Higher Alcohol Off-Odors in Wine

Did you ever create a wine that seemed more viscous than your typical wine, or which may have exhibited heavier fruity odors, or perhaps a solvent-like smell? The culprits may well be higher alcohols, also called fusel oils; all wines contain some at various concentrations. Higher alcohols in small concentrations can contribute positive aromatic characteristics to wine; however, at high levels they can impart off-aromas or mask other aromas, or change the texture and mouthfeel. So, what are higher alcohols exactly? Where do they come from? What’s with the Jekyll-and-Hyde behavior? And most important for us winemakers, how can we control their production? The chemistry of higher alcohols As is the case with all alcohols, including ethanol (which is the primary alcohol in wine, beer and distilled spirits), higher alcohols have a special functional group called a hydroxyl (OH) group that defines their chemical be-havior. The main difference lies in the number of carbon atoms in their molecular structure. Ethanol has the chemical formula C2H6O (also written as C2H5OH) and so it has two carbon atoms. Higher alcohols are defined