When we pop the cork of a sparkling wine at a party a flurry of bubbles are released. We love sipping those bubbles, but how do they get in the bottle? There are several ways that it can happen.
Sparkling wine is bubbly because carbon dioxide gas, a byproduct of fermentation, is trapped within the wine. During fermentation yeast feeds on the grape juice’s natural sugars and produces heat, alcohol, and carbon dioxide. During the initial fermentation, this gas is released into the air. When wine is allowed (or encouraged!) to undergo a second fermentation within the bottle the carbon dioxide gas is trapped inside in the form of bubbles.
The following methods are a few different ways to produce bubbles in a bottle of wine. There is a lot more information behind each of these techniques, but this is a good start to get the general idea. We’ll start with the oldest method and move forward through time and technological advances.
In this ancient method, a wine is bottled before it has fully completed the first fermentation. The wine is bottled while the yeast is still alive and kicking. Once in the bottle, the yeast continues to feed on the remaining sugars in the wine, releasing carbon dioxide that is then trapped in the bottle. This produces a wine that is fizzy rather than seriously bubbly, and the resulting wine is usually a little bit sweet. Méthode Ancestrale wines are also normally somewhat cloudy. This is because the spent yeast (or lees) remains in the bottle as sediment. This method is not used commonly these day, but can be found still in some parts of France, most notably the Jura and Savoie. We often carry wines fermented in this style – right now we have Bornard Tant-Mieux from the Jura at our South End location. It is pink, somewhat sweet, fizzy and really delicious!
Méthode Traditionnelle or Traditional Method:
The “traditional method” is the one used in the Champagne region, and in many other places where high quality sparkling wines are made. It is a complex, time-consuming practice, which is part of the reason why Champagnes are more pricy than sparkling wines made by other methods. Here we start with a base wine that has completely fermented. Yeast and unfermented grape juice are added to this wine and the wine is placed in thick bottles with crown caps. When the yeast begins to feed on the sugar in the added juice a secondary fermentation begins. Eventually, the yeast runs out of food and dies, leaving lees behind. The longer a wine rests on these lees, the more flavor and complexity it will absorb from them. Lees impart a delicious bready, yeasty or brioche-like flavor and aroma, and can also add a richer mouthfeel.
When a winemaker decides that a wine has aged on the lees long enough, they will begin riddling the wines. Riddling is the first step in removing that lees sediment so the finished wine won’t be cloudy. Traditionally bottles are slowly, day by day, tilted from a horizontal position to a vertical position with the neck of the bottle facing down. When done by hand this is a very slow, very labor-intensive process that can take up to six weeks. With each daily adjustment, the bottle is given a slight shake to move the sediment down toward the neck. When all of the sediment has settled in the neck it is time to remove it or disgorge the wine. Most commonly, the neck of the bottle is frozen. This allows the person disgorging the wine to open the bottle upside-down, pop out the frozen plug of sediment, and then quickly flip the bottle back to an upright position. Exciting!
Now the sediment is gone but so is a bit of the wine! At this point the winemaker tops up the level of wine in the bottle with some extra still wine and (if desired) a bit of sugar to balance out the wine’s acidity. (A non-dosage sparkling wine is one in which no extra sugar is added, ensuring a very dry wine.) At this point the bottles are corked and a little metal cage is clasped over the top to keep the cork from popping out under the pressure of the carbon dioxide gas. This is why you should never remove the cage from the top of a bottle of bubbly until you’re ready to take the cork out!
All of our Champagnes are made with this method as are some of our bubbly wines from other places like the Chateau Tour Grise Brut Non-Dose from the Loire Valley and the Schloss Gobelsberg Brut from Austria.
In this method, used more for inexpensive wines that won’t be aged, the second fermentation is induced in the base wine in a closed bulk tank instead of in each bottle. With this method the fermentation can be stopped whenever the winemaker desires, at whatever atmospheric pressure they want, by lowering the temperature of the tank. The wine is then clarified and sometimes sweetened, and bottled using a pressure filler to keep the carbon dioxide in. Wines made in this method will have larger bubbles and the bubbles won’t last as long. This is much less labor-intensive and time-consuming, and thus a less expensive means of production than the traditional method.
Last and Least – Simple Carbonation:
Wine can also be carbonated the same way soft drinks are. With this method carbon dioxide is pumped into the tank of wine and then the wine is bottled under pressure. This method makes very large bubbles that fade very quickly, and it’s the cheapest and by far the fastest method of inducing bubbles.
Note: this post is part one in a series focusing on sparkling wines – part two focuses on the history of Champagne and the differences between récoltant-manipulants and négociant-manipulants and part three focuses on small grower and Champagne maker Alexandre Chartogne.
Julie Cappellano is the General Manager and wine buyer at Formaggio Kitchen South End, Boston.