This informative article, edited by Infowine, is taken from the lecture ‘The organisation of wine aroma and its evolution over time’ given by Luigi Moio, University of Naples (see the first part here). The text contains links to further information on the various topics covered.
The aroma of wine is the result of a complex interaction between chemical compounds derived from grapes, fermentation and ageing. Understanding the layering of aromas and their evolution over time is essential for winemakers. This article explores the main factors that determine the aroma of wine and how they develop during the winemaking process.
The formation of primary aromas: the smell of grapes and must
The primary aromas of wine come directly from the grapes and are closely linked to the variety used. However, not all grapes have immediately perceptible aromatic compounds. A prime example is Trebbiano, a variety that lacks significant aromatic precursors, unlike Moscatello, which is rich in terpenes, responsible for its floral notes.
In neutral musts, the predominant aroma is herbaceous, due to the enzymatic degradation of linoleic and linolenic acids. This reaction leads to the formation of six-carbon alcohols and aldehydes (hexanal, cis-3-hexenal, trans-2-hexenal), which are responsible for the typical vegetal notes.
Furthermore, in some varieties such as Sauvignon Blanc or Cabernet Sauvignon, the must contains compounds such as pyrazines, which intensify the herbaceous character.
The role of fermentation: acids, higher alcohols and esters
During alcoholic fermentation, yeasts convert sugars into ethyl alcohol and carbon dioxide. In addition to these main products, acids (acetic, butanoic, hexanoic, octanoic) are also generated, some of which, in high concentrations, can impart unpleasant notes, such as those of cheese or stables.
Higher alcohols, such as 3-methylbutanol, 2-methylbutanol and 2-phenylethanol, develop simultaneously and contribute variable sensory characteristics. 2-Phenylethanol, in particular, adds subtle floral notes of rose, while other higher alcohols, such as amyl and isoamyl alcohol, can be reminiscent of solvents or varnishes.
Esters are formed by the reaction between alcohols and acids during fermentation and are responsible for the fruity and fresh notes of young wines. Among the most significant esters are:
- Isoamyl acetate (banana)
- Ethyl butanoate (pineapple)
- Ethyl octanoate (tropical fruit)
The balance between esters and higher alcohols determines the aromatic profile of the wine. If esters predominate, the wine acquires a fruity and pleasant character, while if higher alcohols dominate, the olfactory profile tends to be more generic and vinous.
The evolution of aroma over time: olfactory stratification
The aroma of wine can be described as a layering of volatile components that combine and transform over time. Five main layers can be identified:
1 – Aldehydes and six-carbon alcohols: responsible for the initial herbaceous notes.
2 – Ethyl alcohol and fatty acids: these form the olfactory base common to all wines.
3 – Higher alcohols: they add complexity, but can be perceived as defects if present in excess.
4 – Esters: they give young wines freshness and fruity notes.
5 – Varietal-specific compounds: these are terpenes (Muscat), thiols (Sauvignon Blanc), methoxypyrazines (Cabernet Sauvignon) and rotundone (Syrah), which give the wine its varietal identity.
The role of the fermentative aromatic base
One of the most interesting aspects is the so-called ‘ fermentative aromatic base’, a set of molecules common to all wines, including alcohols, organic acids, esters and acetaldehyde. This base acts as an ‘aromatic buffer’, absorbing most sensory changes and allowing only certain compounds to emerge.
Molecules such as isoamyl acetate and beta-damascenone are among the few capable of modifying this base, adding distinctive characteristics to the wine’s olfactory profile.
The aroma of wine as an olfactory orchestra
The analysis of the complex aromatic structure of wine can be compared to an olfactory orchestra.
Some varietal wines stand out for the presence of a dominant molecule, a true ‘soloist’ that guides the aromatic perception. This is the case, for example, with Sauvignon Blanc, where volatile thiols play a fundamental role in defining the bouquet.
On the other hand, there are “orchestral” wines, without a single dominant molecule, in which the olfactory perception results from the balance between several aromatic components.
In these cases, environmental and terroir variability has a greater influence, making the wine’s identity more sensitive to external factors.
The evolution of wine aroma over time
Wine ageing is a dynamic process in which the chemical balance between volatile molecules undergoes continuous transformation. Fruity esters, which are initially predominant in young wines, tend to hydrolyse over time, releasing alcohols and acids that can negatively affect the aromatic perception.
This transition phase can lead to a temporary decrease in olfactory intensity, a sort of “dormant phase” in which the wine appears aromatically neutral. Subsequently, if the wine has sufficient aromatic precursors, these can release new odorous molecules, restoring complexity and richness to the bouquet.
The role of oxygen in aromatic evolution
One of the key elements in the transformation of wine aromas is oxygen. Its impact varies depending on the type of wine:
- In white wines, oxygen poses a significant threat, promoting the formation of compounds such as acetaldehyde and phenylacetaldehyde, which are responsible for unpleasant oxidative notes, such as baked apple or caramel.
- In red wines, on the other hand, the presence of anthocyanins and tannins provides natural antioxidant protection, slowing down the degradation processes.
Controlling oxygen during vinification and storage is therefore essential to preserve the aromatic quality of wine over time.
Temperature and stability of esters
Another determining factor in the evolution of wine aroma is storage temperature. Scientific studies have shown that high temperatures accelerate the degradation of volatile esters, reducing the aromatic freshness of wine.
For example, isoamyl acetate, responsible for banana notes in young wines, hydrolyses rapidly at temperatures above 20°C. In contrast, more resistant ethyl esters can contribute to greater aromatic longevity, making them particularly desirable for the production of wines intended for ageing.
The interaction between wood and wine aroma
Ageing in wood introduces an additional element of complexity to the evolution of a wine’s aroma. Oak barrels produce phenolic compounds such as vanillin and whisky lactone, which interact with the existing aromatic profile.
In wines with low aromatic potential, these compounds can dominate the varietal characteristics, leading to an excessive presence of woody notes. Conversely, in wines with high aromatic potential, the presence of precursors allows for a harmonious fusion between the varietal aromas and the compounds released by the barrel, ensuring greater balance and complexity.
Conclusion
The aroma of wine is the result of a complex balance between volatile molecules that evolve during vinification and ageing. Understanding these processes allows professionals to intervene in fermentation and cellar techniques to obtain the desired aromatic profiles.
This informative article, written by the editorial staff of Infowine, is taken from the lecture ‘The organisation of wine aroma and its evolution over time’ given by Luigi Moio, University of Naples (see the first part here).
