Otter is definitely not a malt associated with smoke, but several English maltsters produce both Maris Otter malts and peated malts. Contamination can occur during shipping and storage because of the intensity of peat smoke; it’s called reek for a reason! And microbial contamination is always a possibility. Hopefully this gives you some insight into this foggy topic.

Response by Ashton Lewis.