I’ll never forget the first time I encountered solvent character in my homebrew. It was one of my first attempts at high-gravity beer (a Belgian dark strong ale, specifically), and I had been told that an elevated temperature was key to achieving the necessary attenuation. I (under) pitched Wyeast 1762 Belgian Abbey II into 1.085 wort at 72°F (22°C) and let it go: I’m pretty sure fermentation topped out well north of 80°F (27°C).
I succeeded in achieving excellent attenuation, but I paid a dear price for it. The resulting beer had a hot, burning character that in very small amounts might have actually been pleasant. Instead, I had made five gallons of paint thinner.
Solvent character is almost always the result of fermenting too hot. Generally speaking, the hotter the fermentation, the hotter the beer. High temperatures crank yeast metabolism into high gear, but in doing so, our fungal friends create more of what are known as acetate esters. Such esters are members of the same family as many of your favorite industrial chemicals, including paint thinner, nail polish remover, varnish, spot remover, turpentine, epoxy, and super glue.
The key to avoiding these unwanted flavors is temperature control. Fermenting at the low end of a strain’s preferred temperature range will suppress much of the yeast’s production of these compounds, but frequently with lower attenuation. A good way to get the best of both worlds is to pitch at the low end of the range and allow the fermentation temperature to gradually warm to the higher end of the range over the course of a few days.
It’s also true that some yeast strains are more prone to creating these flavors than others, but implementing temperature control frees you to ferment any strain you wish within its optimal range. If this isn’t possible for your set-up, then consider switching to a strain that can tolerate more heat.
Oxidation can also result in solvent-like flaws. As always, move your beer quietly, and remember that oxygen should touch only freshly prepared wort that’s ready for pitching, but it should never touch your beer.
Finally, not all solvent character comes from yeast: Your equipment may play a role as well. Make sure to use plastics that are food grade and rated to the temperatures used in brewing. Look at obvious sources such as fermentation buckets and mash tuns, but also consider smaller pieces such as gaskets and tubing. Better to spend a little more on brewery-approved plastics than dump a batch down the drain.