The Magic Of Wine Aromas: A Complex Creation

Wine aromas are created through a combination of the grape, the fermentation process, and oak ageing. The grape variety, soil and climate all contribute to the wine's aroma, with each variety having its own unique aromas and subtleties. In addition, the winemaking process and the type of oak used for ageing can impart compounds that convey vanilla, caramel or coconut aromas. Finally, the ageing process itself can affect the aroma of the wine, with older wines developing more complex tertiary aromas.

How grape-derived aromas are released during fermentation

The process of fermentation turns grape juice into an alcoholic beverage. During this process, yeast transforms sugars present in the juice into ethanol and carbon dioxide. The release of carbon dioxide can strip aromatic substances from the fermenting must.

Grape-derived aromas are released during fermentation through the following processes:

• Yeast metabolism produces higher alcohols and volatile esters, which are responsible for the fruity and floral aromas of wine.
• Yeast releases glycoside hydrolase, which can hydrolyse the flavour precursors of aliphatics, benzene derivatives, monoterpenes, norisoprenoids, and phenols.
• Yeast releases volatile thiols, which contribute to the fruity aromas in wines such as the gooseberry scent commonly associated with Sauvignon blanc.
• Yeast breaks down sugars and amino acids, creating other biochemical compounds that contribute to the flavour and aroma of wine. These include aldehydes, ethyl acetate, esters, fatty acids, fusel oils, hydrogen sulfide, ketones, and mercaptans.
• Yeast can also contribute to wine faults, such as volatile acidity (vinegar taint).

How yeast used for fermentation imparts its own flavours

Yeast is a crucial ingredient in the fermentation process, and it has a significant impact on the aroma and flavour of wine. Yeast is responsible for around 80% of the aromatic compounds that we can smell in wine.

During fermentation, yeast modifies carbohydrates into a variety of metabolic by-products, which give wines their distinctive taste, flavour, and texture. These by-products include esters, which are created by the reaction of acids and alcohol in the wine. Esters can develop during fermentation, with the influence of yeast, or later during aging through chemical reactions. The precise yeast strain used during fermentation and the temperature are two of the strongest indicators of what kind of esters will develop.

Yeasts also produce aromatic compounds that can influence the flavours of the wine. As they ferment, yeasts make alcohol and also produce "fermentation aromas", giving floral and fruity notes such as rose, banana, or peach. Certain "varietal aromas" are also revealed by specific yeasts during fermentation, such as the flavours of grapefruit and passion fruit in Sauvignon Blanc.

In addition, yeasts can act on acidity or produce antioxidants, which can enhance the smoothness of certain white wines and even prevent them from turning brown.

How wine aromas are perceived by the olfactory bulb

The olfactory bulb is a crucial component of our sense of smell, and it plays a significant role in perceiving wine aromas. Here is an in-depth look at how wine aromas are perceived by the olfactory bulb:

The olfactory bulb is a small, onion-shaped structure located at the back of the nasal cavity. It is composed of millions of olfactory receptor cells, each sensitive to a different aroma. When we smell wine, these receptor cells detect the volatile aroma compounds and transmit the information to the brain via electrical micro-currents. This process is known as olfaction, and it is the primary way we perceive wine aromas.

During wine tasting, the act of swirling the wine in the glass increases the rate at which aroma molecules volatilize and reach the olfactory bulb. The shape of the glass also plays a role in capturing and concentrating the aromas. The sense of smell is closely linked to memory, and wine aromas can evoke powerful recollections of specific scents encountered in our lives.

The human olfactory system is unique, and individuals vary in their sensitivity to different aromas. Some people might detect certain aromas that others cannot perceive. Additionally, cultural factors and gender differences may influence aroma perception, with women generally being more sensitive to aromas than men.

The perception of wine aromas is a complex process that involves not only the olfactory bulb but also the interaction of aroma molecules with other components in the wine, such as the nonvolatile wine matrix. The aroma compounds in wine can be categorized into primary, secondary, and tertiary aromas. Primary aromas are derived directly from the grape variety, while secondary aromas develop during the winemaking process and fermentation. Tertiary aromas emerge during the ageing process, especially when the wine is aged in wooden barrels.

The intensity and character of wine aromas can be influenced by factors such as the maturity of the grape, the terroir, and the winemaking process. Additionally, the alcohol content of the wine can affect the perception of certain aroma compounds, with higher alcohol levels tending to mask fruity esters.

In conclusion, the perception of wine aromas by the olfactory bulb is a multifaceted and individualised process that involves the interaction of aroma molecules, the olfactory system, and our sensory memories. The complex array of wine aromas continues to fascinate wine enthusiasts, sommeliers, and scientists alike.

How ageing in wooden barrels creates tertiary aromas

The ageing of wine in wooden barrels is a process that preserves wine and enhances its properties. During the ageing process, wine acquires what is known as its 'bouquet' or 'tertiary aromas'. These are the smells that arise from the chemical reactions of fermentation and ageing.

Barrels are directly involved in the changes that occur in the wine's composition due to the transference of oxygen and phenolic and aromatic compounds from wood to wine. This process is called oxidative ageing and usually takes place in barrels, while reductive ageing occurs in the bottle.

Barrels allow the passage of very low amounts of oxygen, a process called oxygenation. This process gives wine nutty aromas, reminiscent of walnut, toasted almond or hazelnut. The oxygen also helps to stabilise the wine's colour and enrich its sensorial characteristics.

The type of wood used for the barrel also affects the wine's bouquet. American oak barrels impart intense notes of vanilla and coconut, while French oak barrels offer spicier scents such as cinnamon, cloves, molasses or cocoa.

How wine aromas are influenced by vineyard practices

Vineyard practices have a significant influence on the aromas found in wine. For instance, fruit exposed to sunlight will have lower concentrations of methoxypyrazine, the compound responsible for the fresh green and herb characters in Cabernet Sauvignon. In the vineyard, winegrowers can choose to expose the fruit to reduce these characters or shade the berries to achieve a fresher style of wine.

Good levels of nitrogen in the soil can also improve the amount of 3-sulfanylhexan-1-ol (3SH), a molecule that gives grapefruit and passion fruit characteristics to Sauvignon Blanc. Mild water stress can also enhance the presence of 3SH molecules.

Additionally, vineyard management practices such as canopy management can contribute to developing desirable aromatics in the wine. For example, spraying elemental sulfur, an essential tool in organic vineyards, too late in the season can lead to flinty aromas. However, viticulturalists and winemakers usually take extra care to apply fungicides within the recommended withholding periods to avoid this issue.

Furthermore, the region, climate, grape varieties, vinification, and ageing all play a role in shaping the unique expression of wine aromas.

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