What Are Fusel Alcohols (Fusel Oil Explained!)

Any alcohol compound containing more than two atoms of carbon is called a “fusel” alcohol. The word “fusel” comes from German, and means “bad liquor.” Fusel alcohols are sometimes referred to in chemistry texts as “higher alcohols.” Also, because of their oily sheen, they are sometimes also referred to as “fusel oils.”

The following compounds are by-products of fermentation and distillation and are most commonly referred to as fusel alcohols:

  • 1-propanol
  • 2-propanol
  • Butanol
  • Amyl Alcohol
  • Furfural

Table of Contents

Fusel Alcohols Explained

Fusel alcohol forms during fermentation. Fusel alcohol formation is intensified by lower Ph, higher temperature, and insufficient nitrogen for yeast activity.

Fusel alcohols add tastes to liquors and wines. At low concentrations, these compounds give wines some of the distinct aromas and tastes that are so beloved by wine connoisseurs.Some beers, ales, and distilled alcohols also rely on tiny amounts of fusel alcohol to provide distinct flavors. . Other products, such as vodka, are considered best with no fusel alcohol. 

At higher concentrations, they at least make alcohol taste bad. Many fusel alcohols are toxic, and many producers seek to be rid of them in the distillation process.

How Are Fusel Alcohols Produced?

In fermentation, yeast converts sugar to alcohol. Most of the alcohol produced is ethanol. However, the fermentation process can also result in fusel alcohols produced by reaction with amino acids or sugars.

In wine, the main fusel alcohols produced are isoamyl alcohol, active amyl alcohol, isobutyl alcohol, and n-propyl alcohol.

In beers and ales, the fermentation process also yields tyrosol and tryptophol.

The flavor of fusel alcohols vary widely between compounds. Some are pleasant and fruity; indeed, one is used as an artificial banana flavor. Other compounds are harsh, and taste solvent-like, bitter, or hot.

Are Fusel Alcohols Toxic?

There are five main fusel alcohols:

1) 1-propanol is sometimes used as an antiseptic. It is much more toxic than ordinary alcohol, and shouldn’t be consumed. It has a musty smell, and tastes somewhat like fruit, though it also burns the mouth when ingested.

2) 2-propanol is isopropyl alcohol, the common household antiseptic. It is toxic, and not safe to drink. It also has a bitter taste, even in small concentrations.

3) Butanol is one of the least toxic of the fusel alcohols, though still poisonous. However, butanol can cause skin and eye irritation. Some forms of butanol are used in cosmetics and perfumes.

4) Amyl Alcohol is a group of eight related alcohol compounds. All are toxic to some degree. Some of the amyl alcohol compounds have strong smells, and are used in perfumes or cosmetics to yield the scent of roses, carnations, and even bananas.

5) Furfural is a major portion of the fusel alcohols produced in distillation. It has the smell of almonds and darkens in air. It has been shown to be carcinogenic in laboratory animals, though no human studies appear to be available. It is often used as a solvent and industrial chemical.

Fusel Alcohol Toxicity data

The following is LD50 test data for each fusel alcohol.

LD stands for “Lethal Dose” and LD50 is the amount of a substance, given all at once, which causes the death of 50% (half) of a group of test animals [Source].

Fusel Alcohol LD50 / LC50 (Rat) Toxicitiy Results
1-propanol 1870mg/kg (source)
2-propanol 51mg/L 8hr (source)
Butanol 790-4900mg/kg (source)
Amyl Alcohol (Pentan-1-ol) 2200mg/kg (source)
Fufural 127mg/kg (source )

How Are Fusel Alcohols Removed During Distillation?

In distillation, fusel alcohol concentrates at the end of the process in “tails.”

A distiller can reduce the amount of fusel alcohol produced in two ways. First, a longer fermentation period at a lower temperature can reduce the amount of fusel alcohol produced. Second, using ammonium salts, like ammonium phosphate, found in yeast nutrients, can increase the amount of nitrogen available to the yeast, and reduce the fusel alcohols present.

A reflux still is able to remove fusel alcohols almost entirely by separation.

Other methods of removing fusel alcohols include simply skimming them off. Fusel alcohols concentrate near the surface and give alcohol an oily sheen. You can discard the top or first portion of any production run, and eliminate much of the problem.

You can also strain or absorb fusel alcohol from the surface by using a coffee filter or a clean towel, to absorb the top layer of alcohol, where fusel compounds concentrate.

Activated carbon filtering can also remove fusel alcohol compounds.

Frequently Asked Questions:

1. Is Methanol A Fusel Alcohol?

Methanol is sometimes lumped in with fusel alcohols. Methanol is produced in small amounts during fermentation, and not in distillation processes. Methanol is not present in fruit or grain alcohols in concentrations capable of causing harm. It can be reduced (as can the other fusel alcohols) by discarding the “foreshots.” Throwing away the first 50mL of any 20L batch of mash will reduce the amount of methanol in a reflux still. Similarly, discarding the first 150ml per 20L of mash in a pot still will serve for the purpose.

2. What Do Fusel Alcohols Taste Like?

The fusel alcohols all have different tastes. 2-propanol, isopropyl alcohol, has a bitter taste. 1-propanol tastes somewhat like ripe fruit and has a musty smell to it.

1-butanol is permitted, in small amounts, as an artificial flavor additive in the United States, and can sometimes be found in milk products, like butter, ice cream, and cream, in candy, as well as in whisky and rum.

3. Are Fusel Alcohols and Fusel Oils the Same Thing?

The terms are used interchangeably and mean the same thing. American sources tend to refer to “fusel alcohols:” The term “fusel oils” is often used in European sources. The term “higher alcohols” may also be used.

Sources

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7475172/

https://stillontap.ca/how-do-i-get-rid-of-fusel-oils-in-my-spirits/

https://homedistiller.org/wiki/index.php/Amyl_alcohol

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