Aroma and flavour: composition of coffee

Aroma is one of the first senses experienced when preparing or consuming a coffee beverage.  However, being largely composed of ‘volatile compounds’ that easily evaporate at room temperature, aroma is also one of the most variable components of the sensory experience2.

Approximately 850 volatile compounds have been identified that are associated with flavour in coffee.  However, a small proportion of these (approximately 40 volatile compounds) with low odour thresholds and/or high concentrations are known to be the main contributors to coffee aroma3,4. The main volatile compounds in coffee include carbonyl, sulfur alicyclic aromatic benzenoid and heterocyclic compounds5. Further information on the composition of coffee can be found here.

Coffee aroma arises from different volatile compounds produced during the roasting of coffee.  Coffee oil, which makes up approximately 10% of roast coffee beans, carries the most flavour6.

As such, green coffee beans, or beans before roasting, have a limited aroma profile that is often described as providing green or musty notes.  However, green beans contain a large number of precursors including sugars, other carbohydrates and nitrogen compounds, which develop into aromatic compounds during the roasting process7.

Roasting triggers a series of chemical processes within the beans causing the development of volatile compounds that contribute to the aroma profile.  These processes include the Maillard Reaction, or non-enzymic browning (resulting from heat applied to nitrogen and carbohydrate containing compounds), Strecker degradation (resulting from the interaction between amino acids and a carbonyl compound in water), and degradation of individual amino acids, trigonelline, sugar, phenoic acids and lipids5.

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