What Are Congeners? Definition and Examples

What Are Congeners
Congeners refer to closely-related things, including similar compounds in alcohol, organisms within the same genus in biology, or related structures in chemistry.

Congeners are defined as substances or organisms with similar functions, structures, or origins. The term has specific meanings in different disciplines. Here are the definitions and examples of congeners in chemistry, alcoholic beverages, and biology.

Definition of Congeners

Depending on the discipline, congener means different things:


In biology, congeners are two organisms that belong to the same genus. They share a common ancestor and are very similar to one another. For example, dogs (Canis familiaris), coyotes (Canis latrans), and gray wolves (Canis lupus) are different species that are all members of the same genus (Canis) and are congeners. Members of Canis can interbreed, but this is not the case for all congeners. For example, horses (Equus ferus) and donkeys (Equus africanus) are congeners and can interbreed, but their offspring typically are sterile. Congeners also exist in other kingdoms of life, including plants, bacteria, and even viruses.


In chemistry, congeners refer to substances with similar structures, functions, or origins:

  • Compounds with similar structures are congeners, such as sodium chloride (NaCl) and sodium fluoride (NaF) or hydrogen peroxide (HOOH) and hydrogen disulfide (HSSH).
  • The term also applies to elements in the same group on the periodic table, such as lithium and sodium or chlorine and bromine.
  • Compounds containing different oxidation states of the same element are congeners. For example, titanium(II) chloride and titanium(IV) chloride are congeners.

Alcoholic Beverages

A specific application of the chemistry definition of congener applies to alcoholic beverages. Here, congeners are desirable or undesirable products of fermentation that are not ethanol (the kind of alcohol you drink). Some of these compounds are toxic, while others add color, flavor and aroma.

Here are examples of congeners in alcohol:

  • Acetone
  • Acids
  • Alcohols (e.g., methanol, isobutylene alcohol and other fusel alcohols)
  • Aldehydes (e.g., acetaldehyde, which gives bourbon a fruity odor)
  • Esters
  • Ketones
  • Tannins

Colorless, purified alcohol is low in congeners. However, even colorless alcohol contains congeners if it is insufficiently purified. Dark or colored types of alcohol typically contain more congeners. Here, the congeners often add a desirable character, yet they may also contribute to hangovers. In addition to purity, the source material for fermentation also affects the type of congeners.

Examples of alcohol low in congeners include vodka, white wine, sake, gin, and beer. Whiskey, cognac, brandy, rum, red wine, and tequila tend to be high in congeners. Even clear tequila typically contains low levels of methanol.


  • Hawksworth, D. L. (2010). Terms Used in Bionomenclature: The Naming of Organisms and Plant Communities : Including Terms Used in Botanical, Cultivated Plant, Phylogenetic, Phytosociological, Prokaryote (bacteriological), Virus, and Zoological Nomenclature. GBIF. ISBN 978-87-92020-09-3.
  • IUPAC (1997). “Congener”. Compendium of Chemical Terminology (the “Gold Book”) (2nd ed.). Blackwell Scientific Publications. doi:10.1351/goldbook.CT06819
  • Rohsenow D. J.; Howland J.; Arnedt J. T.; Almeida A. B.; Greece J.; Minsky S.; Kempler C. S.; Sales S. (2010). “Intoxication with bourbon versus vodka: effects on hangover, sleep, and next-day neurocognitive performance in young adults”. Alcoholism: Clinical and Experimental Research. 34 (3): 509–18. doi:10.1111/j.1530-0277.2009.01116.x
  • Rohsenow, D.J.; Howland, J. (2010). “The role of beverage congeners in hangover and other residual effects of alcohol intoxication: a review”. Current Drug Abuse Reviews. 3 (2): 76–9. doi:10.2174/1874473711003020076

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