Sparkling wines are more popular than ever, as they are lively and refreshing. How are they made, and what produces the bubbles?
Where do the bubbles come from?
Sparkling wines have carbon dioxide dissolved under pressure . When the bottle is opened, the pressure is released and the gas starts to evaporate. Bubbles form on irregularities on the glass, or material suspended in the wine.
What if there are no bubbles?
The main reason for bubble-free sparkling wine is dirty glasses. There is nowhere for the bubbles to nucleate.
What is the gas pressure within a bottle?
Champagne usually has a pressure of around 6 bar – 6 x atmospheric pressure – at room temperature. Which is why you get a mess if you open a warm bottle. The pressure decreases rapidly as the wine is chilled, which is one very good reason for serving cold Champagne. Other sparkling wines have a similar, or lower pressure.
Where does the carbon dioxide come from?
When sugar ferments in the presence of yeast, it produces alcohol and carbon dioxide. The more sugar you have, the more alcohol and carbon dioxide is produced.
- In most sparkling wine production, grapes are fermented to a still wine. Sugar and yeast are added, and the second fermentation produces carbon dioxide for the sparkle.
- In some rare cases there is just one fermentation, and the carbon dioxide retained, rather than allowed to evaporate.
- The cheapest way of introducing the gas is to inject it into still wine, but this produces a coarse result.
Producing bubbles using a second fermentation
Starting with a still wine, there are three main methods for producing the bubbles:-
- The method used in Champagne, now generally known as the ‘traditional method’. Wine is put into a bottle, along with sugar, yeast and nutrients. This second fermentation produces carbon dioxide. The debris is removed, and the wine sold in the same bottle.
- The transfer method, in which secondary fermentation is in a bottle, but the wine is then transferred to a vat, where the debris is filtered out. The wine is sold in a different bottle.
- The Charmat or Tank Method, where the second fermentation is carried out in tanks. The wine is then filtered and bottled under pressure.
The quality factor
Quality sparkling wines undergo a number of processes and maturation to give the same depth and complexity as a fine still wine, but they also have the prickle of bursting bubbles on the tongue.