They have 6 to 3 carbon atoms per molecule. The name fusel oil is derived from 'fuseln' (German language) which means 'to bungle'. These are obtained via the yeast-based metabolisation of nitrogenous compounds. It refers to the leftovers of the batch or pot distillation that are usually have low volatility characteristics. 

Fusel oil suppliers generally collect them as parts of the distillate. They are then processed and imparted their own individual flavours. Since they are relatively harsher in nature, these require more time to mature and integrate. They predominantly include higher alcohols such as esters, amyl alcohol aldehydes, hexanol, butyl and fatty acids.

Its most common application is that it is used to add boozy notes to other alcoholic drinks. It can give flavor to whiskey, wine, tequila, rum, brandy and cider. It is also used selectively in the food industry to overripe notes.