Types of Aromatic Molecules

Key Aroma Families and How They Shape Flavour

Aromatic molecules are volatile compounds that activate the olfactory system and define much of what we perceive as flavour. Understanding their main families helps explain how raw materials, fermentation, distillation and ageing create specific aromatic profiles.

Terpenes

Terpenes occur naturally in citrus peels, conifers, herbs, and many botanical ingredients. They are responsible for the pine character of juniper, the brightness of citrus, and part of the aromatic profile of hops. Their diversity explains why botanicals offer so many different aromatic facets. In spirits, terpenes are central to gin, while in beer they define many hop-driven styles.

Aldehydes

Aldehydes are primarily formed through the oxidation of primary alcohols, which can happen during production or ageing. They contribute aromas ranging from green, grassy notes (such as hexanal) to almond-like profiles (such as benzaldehyde). In whisky, brandy and aged wines, aldehydes increase through controlled contact with oxygen, adding complexity as the liquid matures.

Ketones

Ketones form mostly during fermentation and, in some cases, during ageing. They can contribute sweet, fruity or buttery notes depending on their concentration. Diacetyl is the best-known example: it can create buttery characteristics in beer or wine if fermentation conditions allow it to accumulate. Their presence is linked to yeast metabolism and how fermentation is managed.

Esters

Esters form when alcohols react with acids, especially during fermentation. They provide many of the fruity and floral aromas in drinks. Their formation is strongly influenced by yeast strain, temperature and fermentation time. Esters play a major role in the aromatic identity of rum, Belgian beers, and many fruit-driven spirits.

Lactones

Lactones develop largely during barrel ageing. They arise from interactions between the spirit, oxygen, and wood components. Depending on the oak species and toasting level, lactones can contribute coconut-like, creamy or stone-fruit notes. They are especially prominent in spirits aged in American oak, such as bourbon and certain rums.

Phenols

Phenols can develop through thermal or microbial processes. In spirits, they are most associated with peat smoke, where drying malt over burning peat introduces phenolic compounds that contribute smoky or medicinal notes in whisky. In beer and wine, some yeasts can also produce phenolic aromas that appear as clove-like or spicy characteristics.

Higher Alcohols (Fusel Oils)

Higher alcohols are produced naturally during fermentation as by-products of yeast metabolism. In excessive amounts they can appear harsh or solvent-like, but in lower concentrations they add weight and complexity. Their levels depend on fermentation temperature, yeast health and nutrient availability, making them an important aspect of producing clean, balanced spirits.