The effervescent bubbles in sparkling wine are a result of a fascinating process known as fermentation. As a sommelier and brewer, I have had the pleasure of witnessing this magical transformation firsthand. Allow me to take you on a journey into the world of sparkling wine, where yeasts work their enchantment to create those delightful bubbles.
At the heart of the process lies the yeast. These tiny microorganisms, particularly strains of Saccharomyces cerevisiae, are responsible for the fermentation that occurs in the winemaking process. When yeast comes into contact with sugars present in grape juice, it begins to feed on these sugars and converts them into alcohol and carbon dioxide. It is this carbon dioxide gas that creates the effervescence in sparkling wine.
The process of fermentation occurs in two stages. First, primary fermentation takes place in a closed vessel, such as a stainless steel tank or oak barrel. During this stage, yeast consumes the sugars, producing alcohol and carbon dioxide as byproducts. However, in sparkling wine production, the winemaker deliberately stops primary fermentation before all the sugars are consumed, leaving residual sugars in the wine. This is done to retain a slight sweetness in the final product.
After primary fermentation, the winemaker initiates the second stage of fermentation, known as secondary fermentation, which is crucial for creating the bubbles in sparkling wine. To achieve this, the winemaker adds a mixture known as “liqueur de tirage” to the base wine. This mixture contains a small amount of sugar and yeast, which kickstarts the fermentation process again.
The secondary fermentation occurs in a sealed container, such as a bottle or a pressurized tank. As the yeast consumes the added sugar in the liqueur de tirage, it produces alcohol and carbon dioxide. However, unlike during primary fermentation, this time the carbon dioxide cannot escape into the atmosphere due to the sealed container. Instead, it remains trapped inside the wine, forming bubbles.
The trapped carbon dioxide gradually dissolves into the wine, creating a state of equilibrium. When the bottle is opened, the sudden release of pressure causes the dissolved carbon dioxide to come out of solution, resulting in the effervescent bubbles that we associate with sparkling wine. This process, known as nucleation, is why we hear that delightful “pop” when opening a bottle of Champagne or sparkling wine.
It is worth noting that the pressure inside a bottle of sparkling wine is quite high, typically around 5-6 atmospheres. To withstand this pressure, the bottles used for sparkling wine production are generally thicker and sturdier than those used for still wines. This is why you may notice the distinctive shape of sparkling wine bottles, with their thicker bases and often pronounced punt.
The bubbles in sparkling wine are a result of the secondary fermentation process, where yeast consumes added sugars, producing alcohol and carbon dioxide. The trapped carbon dioxide creates the effervescence in the wine, and when the bottle is opened, the pressure is released, causing the dissolved carbon dioxide to form bubbles. It is this process that adds a touch of magic and joy to every sip of sparkling wine, making it a truly special and celebratory beverage.