Definition: Champagne tasting

Listen, look, smell, taste. Although the complex phenomena that contribute to these delightful mechanisms of effervescence and foam are not yet fully understood, they play a major role in consumers' fascination with sparkling wines. It must be said that sparkling wines have the particularity of appealing to all our senses: hearing, sight, smell, taste and even touch on the palate and tongue. All the stimuli received by the taster through their ears, eyes, mouth and nose combine to provide a more immediate and intense pleasure than that of a still drink.It is not surprising that, under these conditions, sparkling wines have naturally become the wines of parties and festive celebrations. Sparkling wines are the only ones that can claim to have a sound component. It is initially violent when the bottle is opened, then decreases as the wine is poured, becoming charming and discreet when the foam settles.

In a recent study, Patrice Simard of the University of Compiègne measured the sound emitted by a glass of champagne. These measurements were taken in a special room built inside a building itself constructed on a bed of sand. The floor and walls of this room are covered with a metre of rock wool to prevent any form of reflection. Under these conditions, the room is almost completely silent. This atmosphere is quite special, even unbearable for some people, as the operator inside this enclosure can hear the sound of their own heartbeat and blood rushing in their ears. With the right equipment, it is then possible to record the sound of the wine being poured and then the fizz, by standardising the serving conditions, and then digitise these sounds. After multiple calculations, an image is obtained that allows us to observe how the frequencies of the acoustic signal evolve over time. The audience could easily see that with lemonade, the result is extremely fleeting. The glass is not subjected to much stress. With champagne, the phenomenon lasts several tens of seconds. The detachment of the bubbles, their agglomeration on the surface and, above all, their bursting, excite the mechanical structures of the glass. For the same champagne, the sound recordings are very different depending on the type of glass used.

Roger Douillard and Bertrand Robillard demonstrate that the bubbles in a glass are generated by nucleation sites present in the wine or on the walls of the glass. These sites are either micro-cavities in the glass itself or particles deposited on its surface. These small particles can be atmospheric dust or fabric fibre debris from a cloth. Using a specially treated and cleaned glass, Bertrand Robillard was able to demonstrate that without nucleation sites, there is no effervescence and therefore no foam. As long as these nucleation sites are present and active, they generate successive bubbles, forming a train of bubbles. A nucleation site thus produces 10 to 20 bubbles per second, and we generally observe a few to several dozen bubble trains in a glass. The bubbles rise in the glass under the effect of Archimedes' principle. As they rise, their diameters increase because carbon dioxide diffuses from the wine into the bubble, causing it to grow. These bubbles feed the foam that forms on the surface of the wine. The arrival of a bubble at the surface is a key moment in the life of that bubble. At the surface, two things can happen to the bubble: it can deflate or the liquid film separating it from the air can burst. The bursting of bubbles when they reach the surface of the glass causes fine droplets of wine to be ejected several centimetres. Unlike a drink such as lemonade, where the bubbles burst very quickly, the surface of champagne contains macromolecules known as amphiphilic molecules. These large molecules have oenophilic parts that 'like' wine and other oenophobic parts that prefer to be in contact with gas. These molecules, present at the wine-air interface, stabilise the foam by slowing down or even preventing it from deflating or exploding. Roger Douillard was able to demonstrate on camera that a wine enriched with macromolecules through ultrafiltration has a much better foam retention than the same wine depleted of these same macromolecules. The bubbles that remain on the surface of the glass then migrate towards the rim of the glass, as they tend to combine and stick to the glass wall to form a collar. But this balance is very unstable. Bertrand Robillard illustrates the devastating effect that lipstick or dishwasher rinse aid can have on the foam retention of champagne. However, when a consumer looks at a glass of champagne, they do not necessarily perceive the full complexity of these phenomena. On the other hand, they always feel a certain fascination when watching these movements repeated over and over again in the glass. This fascination is quite comparable to that of flames in a fireplace.

Carbon dioxide makes a significant contribution to smell and taste. However, it must be acknowledged that little research has been devoted to the influence of carbon dioxide on the sensory perceptions of a product. We do know, however, that the oral cavity occupies a very important place in the conscious area of our brain. When an effervescent product is put in the mouth, it provides a very strong stimulation. Carbon dioxide acts in two ways: initially, its action is rather mechanical and instantaneous, like a small prick, then it is prolonged by a chemical effect of the carbon dioxide. However, carbon dioxide is a stimulus for pain fibres, the opposite of pleasure. Care must therefore be taken to ensure that the bubbles are not too prominent, causing a tingling sensation without reaching the point of burning. Work is currently underway to try to understand these mechanisms and explain why, at equal concentrations of carbon dioxide, some wines have an aggressive, explosive effervescence, while others have a softer, more caressing effervescence that harmonises better with the other sensory stimuli provided by the wine.