Red Wine Aromas: Alcohol Content And Its Influence

The aroma of a wine is an important part of the tasting experience. The human nose is capable of differentiating between thousands of unique scents, and it is our olfactory abilities that allow us to discern the variety of flavours in a single sip. The aroma of a wine is influenced by the grape variety used, the winemaking process, and the wine's storage conditions. During the fermentation process, when yeast turns sugar into alcohol, hundreds of flavour compounds are created. These compounds are then inhaled retro-nasally through the back of the mouth to where they are received by nearly five million nerve cells. The act of swirling the wine glass allows the alcohol to volatilise and lift the wine's innate scents towards the nose. The aromas of red wine can include berries, cherries, plums, floral notes, and earthy or woody scents.

Alcohol and acids form esters, which are volatile flavour compounds

The aroma of wine is indeed complex, and it is influenced by many factors, including the grape variety, winemaking process, and storage conditions. While ethanol is the primary alcohol present in wine, other types of alcohols and acids are also present, and they play a crucial role in the formation of esters.

Esters are volatile flavour compounds that are created through the reaction of alcohols and acids. This process occurs during fermentation, with the influence of yeast, and can also develop later during the ageing process through chemical reactions. The specific yeast strain and temperature are critical factors in determining the types of esters that will form.

In wine, esters are responsible for the primary fruit flavours found in young wines. For example, isoamyl acetate and ethyl acetate are commonly found in young, white wines, contributing to flavours of pear drops, bananas, and pears. Other esters, such as octyl acetate, impart aromas of oranges and citrus fruits, while butyl acetate gives off notes of Red Delicious apples.

The formation and composition of esters in wine are dynamic and constantly evolving. During bottle ageing, hydrogen ions, which are more concentrated in low pH (high acid) wines, act as catalysts in the formation of esters from acids and alcohols. At the same time, these hydrogen ions also facilitate the breakdown of esters back into their constituent acids and alcohols. This dynamic equilibrium between formation and breakdown results in a constantly changing ester profile in wine, leading to different aromas at different stages of its life.

Additionally, the distillation procedure can influence the occurrence and concentration of volatile flavour compounds, including esters. In the production of strong spirits, it is common to strip the distillate of low-boiling and high-boiling compounds to enhance the final flavour.

Fermentation creates a wine's secondary aromas

The transformation of grape juice into wine is quite miraculous. With no additives other than yeast, wine develops a stunning array of flavours and aromas, most of which are not present in the pre-fermented liquid. In fact, the aromas of wine are more diverse than its flavours. While the human tongue can only perceive basic tastes like sourness, bitterness, saltiness, sweetness, and savouriness, the wide array of fruit, earthy, leathery, floral, herbal, mineral, and woodsy flavours present in wine are derived from aroma notes sensed by the olfactory bulb.

Wine aromas are classified into three categories: primary, secondary, and tertiary. These aromas appear in the different phases of vinification and can even evolve or disappear over time.

Primary aromas are determined by the vine itself, although other factors like weather, cultivation area, and vineyard soil also influence them. We can identify many of them just by squeezing a grape and, in young wines, they are the easiest to identify. Primary aromas provide floral notes (like jasmine, rose, and honeysuckle) and fruity notes (like blackcurrant, strawberry, and raspberry).

Secondary aromas are derived from the winemaking process, specifically the fermentation phase of the wine (alcoholic and malolactic). This is where notes of yeast, breadcrumbs, butter, cake, bakery, and yogurt appear. The higher or lower intensity of these aromas is determined by the fermentation process, the temperature at which it is carried out, and other factors.

Some other examples of secondary aromas include vanilla spice or toasty notes from new oak barrels, or the buttery, creamy texture that can be a tell-tale sign of malolactic fermentation. This process softens the acidity in a wine by converting malic acid into lactic acid.

Tertiary aromas develop as wine ages. During the ageing phase, wines are modified, and it is with the appearance of these tertiary aromas that we speak of the wine's "bouquet". For example, wines aged in barrels take on aromas of wood, vanilla, toasted, or roasted flavours. In the bottle, they can turn towards ripe and stewed fruit or even leather in red wines, and nuts and honey in white wines.

Aging wine imparts vanilla, baking spices, caramel, and tobacco aromas

The aromas in red wine come from the grape itself, and are the same compounds that occur elsewhere in nature. For example, terpenes, which are found in Riesling, are also found in citrus peels.

Other aromas are created by the fermentation process, while some develop over time as the wine's constituents react with each other. The influence of oak and winemaking practices can also impart compounds that convey vanilla, baking spices, caramel, and tobacco aromas.

Aging wine in oak barrels can impart vanilla and coconut aromas. American oak, in particular, imparts more vanilla and coconut aromas than French oak due to its higher vanillin content. The size of the barrel and the intensity of its toast level influence the amount of spice that a wine absorbs.

Aging wine in oak barrels can also impart baking spice aromas. French oak often brings more savory spice notes, while American oak brings sweeter notes, or baking spices. The spices associated with baking spices include cinnamon, nutmeg, cloves, ginger, cardamom, and allspice.

Aging wine can also impart caramel aromas. Furfural, a chemical found in oak-aged wines, is responsible for the scent of caramel. Furfural forms over time from the decomposition of oak lignin.

Finally, aging wine can impart tobacco aromas. Tobacco aromas are considered tertiary aromas, which emerge as the wine ages in the bottle. These aromas are the result of slow oxidative and reductive processes, which alter the primary and secondary aromatic compounds into a harmonious and intricate bouquet.

Oak-aging results in nutty, buttery, and woody aromas

The aromas of wine are more diverse than its flavours. The human tongue is limited to the primary tastes perceived by taste receptors on the tongue, such as sourness, bitterness, saltiness, sweetness and savouriness. The wide array of fruit, earthy, leathery, floral, herbal, mineral, and woody flavours present in wine are derived from aroma notes sensed by the olfactory bulb.

Oak-aging is a common process that influences the secondary aromas of wine. The most common influence in secondary aromas is oak, imparting nutty, buttery, vanilla and cedar, or other wood-like themes to a final wine. Oak-aging can also result in coconut aromas, as well as woody characteristics like cloves.

The compounds found within oak are responsible for the flavours and aromas that are imparted to wine. Hemicellulose, for example, consists of multiple sugars that are largely unstable and convert once heat is applied, such as when charring a cask. These impart colour to a spirit, as well as caramel, toffee and nutty flavours. Lignin is responsible for vanilla-type flavours, as well as smoky and spicy aromas. Lactone, an organic compound, imparts coconut aromas and a woody character.

The process of oak-aging also influences the chemical compounds found within the wood. Charring and toasting an oak cask creates new, more desirable elements in the wood for the spirit to extract during maturation. It breaks down hemicellulose and converts lignin, for example. The temperature plays a role in this process, as when temperatures rise, the liquid inside an oak barrel expands, which in turn raises the pressure in the cask. As a result, the high pressure forces the spirit into the wood. When temperatures drop, the spirit is then forced out of the wood, extracting flavour compounds along with it.

Wine aromas are derived from the grape, the area, the soil composition, and the climate

Wine aromas are complex and influenced by various factors, including the grape, the area, soil composition, and climate.

The grape variety is a significant contributor to a wine's aroma. Each grape variety has unique volatile compounds that interact with sugars during fermentation to create distinct aromas. For example, the lychee aroma in Gewürztraminer and the black currant note in Cabernet Sauvignon are derived from the grapes themselves.

The area where the grapes are grown, or terroir, also influences wine aromas. Terroir encompasses soil type, underlying geology, and climate. While it is scientifically challenging to taste the soil directly in the wine, soil composition does affect the wine's acidity, pH, and nutrient content, which can subtly influence its aroma. For instance, wines produced from grapes grown in low-pH, nutrient-poor soils tend to have a more rounded taste.

Climate plays a crucial role in shaping wine aromas. Different grape varieties express themselves differently in warm and cool climates. Maritime climates, such as Bordeaux, can produce Cabernet Sauvignons with unique characteristics compared to those from dry and sunny regions like Napa Valley. Climate change is also impacting harvest times and encouraging growers to experiment with different grape varieties that can better withstand higher temperatures.

In addition to these factors, the process of fermentation and aging further develops a wine's aroma. Chemical reactions between acids, sugars, alcohols, and phenolic compounds create new aroma profiles as the wine matures. The interaction of these compounds with the volatile compounds from the grapes results in the complex array of wine aromas that we perceive.

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