Sparkling wine can be produced using different methods, and this affect the quality of the bubbles, which are one of the criteria used to judge the quality of a sparkling wine.
First, we need to understand how sparkling wine is made and how the bubbles are created. The method used to make champagne is called the méthode champenoise, or the champagne method. The base wine, made from primary fermentation (the first fermentation that converts grape juice to wine), is bottled with the addition of a dose of sugar and yeast. The bottle is then sealed with a crown cap and left for secondary fermentation. Because the bottle has been sealed, carbon dioxide, a by-product of fermentation, cannot escape. Instead, it dissolves in the wine. The pressure inside the bottle is around 5–6 bars (approximately three times the pressure of a car tyre). The bottle is left undisturbed from a few months to a few years depending on the wine style. When it’s time to disgorge, the bottle is slowly turned upside down so that the dead yeast cells and sediment, called lees, are pushed to the neck. The neck is then frozen and the crown cap removed. The pressure inside the bottle forces out the frozen lees and the bottle is resealed with a cork.
The bubbles in sparkling wine produced by this method are the smallest, finest and most persistent. In addition, the more time the wine stays in contact with the lees (i.e., ageing in the bottle before disgorging), the finer and more persistent the bubbles. Most wine-producing countries create sparkling wines made using this method, including Crémant (France), Cava (Spain) and Cap Classique (South Africa). You can identity these wines from the labels – either “méthode champenoise” (champagne method) or “méthode traditionelle” (traditional method) will be stated.
The second method of making sparkling wine is called charmat, where secondary fermentation takes place in large stainless-steel tanks under pressure. Following fermentation, the wine is filtered and bottled under pressure, so the dissolved carbon dioxide is trapped in the bottle. The pressure inside the wine is lower, around four bars, and the bubbles created are slightly bigger. Sparkling wines made using this method include Prosecco and Asti from Italy and most Sekt from Germany. This style of sparkling wine is less expensive than its counterpart made in the traditional method, but this doesn’t mean it’s lesser quality. However, this style of wine emphasises the freshness rather than the complex aroma of sparkling wine aged with lees, so it is not meant for ageing.
The third method involves carbonation or a carbon-dioxide injection. The wine does not undergo secondary fermentation but, instead, carbon dioxide is injected into it, similar to making soda. In this case, the bubbles are big and coarse and dissipate quickly. This is the cheapest way of making sparkling wine.
As a rule of thumb, the smaller, finer and more persistent the bubbles, the more complex the sparkling wine. However, we also need to bear in mind that an old sparkling wine, even though it is top quality, will have less bubbles because the dissolved carbon dioxide has slowly escaped through the cork. I recently tasted a nearly 40-year-old sparkling wine from Villiera in South Africa. Although the bubbles had largely disappeared, the wine still tasted fresh and lively.
Glassware plays a significant role in the creation of bubbles. The ideal glass is a long, narrow flute where the bubbles can be seen rising steadily from the bottom to the top, forming a string of beads. More importantly, the bubbles burst when reaching the surface, thus releasing the trapped aromas for us to smell. The wide mouth of a short coupe is not as good for sparkling wine because the bubbles rise to a large surface area and burst and the trapped aromas dissipate quickly.
Interestingly, the glass cannot be too perfect. The tiny scratches, dust and fibres on the inside surface of a glass actually act as bubble-formation sites. The smoother and cleaner the glass, the more difficult it is for bubbles to be formed.
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