The organisation of wine aroma and its evolution over time

The aroma of wine: a question of chemistry and perception

The aroma of wine represents one of the most fascinating and complex sensory aspects of wine tasting. Wine communicates through its smell, telling the story of the terroir, the grape varieties and the oenological techniques used in winemaking. Understanding the formation and evolution of aromas is essential for oenologists and winemakers, as the aromatic bouquet affects not only the perceived quality of the wine, but also its longevity and commercial value.
In this article we will explore the mechanisms that regulate the organisation of wine aroma and its evolution over time, analysing the volatile compounds involved, the role of the chemical matrix and the transformations that occur during ageing.

The complexity of olfactory analysis

Wine aroma analysis is an extremely complex process, as it involves the interaction of several senses: smell, taste and feel. In addition, the influence of sight and the taster’s cognitive expectations can alter aromatic perception, making objective analysis difficult.
Wine aromas are determined by volatile molecules that reach the olfactory epithelium via two main pathways:

• Direct (orthonasal) route: when we smell the wine in the glass.
• Retronasal route: when aromas are perceived during swallowing, through the connection between the oral cavity and the nasal cavity.

The molecules responsible for the aroma of wine

The main classes of volatile compounds

More than 1,000 volatile molecules have been identified in wine, but the overall bouquet can be explained by about 100 major compounds. Among the most important categories are:

• Terpenes (e.g. linalool, geraniol): they contribute floral notes, typical of Muscat and Gewürztraminer.
• Volatile thiols (e.g. 3MH, 4MMP): responsible for fruity and tropical aromas, typical of Sauvignon Blanc.
• Norisoprenoids (e.g. β-damascenone, TDN): contribute to fruity and spicy aromas and develop with ageing.
• Aldehydes and volatile alcohols: result from oxidation and can contribute herbal or oxidative notes.
• Pyrazines: determine vegetal and herbaceous aromas, characteristic of Cabernet Sauvignon and Sauvignon Blanc.

Olfactory perception and perception thresholds

Not all volatile molecules present in wine are sensorially active: they must exceed their olfactory perception threshold to be perceived. Some molecules are active at very low concentrations (e.g. thiols at a few nanograms per litre), while others must be present in high quantities to be detectable.
In addition, synergism between molecules plays a crucial role: the combination of two compounds can generate a new and unexpected aroma, distinct from that of the individual substances (olfactory imaging phenomenon).

Aroma precursors and aroma release over time

Combined precursors and free precursors

Wine aromas can manifest themselves in two ways

• Free: immediately perceptible in young wine.
• Combined: sensorially inactive, but releasable over time by chemical or enzymatic processes.

A classic example is the bound terpenes of Gewürztraminer, which are progressively released during ageing, contributing to the longevity of the wine.

The role of time and ageing conditions

The development of the aromatic bouquet depends on several factors:

• Wine pH: an acidic environment favours the hydrolysis of aromatic precursors.
• Storage temperature: heat accelerates chemical reactions, with the risk of degrading certain aromas.
• Presence of oxygen: can favour the oxidation of certain compounds, altering the aromatic profile.

This is the case of Riesling, whose longevity is determined by the progressive release of TDN (responsible for the paraffinic notes of aged wines).

Oenological strategies to optimise the wine’s aromatic profile

Winemaking techniques to enhance aromas

To preserve and enhance the aromas of wine, winemakers adopt several strategies, among them

• Yeast selection: Some strains release thiols and terpenes during fermentation.
• Cold maceration: useful for extracting aromatic precursors from the skins.
• Temperature-controlled fermentation: to avoid the loss of volatile molecules.
• Ageing on fine lees: favours the hydrolysis of aromatic precursors, prolonging aromatic persistence.

The balance between evolution and oxidation

An aged wine can develop a more complex bouquet, but risks losing freshness due to oxidation. The key to optimal evolution is the right balance between:

• Primary aromas (floral and fruity) → they tend to diminish over time.
• Secondary aromas (fermentative) → derive from yeasts and evolve gradually.
• Tertiary (ageing) aromas → develop with ageing and include notes of honey, spices and hydrocarbons.

In Gewürztraminer, for example, the high content of bound precursors ensures a slow and continuous release of terpenes, maintaining the aromatic complexity of the wine even after years.

Conclusion

The organisation of wine aroma and its evolution over time are the result of a complex interaction between chemistry, sensory perception and oenological techniques. Understanding the mechanisms that regulate the release and transformation of aromas is essential to optimise the quality of wine and ensure its long life.
The winemaker, through specific choices in winemaking and ageing, can significantly influence the aromatic profile, ensuring that the wine not only expresses its full potential in its youth, but also maintains a harmonious and balanced olfactory structure over time.

This informative article, written by the editorial staff of Infowine, has been extracted from the lecture ‘The organization of wine aroma and its evolution during time’ given by Luigi Moio, University of Naples.