The universe in a glass and the chemistry of varietal aromas: a journey into three white wines

“A poet once said: The whole universe is in a glass of wine. We will probably never know in what sense he meant that, for poets do not write to be understood. But it is true that if we look at a glass of wine closely enough, we see the entire universe. There are the things of physics: The twisting liquid which evaporates depending on the wind and weather, the reflections in the glass, and our imagination adds the atoms. The glass is a distillation of the earth’s rocks, and in its composition we see the secrets of the universe’s age and the evolution of stars. What strange arrays of chemicals are in wine? How did they come to be? There are the ferments, the enzymes the substrates and the products. There in wine is found the great generalisation: all life is fermentation. Nobody can discover the chemistry of wine without discovering the cause of much disease. How vivid is the Claret, pressing its existence onto the consciousness that watches it! If our small minds, for some convenience, divide this glass of wine, this universe into parts: physics, biology, geology, astronomy, psychology, and so on, remember that nature does not know it! So let us put it all back together, not forgetting ultimately what it’s for. Let it give us one more final pleasure, drink it and forget it all!”

-Richard P. Feynman, physicist and Noble prize winner

I have always been drawn to art, also for reasons beyond the appreciation of aesthetic beauty. At times emotive, at times evocative, at its best it is an opportunity to look at things differently. It can reflect your inner sentiments, it can change your perspective, and it can encourage you to not take things on face value alone, but to look deeper.

For these same reasons, I believe that wine is a work of art. A product of nature, wielded and transformed by man, it exists beyond its face value within the contexts of history, geography, science and much more. Learning about wine teaches you such things as the history, language and culture of another country, the topography of wine regions and where they’re located in the world, the life cycles of plants, and the chemical reactions that occur in wine making. It soon becomes impossible to look at wine as just an alcoholic beverage. It reveals itself to the curious and attentive drinker as a multifaceted world layered with complexity and beauty.

I have had the perspective altering experience of seeing wine as a combination of chemicals interacting to create a universe of sensations in a glass thanks to Luigi Moio’s book Il Respiro del Vino (The Breath of Wine). Having gone on a journey through the chemistry behind aromas in wine, it is something that I can certainly no longer take for granted and my perception, and consequently my enjoyment of wine, has been wonderfully enriched.

Let me illustrate my point with an exploration of varietal aromas in three white wines…

Some wines are easily recognisable in a blind tasting because they contain specific chemical compounds which release specific aromas, allowing the wine to be identified. These are known as varietal aromas and may be present in the grapes themselves or form during or after fermentation. An aromatic varietal is a grape variety that contains specific aroma compounds in the grapes themselves which are also present in the wine after fermentation, which also classes them as primary aromas. Some aromatic grape varieties include Moscato, Malvasia and Gewürztraminer. Other varietal aromas either come from precursory aroma compounds that are released during fermentation or compounds formed during this process, making them also secondary aromas. Some varietal aromas only become present in the wine after ageing through the degradation and combination of aroma compounds, making them also tertiary aromas.

Below are three examples of three different white wines with three different varietal aromas from three different stages of wine making.

Floral aromas in Moscato

The typical floral aromas in Moscato are due to a large quantity of monoterpenes, above all linalool, also found in many flowers like roses and lavender. Linalolo is present in the grapes of Moscato, uniformly distributed between the skin and pulp. While many other red and white grapes contain this compound as well, the elevated concentration in this grape variety gives the wine its distinctive floral character. Because a large percentage of the compound is in a liberated form, a floral aroma is present both in the grapes and the wine, making it a primary aroma and classing Moscato as an aromatic wine.

Leafy aromas in Sauvignon Blanc

The typical leafy aromas of Sauvignon Blanc are due to the formation of volatile thiols during fermentation. The grapes and the must are almost odourless, making this varietal aroma a secondary aroma. The volatile thiols that form are not generally high in concentration, but have a low threshold of perception making them easily perceived by the human nose. Typical aromas derived from these compounds vary from exotic fruit to apple, lemon zest, Mediterranean flowers and box wood (the bushy plant used generally in gardens). In fact, the intense, leafy aroma of boxwood is also sometimes perceived as cat pee!

Petrol aromas in Riesling

A typical aroma of aged Riesling is petrol. This aroma is due to high concentrations of the chemical TDN which derives from the degradation of carotenoids, usually about 2-3 years after alcoholic fermentation. Carotenoids are organic pigments which can be found in grape skins and serve as percursory aromas, meaning the aroma is not present in the grapes, the must or the wine after fermentation, but forms and increases in intensity with ageing in the bottle. Other factors that accelerate the formation of TDN are hot climates, excessive maturation of grapes and bottles exposed to high temperatures. So while other white wines may contain TDN, a dominating aroma of petrol would be considered a defect. In an AGED Riesling it is a delightful tertiary aroma typical of the varietal.

That being said, in the words of Richard Feynman,

“Let us put it all back together, not forgetting ultimately what it’s for. Let it gives one more final pleasure, drink it and forget about it all!”

Source: Il Respiro del Vino, Luigi Moio