Time Heals Many Wounds: What to do about Common Off-Flavors By: Kay Witkiewicz
If you’ve ever tippled a sample of your homebrew before it was a finished beer and thought something along the lines of, “Yuck! This doesn’t taste anything like what I want it to!” then don’t despair for too long. Depending on the beer you’ve brewed, there’s an optimal window during which to consume it and many off-flavors you’ve noticed along the way are likely to mellow out over time. There are three common off-flavors that you can directly diminish in your beers with proper conditioning practices and plenty of patience: diacetyl, husky and grainy flavors, and fusel alcohols.
Diacetyl is a yeast-derived flavor compound that is generally detected as butter or butterscotch in taste and aroma when present above its threshold level of 0.04 mg/L. During the vigorous growth phase of fermentation, yeast produces a precursor to diacetyl, which it then reabsorbs during the stationary phase of fermentation when yeast growth slows significantly. Each yeast strain produces differing levels of diacetyl, with some British strains expressing higher concentrations that are characteristic of some ales and stouts of that region. For example, I brewed a stout with WLP004 Irish Ale Yeast, and its sweet, buttery hint of diacetyl actually complements the roasted and dark chocolate flavors of the beer quite well. Nonetheless, when I brew this beer again, there are several strategies I will use to reduce its noticeable diacetyl character. Even if your beer has finished fermenting and reached its expected final gravity, increasing the beer’s contact time with the yeast will allow the latter to absorb more of the diacetyl precursor it expressed during the growth phase. I racked my stout after 13 days in primary, but having tasted it now, I will likely keep it there a handful of days longer when I brew it again. Keeping your fermentation temperatures constant is also a way to limit diacetyl. Many of us likely pitch our yeast at a warmer temperature than we plan to ferment our beer at in order to reduce lag time and drive yeast growth. However, by pitching warm and then cooling during fermentation, the yeast will have a tougher time reducing the diacetyl created at the start, thus leaving your beer with more diacetyl character than may be desired. One way to overcome residual diacetyl due to temperature discrepancies is to institute a diacetyl rest between 68 and 72 degrees Fahrenheit. Allowing your primary fermenter to warm up to that temperature range, especially if it’s a lager, will spur the yeast into further absorbing diacetyl. Certain bacteria will also produce diacetyl. Taking the time to properly clean and sanitize your racking and bottling equipment and, especially, your bottles is the only way to prevent diacetyl production this late in your beer’s maturation process. Being patient with your beer when it’s in the primary fermenter, maintaining constant temperatures from the time you pitch your yeast until you bottle, and keeping your equipment clean and sanitary are all successful strategies to limiting the diacetyl character in your beers.
Husky and Grainy Flavors
Have you ever brewed a really malty beer, but when you sampled it you felt as if you had plunged face-first into a grain silo? Particularly husky and grainy flavors in your unfinished homebrews can either be the sign of a young beer that simply needs more time to mature or it can represent a production problem, namely over-sparging your grains. I have experienced such flavors with two of my beers: an American brown ale and a British brown ale. The American brown ale utilized a combination of about 25% Munich 10L and Caramel 80L along with a small addition of rye malt. Tasting it after 10 and 19 days, respectively, the prominent grain flavors, likely due to the high percentage of caramel malts and the rye, had already mellowed out and by the time I cracked open the first bottle a month after I brewed the beer, it was a beautiful symphony of American hops in the nose and complex yet refined malt flavors in the mouth. For similar reasons, I expected the British brown ale to also exhibit husky characteristics since I brewed it strictly using the second runnings of a Scotch ale mash with the addition of some crystal and chocolate malts. The second runnings of a mash are generally grainier in taste and aroma than the first runnings since most of the sugars have already been dissolved and drained into the brew kettle. Still, by using unique yeast—WLP013 London Ale Yeast has assertive woodsy characteristics—and allowing the beer to condition in the bottle in a stable environment, this beer turned out to be a subtle surprise in flavor and aroma. If you’re brewing an extract-based beer with specialty grains, one way to reduce husky flavors is to rinse your grains responsibly. Rinse your grains with about as much water (below 170 degrees Fahrenheit) as you used to steep or mini-mash them in the first place, gently massage your grain bag, and you will extract most of the sugars without the tannins from your grains. If you’re brewing all-grain, sparge with only as much water as you need to bring your brew kettle volume up to your intended level and you will likely avoid excessive graininess. In any case, stable storage conditions and time will meld your grainy flavors into the magnificent malty notes you expected in the first place.
If you’ve ever opened your primary or secondary fermenter and almost been knocked out by a strong whiff of alcohol more reminiscent of liquor than beer, then you have experienced the powerful characteristics of fusel alcohols. Fusel alcohols are byproducts of fermentation and in lower concentrations provide the warming sensations characteristic of high-gravity beers, but in excessive concentrations they can add hot, solvent-like, and other distracting flavors. High-gravity wort naturally stresses the yeast, thus producing higher levels of fusel alcohols in the finished beer, but two ways to keep this byproduct from becoming an off-flavor are temperature control and time. Ale yeasts produce higher concentrations of fusel alcohols than lager yeasts, likely due to their higher fermentation temperatures. Hence, keeping your fermentation temperatures toward the low end of your yeast strain’s recommended range will help you depress fusel alcohol levels. The first few days of fermentation are crucial in this regard because during the growth phase, the temperature in your primary fermenter will skyrocket. One of the reasons why my aforementioned stout also exhibits some fusel alcohol characteristics is because late on the first day of fermentation, my temperature shot up to 74 degrees Fahrenheit, six degrees past the upper limit of its optimal range. Your beer can contain any combination of about 40 different fusel alcohols, and time is the only way to mute some that stand out in your beer’s flavor profile. Between bottling day and today (about 30 days) the fusel alcohol character in my stout has mellowed out and blended with the diacetyl, roasted, and chocolate notes of the beer to produce a flawed but enjoyable end product. Fusel alcohols are part and parcel of fermentation, but constant temperature control of your primary and secondary fermenters as well as a little patience will yield a tasty concoction.
Whether on brewing day, during fermentation, or while bottling, we have all sampled our homebrewed creations before we ever served them to ourselves and our friends as finished beers. Tasting your homebrews at varying stages of the production process allows you to chart the development of their flavor profiles and adjust your conditioning practices, namely by simply being more patient. Timing is crucial in producing good beer. Leaving your beer in contact with the yeast an extra couple of days beyond the completion of fermentation will reduce diacetyl levels, while storing your primary and secondary fermenters, as well as your bottles, in stable, temperature-controlled environments for a few weeks will diminish husky and grainy flavors and fusel alcohol characteristics. Off-flavors are part of homebrewing, but it’s how you manage them that will ultimately determine the quality and the popular impression of your finished beer.