A few days ago I was admiring a very nice glass that just got filled with sparkling wine. There were lots of steady trains of bubbles, the bubbles were quite fine (small), and they created a very pretty ring that lingered all around the surface of the liquid, in contact with the wall of the glass. In fact, it was a very good case study.
Whatever the method is of getting bubbles in wine, this is the simple principle of effervescence: carbon dioxide, or CO2, is dissolved (trapped) in the liquid. In sparkling wines, the liquid is “over saturated” in/with CO2, creating pressure as the bottle is sealed. The pressure inside a bottle of sparkling can reach 8 bars. The lower the temperature of the liquid, the more soluble the CO2 is. This is one reason why, in addition to make it more pleasant to taste, one might want to keep sparkling wine at cold temperature prior to drinking, so the CO2 does not escape too fast, causing the wine to become “flat” within minutes.
The life cycle of a bubble is as follows: nucleation (birth), ascension and growth, burst (death). Bubbles appear on an immersed particle in the glass, usually dust or fibre residues (from a drying towel), or on a rough surface, like a scratch. Then they rise to the surface of the wine, loading themselves on the way up with more CO2. That’s why bubbles increase in size in their ascent. The composition of the wine affects the bubbles as well, and how the mousse, or foam, on top of the surface behaves. For example, tensio-active molecules, such as proteins, stabilise the gas/liquid interface of the bubbles.
As they eventually burst, they project minuscule droplets that disperse the aromas of the wine. It is important that the wine is poured properly, gently and with the glass inclined to avoid excessive CO2 loss. The glass itself is also very important. Sometimes we hear people complain that a sparkling wine is not fizzy enough, when it’s only a problem with the glass. As a reminder, glasses should be washed with hot water, using as little detergent (if any at all) as possible, thoroughly rinsed with very hot water and left head down to dry. It is likely one will use a towel to get rid of watermarks, and that’s fine. As for the shape of the glass, I recommend quite tall, and not too open on top, so aromas can concentrate and not be dispersed as soon as bubbles burst. Martini-style glasses to be avoided at all costs!
After all this attention, you’ll be able to get more out of the wine, and you’ll enjoy it even more.
Jonathan Médard – Winemaker