Solventy off-flavors in beer can be described as having pungent, acrid aromas followed by a harsh, burning, or warming sensation on the back of the tongue that persists in extreme cases. Reminiscent of acetone or nail polish remover, it can also be described as paint thinner (e.g., toluene, turpentine), mineral spirits, polyurethane varnishes, lacquer, sanitary cleaners (citrus terpenes), dry cleaning chemicals (e.g., tetrachloroethylene), glue solvents (acetone, methyl acetate, ethyl acetate), spot removers (e.g., hexane, petrol ether), polyester resins, vinyl and adhesives, two-part epoxies, and superglue.
The source of solvent off-flavors in beer can most commonly be traced to two sources, those arising from tainted or contaminated equipment (inferior can liner curing, plasticizer leaching from tank linings, or gaskets), and flavor-active substances produced by yeast cells during fermentation—namely, higher alcohols and their acetate esters.
Some 45 higher alcohols have been identified in beer. Those of importance for aroma, because they occur at concentrations near or above their flavor thresholds are n-propanol, isobutanol, 2-methylbutanol (amyl alcohol), and 3-methylbutanol (isoamyl alcohol). Referred to as aliphatic alcohols, they contribute to beer flavor by general intensification of alcoholic/solvent-like aroma and taste with a corresponding warming effect on the palate. Aromatic alcohols of concern are tryptophol and tyrosol (when present in too high a concentration) are described as chemical or solvent and can cause lingering harshness and after bitter and are generally regarded as negative to beer flavor.
Control of higher alcohol formation during fermentation can be accomplished in three ways: by choice of an appropriate yeast strain, by modification of the wort, and by manipulation of fermentation conditions.
Volatile esters, although present in only trace amounts in beer, comprise the most important set of aroma-active compounds.