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Publish at April 12 2022 Updated April 21 2022

The mysteries of old wines [Thesis].

Approaches to the aging bouquet of great Bordeaux wines

"The wine is the land. This one is slightly gravelly, it's a Medoc. The wine is also the sun. This wine benefited from a beautiful southwestern exposure on a hillside with a good slope." Louis de Funès, in "The Wing or the Thigh". See the video here.

This tasty scene from "The Wing or the Thigh" takes us to the heart of Justine Laboyrie's thesis on the age-friendly qualities of great Bordeaux wines.

We know, either from direct experience or from seeing it in films, that there is a strong social ritual of tasting great wines. We know less about what exactly this ritual corresponds to, which this research allows us to visit through its aromatic and molecular aspects.

Wine for aging and bouquet for aging

The Bordeaux region produces 700 million bottles per year, more than half of which goes for export. The knowledge of the specificities of the great wines of Bordeaux is such a challenge that the details of the results are under the seal of confidentiality.

If substantial parts of the thesis are absent, there is nevertheless enough to enter into the knowledge of the mechanisms that make great wines.

A wine suitable for aging is called a vin de garde. It is a "first wine," a great wine. Second wines do not have this destiny of being able to be kept. Aging is specifically about the evolution of aromas in the bottle, away from oxygen.

Then it is a matter for the winemaker to lead the aromas towards the expression of the "bouquet of ageing."

"Emile Peynaud, a great Bordeaux oenologist, described this bouquet as "a mixture of complex scents that the aged wine exhales in the glass, translates into a melting, an olfactory binding. The evolution of wine into bouquet is one of the most impressive phenomena in oenology and one of the least understood"."

The importance of terroir

Bordeaux is a territory in southwestern France where vineyards are attested to as early as the first century AD. The Celtic people of the Bituriges Vivisques (nothing to do with " taking a biture "...) from Bourges founded Burdigala, ancestor of Bordeaux.

The ancestor of Cabernets is, moreover, the "biturica" grape variety, more adapted to the region than the first vines originating from the Mediterranean.

The terroir (vine, soil, and climate), which the thesis shows is involved in the genesis of the aging bouquet, is related to the rivers that delineate three spaces: the left bank, the right bank, and the entre-deux-mers (between the Garonne and the Dordogne).

The soils here are gravelly, calcareous, clayey, or sandy. The ability of the soil to transform organic nitrogen into mineral nitrogen has an effect on the aromatic quality of the wine.

Similarly, climate change issues are of crucial importance for the production of great wines, which are sensitive to good water harmony.

Wine aromas

The aromatic component of wines comes from nearly 800 volatile organic compounds, a small portion of which are above olfactory detection thresholds...

The sources of these aromas are numerous and are related to the metabolism of the wine, to fermentation, to reactions produced during winemaking, to interactions with aging containers (barrels), and to chemical reactions during aging (in the bottle, that is).

A quality wine is recognizable by its complexity, its balance between the acid, sweet, and bitter dimensions, its length in the mouth, and its ageing potential.

Strategies for obtaining a great wine

The quality of wine depends on the following characteristics:

  1. Grape quality:influence of terroir, ripening period (followed by tasting of berries: pulp, skins, seeds), oenological ripeness parameters.

  2. Aromas present in wine.
    "Aromas evolve and sometimes are revealed after several years of aging. Flavors are formed during aging due to molecules of interest released from precursors or born through chemical reactions from other compounds."
  3. The proper conduct of fermentations (alcoholic with yeast, then malolactic for almost all red wines).
    "The winemaker must transform the grape into wine."
    This is a perilous exercise that requires "sensitive, selective and partial extractions" during the alcoholic fermentation and the vatting phase.

  4. The aromas present in young wine.

  5. The maturation of wines in barrels. This process stabilizes and fixes the potential of the wine. The barrel is heated, oxygen passes through the wood in a minute way and causes reactions. The wood in the barrel provides its aromatic dimension.

  6. Bottle aging in a "reducing" (oxygen-reduced) environment. New compounds are formed at the origin of the aging bouquet. At this stage there is an evolution of aromas and the revelation of other aromatic compounds in a slow manner.

  7. The mode of service (aeration, rotation in the glass) has a great importance for the aromatic expression of great wines.
    "The [dimethyl sulfide]DMS is a so-called light sulfur compound [...], its volatility is high and this implies that the olfactory contribution of DMS to the aromatic expression of wines is dependent on the mode of service and the temporality of tasting. "

Sensory and molecular analysis

The author identified the main odors revealed by the grands crus: fresh, red and black fruits, undergrowth odors, truffle, licorice, minty odor, woody, spicy. She then conducted an analysis of the molecules important to the aging bouquet.

"Studying aging compounds involves paying attention to molecules that are found in aged wines, but that may originate in the grape. "

We'll read about terpenes, minty-smelling compounds, and the dimethyl sulfide DMS. The latter, already mentioned above as a reason for the importance of the mode of service, is the subject of an entire section of the thesis. The aromas involved in old wines are often involved in the fruit component of the wines.

"Work has been addressed for compounds with "menteous" odors, but the identification of a precursor common to all of them was not successful in the time available."

A strong Dionysian DMS

Let's go back to DMS. It is present as a precursor in young wine.

By complex actions, it promotes aromatic notes, then inhibits them "successively and repeatedly alternately". The author speaks of "sensory polymorphism that would explain its strong correlation with the level of complexity of wines".

"Once released into wine, DMS contributes to many odorant expressions. The matrix in which it is found, its concentration, and its ability to interact with volatile and nonvolatile components are the site of a sensory polymorphism that may participate in the "fascinating" character of the bouquet."

So, in the back cover of his book on Dionysus (Bacchus), Dionysus in the open, the Helenist Marcel Detienne questions:

"When Dionysus emerges on the Greek stage, the multiple always accompanies him. Diverse, unpredictable, how can he be recognized? The mask that conceals him is also the one that reveals him. His appearance is made of incessant games, of presence and absence, his identity remains indefinitely that of equivocation."

Illustration: janeb13 from Pixabay, The Triumph of Bacchus, Velázquez.

To be read:

Justine Laboyrie, Composition and origin of the ageing bouquet of Bordeaux red wines. Influences of terroir in the aromatic expression of aged wines. Human medicine and pathology. University of Bordeaux, 2020.

Thesis available for consultation (in its disseminable version) on: https://tel.archives-ouvertes.fr/tel-03213152


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