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

Richard Feynman giving a lecture to university students
Richard Feynman giving a lecture to university students

“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

The intersections of wine and chemistry

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.

A universe in a glass

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.

Luigi Moio’s book “Il Respiro del Vino” (The Breath of Wine)
Luigi Moio’s book “Il Respiro del Vino” (The Breath of Wine)

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.

The law of conservation of mass discovers by Antoine Lavoisier, the father of modern chemistry, in 1774
The law of conservation of mass discovered by Antoine Lavoisier, father of modern chemistry, in 1774

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

13 Comments

  1. A very clear post, probably your best, and three good examples of wines and chemicals causing or related to specific aromas of fruit, leaf etc. The world of chemistry has come a long way in relation to understanding the nature of petrol and cats pee in wines, but there is still a great deal of unexplained phenomena in relation to variations in perception from one person to another, or one day to the next for the same person. I’m starting to liken it to the classic optical illusion drawings, one minute an old woman, next minute a young woman, you see young, I see old! Yet we are both looking at the same drawing, we both have the same brain structures, our optical systems are identical. So why, why, why the difference?

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    1. I like the optical illusion example! I guess it harps back to perception being influenced by innumerable factors like upbringing, culture, clearness of mind and focus, mood, etc. Some research has been done on the effect of the moon on our perception. Sometimes I watch a film I’ve seen before again and feel something completely different. I think quantum physics talks about the randomness of events in the universe. But at least statistically speaking, there are generalised agreements about aromas in wine which make up some kind of comprehensible whole.

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      1. As a trained scientist with a PhD in chemistry, I learned a very long time ago about the dangers of generalisations. I have faith, belief, and acceptance of observed evidence of every chemical identified in a wine. But my scepticism arises from psychological and neuroscience generalisations about aromas and flavours, and then wine professionals writing about them as if they are a fixed and universal phenomenon that SHOULD be observed by everyone . Consider this, did your sommelier training educate your palate, your synapses or your mind?

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      2. Oh, it’s getting messy! I’m with you on wine professionals asserting aromas as fixed and universal… I think very few things are, if any. Generalisations are dangerous, but they’re also part of human nature, how can we possibly process and communicate everything that bombards are senses? Even if we both accept that there is an identifiable chemical with a floral aroma in the wine, our understanding of it would be very different, mine in some ways a leap of faith due to limited understanding and lack of a contextual knowledge of chemistry. As for the training, I think all three and none of them at the same time. They gave me the knowledge, the opportunity to engage empirically with wine tasting, and the context of other trainees and sommeliers but my understanding and appropriation of terms relative to that context was a personal cognitive journey. They always stressed that wine tasting is subjective, but certain parameters of evaluation serve to avoid judgements based on preferences or prejudices alone and to create a language in which we can all comprehend each other… which is maybe a sort of generalisation in a sense, but I’d have to think about that more.

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  2. Thank you for this beautiful post. I love it how you move from art to chemistry in such an elegant way. And I still insist that you should read Armando Castagnos work.😊🍷

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    1. I’m so glad you enjoyed it! In my attempt to understand the beautiful complexity of chemistry I’ve had to resort to seeing it through an artistic lens 😅 Armando Castagno is the one who talks about wine through art history, right? What do you recommend I read?

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  3. How is your Italian? Not sure he has anything translated into English. I am right now reading “Vini artigianali italiani” by Castagno/Gravina/Rizzari, a book in which a wine (artisanal/natural and small scall mostly) is connected to an art work. Really reccomend it!

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    1. Sounds perfect! I should be able to manage in Italian. I’ll definitely look for it. By the way, I’m reading your thesis. It’s a very interesting breakdown of images within a cultural context, great job!

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      1. Thank you so much!! It was interesting writing it and I learned a lot about Slow Food while working on it. I wrote another thesis last year during my Master here in Italy, if you would be interested in having a look, but it has a more historical perspective and treats the development of Barbaresco wine making area. Buon weekend!

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