What is Fusel Oil?

Fusel oil is a mixture of volatile, oily liquids obtained in small quantities during the fermentation of alcoholic beverages. A typical fusel oil holds 60-70% of amyl alcohol, smaller amounts of isobutyl and n-propyl alcohols, and traces of other components. Prior to the industrial production of synthetic amyl alcohols, which began in the 1920s, fusel oil was the only commercial source of these compounds that are major ingredients of lacquer solvents.


Excessive concentrations of a few alcohols other than ethanol can cause off-flavours, at times, described as "hot", "solvent-like," or "spicy." A few beverages, such as whisky (especially bourbon), rum, incompletely rectified vodka (for example, Siwucha), and ciders and traditional ales, are expected to contain relatively high concentrations of non-hazardous alcohols as a part of their flavour profile. The existence of alcohols other than ethanol in other drinks, such as vodka, Korn, and lagers, may be considered a flaw.

The Chiefly Compounds Involved are:

  • 2-methyl-1-butanol - sometimes known as "active" amyl alcohol

  • isoamyl alcohol (isopentanol)

  • 1-propanol

  • isobutyl alcohol - the least toxic of butanol.

The Following Higher Alcohols Can be Released During Fermentation:

  • Isopropanol (isopropyl alcohol), which is oxidized to form acetone by alcohol dehydrogenase in the liver by leading to ketosis when ingested in larger quantities.

  • 1-butanol

  • 1-pentanol (n-amyl alcohol)

  • 1-hexanol

  • 2-phenyl ethanol


During the process of distillation, fusel alcohols can be concentrated in the "tails" or feints at the end of the distillation run. They contain an oily consistency that is noticeable to the distiller, thus the other name "fusel oil". If desired, these specific heavier alcohols may be almost completely separated in a reflux still. On the other side, freeze distillation does not remove the fusel alcohols.

Fusel Alcohols Can be Formed When Fermentation Occurs:

  • at lower pH

  • at higher temperatures

  • when yeast activity is hampered by a lack of nitrogen

Isobutyl Alcohols

Isobutanol is given as an organic compound having the chemical formula (CH3)2CHCH2OH. This flammable, colourless liquid with a distinct odour is most commonly used as a solvent, either directly or by its esters. The other butanols, its isomers, include 2-butanol, n-butanol, and tert-butanol, all of which are industrially important.

Examples of Isobutyl Alcohols

Some of the Examples of Isobutyl Alcohols are:

  • 2-methyl-1-propanol

  • Isobutyl alcohol

  • 2-methylpropan-1-ol

  • 2-methyl propyl alcohol

  • IBA

  • Isopropyl carbinol

  • 1-hydroxymethyl propane

Secondary Butyl Alcohol vs. Iso- Butyl Alcohol

'Secondary butyl alcohol' is the compound with IUPAC conventional name as butan-2-ol:

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It is a four-carbon chain (butan-) having an alcohol group on the second carbon (-2-ol).

'Isobutyl alcohol' is the compound having the IUPAC conventional name as 2-methylpropan-1-ol:

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The longest carbon chain is 3 atoms (propane-). To this, a methyl group is added to the second carbon (2-methyl-), and an alcohol group is added to the first carbon (-1-ol).

Methylpropane can be used to be called isobutane because it is an isomer of butane, thus the alternative name of isobutyl alcohol. All these names are said to be out of favour and should not be used to avoid confusion.

Working of Alcohol Tolerance

Most people consider being able to hold one's liquor to be a valuable quality. It could save us from embarrassing lapses in judgement and give others the impression that we are safe, robust, and vivacious people, which is particularly important at parties. But that is only half of it.

The road to developing an alcohol tolerance is defined as a slippery slope, which is, to say the least, if we are developing a tolerance, which means we are drinking more and more alcohol. Whereas, in the functional tolerance case, it likely means it is taking place over a sustained period of time because, typically, the liver will retain its "normal processing speed" once the bender is completed.

In the metabolic tolerance cases, which take place in chronic drinkers, the ability to handle increased consumption is more advanced. It importantly means that the metabolic pathways, which are induced by the alcohol in the liver, are jammed open by allowing for a quicker metabolism. In the case of "normal" drinkers, these pathways can be coaxed open only when the alcohol is introduced, which, by that point in time, the person feels intoxicated and stops drinking.

Metabolic tolerance is defined as a dangerous condition because it enables the further destruction of the liver, including other organs, through increased alcohol consumption. Exceptionally, this is lethal for the individual who drinks to get drunk because the damage begins taking place well before the individual feels the requirement to stop.

So, this should be kept in mind that next time we rib someone for not being able to burn the midnight oil. It can just be that their particular bodies are sending the right messages, and are listening, which is cool in a way when we think about it.

Alcohol Tolerance

In general, tolerance develops the more we drink. Tolerance is defined as a psychological and physical need to drink more for a similar feeling of intoxication. But, at the same time, tolerance is the first symptom of alcohol addiction.

Fusel Oil Uses

Fusel oil, including the fusel-oil acetates, can be used in the lacquer industry as the high boiling point solvents.

FAQs (Frequently Asked Questions)

Q1. What happens If We Consume Alcohol?

Answer: If we consume smaller amounts of alcohol and get drunk, then we are more sensitive to alcohol compared to the others surrounding us. Thus, we are at a higher risk of developing an alcohol addiction as well.

Q2. Give the Extraction of Isoamyl Alcohol from Fusel Oil.

Answer: Isoamyl alcohol may be separated from the fusel oil by either of two methods: shaking with a strong brine solution and separation of the oily layer from the brine layer; distilling it, collecting the fraction, which boils between the temperature of 125 and 140 °C.

Further purification can be possible with this procedure: shaking the product with hot lime water and separating the oily layer, and then drying the product with calcium chloride and distilling it, obtaining the boiling fraction between the temperatures of 128 and 132 °C.

Q3. Explain If Isobutyl Alcohol is a Secondary Alcohol.

Answer: Yes, indeed. Since the alpha carbon (the carbon to which the functional group can be added - in this case, the OH group) is attached to the two carbon atoms, isobutyl alcohol is classified as secondary alcohol.

Q4. What are Fusel Alcohols and Esters?

Answer: Both esters and alcohols are extremely important aroma compounds, which help shape the aroma characteristics and flavour of beers. The essential flavour-active esters in beer are isoamyl acetate (fruity, banana aroma), ethyl acetate (fruity, solvent-like), ethyl caproate, isobutyl acetate (pineapple), ethyl caprylate (sour apple), and phenyl ethyl acetate (fruity, flowery, honey, roses).