Wine Aroma: Foods To Avoid For The Perfect Scent

The aroma of wine is determined by a large number of chemical compounds. These compounds can be divided into primary, secondary and tertiary aroma. Primary aroma originates from grape berries and it is distinctive for each variety, but it also depends on environmental factors, climate, berries conditions, etc. The amount of aroma compounds that will be transferred into the grape must and wine depends on vinification techniques, especially maceration and extraction. Secondary aroma compounds are formed during alcoholic (converting sugar to ethanol) and lactic (converting malic to lactic acid) fermentation. Tertiary aroma (bouquet) is formed during wine storage and aging. The final aroma depends on chemical composition of wine, pH, containers for wine aging (wood, stainless steel), maturation strategies, temperature, aeration, etc.

Volatile compounds

To date, over 1,000 volatile compounds have been found in wines, with a total content of approximately 0.8–1.2 g/L. The volatile compounds in the groups of alcohols, esters, aldehydes, ketones, acids, terpenes, phenols, and sulfur compounds are the primary components at varying concentrations, from nanograms per liter to milligrams per liter.

Moderate concentrations of some of the volatiles considered to have high odor intensity, such as 3-methyl-1-butanol, 2-phenylethanol, or isoamyl alcohol, can have a positive impact on the wine by providing floral, honey, and fruity aroma notes. Optimal alcohol values under 300 mg/L provide fruity and floral notes, whereas alcohol values above 400 mg/L become negative by adding pungent and unpleasant aromas.

Esters generally have positive effects on the aroma of young wines, especially those with neutral flavors. However, excessive amounts of esters may induce negative effects on wine quality. A high concentration of esters can hide varietal aromas and simplify the composition of the aroma of the final product or spoil wine. For example, if ethyl acetate exceeds 150–200 mg/L, it can negatively impact the wine.

The use of mixed or sequential fermentations can help regulate the content of medium-chain fatty acids, as their excessive presence may provide negative aromas with greasy, rancid, and cheesy notes.

Fermentation

The fermentation process is key to developing the aroma of wine. During fermentation, the wine's aromatic complexity increases dramatically, with the highest levels of volatile compounds produced during the yeast growth phase.

The type of yeast used is a key parameter in the final concentration of alcohol in wine, and thus its aroma. Different yeasts have been used to give complexity to wines through ester production, including S. cerevisiae, Candida, Hansenula, and Pichia. These non-saccharomyces yeasts can positively influence the aroma profile and enhance or decrease the production of some aroma compounds. For example, the use of mixed or sequential fermentations of C. stellata and S. cerevisiae can increase the amount of hexanoic and octanoic acids, while also reducing the concentration of fatty acids, which may otherwise provide negative aromas with greasy, rancid, and cheesy notes.

The amount of volatile sulphur compounds produced during fermentation can also negatively affect wine quality. Sulphur compounds are formed as byproducts of yeast metabolism, and their amount can be reduced by adding suitable nutrition and a suitable strain of yeast. The use of non-saccharomyces yeasts in coinoculation with saccharomyces yeasts can effectively reduce the amount of acetic acid, which can negatively impact the wine's aroma when it exceeds a specific threshold.

Other factors that influence the final concentration of alcohol and the aroma of wine include temperature, pH, oxygen, grape ripeness, and variety. For instance, optimal alcohol values under 300 mg/L provide fruity and flowery notes, whereas alcohol values above 400 mg/L add pungent and unpleasant aromas.

Ageing

The ageing of wine is a complex process that significantly influences the wine's aroma profile. As a wine matures, its bouquet evolves and becomes more multi-layered, transitioning from prominent fruity notes in younger wines to a more intricate interplay of fruit, floral, earthy, mineral, and oak-derived aromas.

During ageing, wine can undergo a "dumb phase", akin to a teenager's difficult age, where its aromas and flavours become muted. This phase varies in duration and is not yet fully understood. However, as the wine emerges from this muted stage, its aroma evolves, and the lingering finish lengthens.

The type of oak used in ageing and the degree of toasting applied to the barrel play pivotal roles in shaping the wine's aroma. Oak ageing can impart sweet aromas of vanilla, caramel, brown sugar, and butterscotch. The subtle introduction of oxygen through the wooden barrel can contribute to nutty nuances in the wine's bouquet. Opting for a heavily toasted oak barrel can introduce more robust aromas, such as smoke, tobacco, cigar, and dried leaves.

Additionally, the ageing process can soften the harsh tannins characteristic of young red wines, resulting in a smoother mouthfeel. This maturation also manifests visually, as the once inky dark colour of the wine gradually lightens, first showing orange hues at the edges before eventually turning brown.

The bottle storage period also influences the wine's aroma. With extended storage, factors such as the cork, temperature, and light can increase the wine's oxidation rate, leading to a range of aroma transformations. For instance, oxidation can enhance cooked vegetable and caramel odours while diminishing fruity, floral, and tropical fruit aromas.

Wine matrix

The aroma of wine is a complex and delicate matter, with many factors influencing the final scent. The type of yeast used in fermentation, for instance, can have a significant impact on the wine's aroma profile. While S. cerevisiae is commonly employed in wine production, non-saccharomyces yeasts like Candida, Hansenula, and Pichia can introduce novel aromas, enhancing the complexity of the wine. These non-saccharomyces yeasts can positively or negatively influence the production of certain aroma compounds, resulting in unique sensory attributes.

Additionally, the concentration of certain compounds, such as acetic acid, plays a crucial role in the wine's aroma. Low levels of acetic acid can lend a pleasant, nutty, or sherry-like aroma to the wine, while higher concentrations can lead to an unpleasant smell. The sensory threshold for acceptable levels of acetic acid varies depending on the wine type, with dry wines being more sensitive to its presence than sweet wines.

Another critical factor is the management of alcohol levels in the wine. Optimal alcohol values below 300 mg/L contribute desirable fruity and floral notes, whereas alcohol concentrations surpassing 400 mg/L can introduce pungent and unpleasant aromas. The fermentation parameters, including yeast strain, temperature, pH, oxygen levels, grape ripeness, and variety, all play a role in determining the final alcohol concentration.

Furthermore, esters, which are commonly introduced through specific yeast strains, can have a positive impact on young wines, especially those with neutral flavours. However, similar to higher alcohols, excessive amounts of esters can negatively affect the wine's quality. A high ester concentration can overpower varietal aromas and simplify the overall aroma composition.

The presence of medium-chain fatty acids, such as hexanoic and octanoic acids, should also be carefully monitored. Their excessive presence can introduce negative aromas, imparting greasy, rancid, or cheesy notes to the wine. Winemakers can employ mixed or sequential fermentations to regulate the content of these fatty acids and maintain a balanced aroma profile.

Physiological parameters

The aroma of wine is influenced by a variety of physiological parameters, including the type of yeast and bacteria used during fermentation, the concentration of certain chemical compounds, and the sensory threshold of the drinker.

Yeast plays a crucial role in wine aroma. Different strains of yeast can affect the final concentration of alcohol and the production of ester, which contributes to the aroma of young wines. For example, S. cerevisiae is commonly used for its desirable characteristics, while non-saccharomyces yeasts like Candida, Hansenula, and Pichia can introduce novel aromas due to their differential enzymatic mechanisms. Additionally, mixed or sequential fermentations using S. cerevisiae and non-saccharomyces yeasts can help regulate the content of medium-chain fatty acids, as excessive amounts may lead to negative, rancid, or cheesy notes in the wine.

The concentration of specific chemical compounds can also impact wine aroma. Higher alcohol concentrations can affect the complexity of the aroma composition. Optimal alcohol values under 300 mg/L provide pleasant fruity and flowery notes, while concentrations above 400 mg/L can result in pungent and unpleasant aromas. Similarly, moderate concentrations of certain volatile compounds, such as 3-methyl-1-butanol, 2-phenylethanol, or isoamyl alcohol, contribute positive floral, honey, and fruit aroma notes. However, excessive amounts of esters may have negative effects, masking varietal aromas and simplifying the overall aroma profile.

Acetic acid concentration is another important parameter. Lower concentrations provide a vinegar-like sourness and nutty aroma, often associated with sweet wines. However, as the concentration increases, it can become unpleasant. The sensory threshold at which acetic acid becomes undesirable depends on the type of wine. For example, in Canadian sweet wines, the threshold is between 1.0 and 1.5 g/L, while in dry wines, it must not exceed 1.0 g/L.

Additionally, ethyl acetate, a compound related to AAB metabolism, can positively contribute to a floral or fruity aroma in wine. However, when it exceeds a certain threshold, it becomes undesirable, similar to the effect of high acetic acid concentrations.

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