How do I get rid of Fusel Oils in my Spirits?

By Hendre’ Barnard, Training and Marketing Manager
Distillique Beverage (Pty) Ltd.

How do I get rid of Fusel Oils in my Spirits?

That is one of the questions everyone always asks me. First you need to know where Fusel oils comes from. Fusel alcohols or fuselol, also sometimes called fusel oils, are mixtures of several alcohols (chiefly amyl alcohol) produced as a by-product during alcoholic fermentation.

The word Fusel is from the German word that means “bad liquor”.

What different Types of Fusel Alcohols are there?

Fusel Alcohols can be classified into two different categories

1. Hazardous Alcohols

  • Methanol (methyl alcohol), a poisonous compound (Lethal Dosage of 5 628 mg/kg if consumed orally)
  • Isopropanol (isopropyl alcohol), which is oxidized to form acetone by alcohol dehydrogenase in the liver

2. Congeners

Excessive concentrations of some alcohols other than ethanol may cause off-flavours, sometimes described as “spicy”, “hot”, or “solvent-like”.

Some beverages, such as rum, whisky (especially Bourbon), incompletely rectified vodka (for instance Siwucha), and traditional ales and ciders, are expected to have relatively high concentrations of non-hazardous alcohols as part of their flavor profile.

However, in other beverages, such as Cane, Vodka, and Beers (Lagers specifically), the presence of alcohols other than ethanol is considered a fault.

The compounds involved are chiefly:

  • 2-Methyl-1-Butanol – sometimes called “active” Amyl Alcohol
  • Isoamyl Alcohol (Isopentanol)
  • Isobutyl Alcohol – one of the least toxic of the Butanols
  • N-Propyl Alcohol

Where do Fusel Alcohols come from?

Fusel alcohols are always formed during fermentation, but the amount or concentration of Fusel Oils is increased dramatically if and when Fermentation occurs:

  • at higher temperatures (normally above 22 degrees Celsius)
  • at lower pH (too acidic)
  • when yeast activity is limited by low nitrogen content (insufficient nutrients)

During distillation, most fusel alcohols are concentrated in the feints or “tails” at the end of the distillation run.

They have an oily consistency, which is noticeable to the distiller, hence the other name “fusel oil”.

If desired, these heavier alcohols can be almost completely separated in an Adjustable Reflux Still or Fractionating Reflux Column Still.

Do Fusel Oils cause Hangovers?

A lot of people are of the opinion that Fusel Oils cause or contribute to hangovers.

This is a matter of scientific debate.

A Japanese study in 2003 concluded: “the fusel oil in whisky had no effect on the ethanol-induced emetic response”.

It must be said however, that the Japanese used the common Asian House Shrew as a test subject, so you would not be blamed if you thought you smelled a Rat. (Sorry, I had too).

What are the Facts about Fusel Oils?

Fusel oil is the common or encompassing name for by-products as well as higher alcohols formed in the fermentation process – it is therefore not a pure compound or compounds but considered to be a mixture.

The principal ingredient of fusel oil is amylalcohol which comprises 65-80% of fusel oil.

It may also contain all forms of isobutylcarbinol and damylalcohol, and may contain between 15-25% of isobutyl- and approximately 4-7% of n-propyl alcohol.

Amyl-, butyl- and propylalcohols therefore form the bulk of fusel oils.

Other substances are present, although none in significant quantities – the amounts are in fact so small that one needs only consider the principal components when doing an analysis.

The figures above covers quite a range (65 to 80%, 15 to 25% and 4 to 7%).

The actual makeup of fusel oil depends principally on the ingredients of the fermentation, the fermentation temperature, and to a lesser extent the Fermentation variables like pH and Nutrients.

Why would Fusel Oils be desired in Spirit?

Fusel oil is the aroma of the mash.

For example, in brandy and other fruit-base spirits (for example Slivovitz, Calvados, Rakia, Palinka, Palene, Piore Williams, etc.) the Fusel Oil content in the final product is normally 0.6% or more.

This is the principal aroma of the spirit, and after storage and maturing, most of the Fusel Oil constituents are converted to esters.

However, even in basic raw spirit distilled from a sugar wash, the Fusel content can be between 0.4 – 0.7% of the 95% alcohol.

The type of fermentation alone is therefore no indication or guarantee that you will or will not produce large quantities of Fusel Oils.

Can I reduce Fusel Oil Formation during Fermentation?

The addition of ammonium salts to a Fermentation reduces the formation of fusel oil.

This is referred to as Yeast Nutrient Salt (normally Ammonium Phosphate), a common ingredient or component of Yeast Nutrients.

In addition, fermenting at a lower temperature for a longer period of time should also form less Fusel Oils.

Can I remove Fusel Oils from my Distillate?

When spirits is diluted down to 40 – 50% ABV, some of the fusel oil will go out of solution, and take on an oily consistency.

This is amplified if the solution is kept cool, either in the fridge (if it is a sample bottle or something produced by a Home Distiller) or through the use of a Cooling Jacket, Cooling Coils or Refrigeration Panels in a Holding Tank on the Commercial Level.

The Fusel Oils that separate out are the insoluble fusel oils, principally Amylalcohols.

The separated fusel oil floats up to the surface due to its lower specific weight, where it can be removed by various methods.

At the Home level this could be as simple as dabbing with an absorbent paper or tissue, or even filtering through coffee filters – commercially you would use a paper plate filter – Chilled Filtration.

As long as the temperature is below 15°C and effective filtering is used, you should be able to can separate approximately 0.3% of the fusel oil (15 ml of 5 liters of spirits) calculated on 95% ABV spirits.

This should be more than one third of the fusel oil present.

If needed, the results can then be further purified using Activated Carbon Filtration.