They are the carbon dioxide produced during a second fermentation that occurs either in the bottle (Champagne or Classic Method) or in pressurized vats (Charmat or Martinotti Method).
(The third possibility is “Coca-Cola” sparkling wine made by simply adding fizz. I urge you to avoid it).
Sparkling wine (called Vino Spumante or Vino Frizzante in Italian) was discovered by accident when wine that had fermented and had been bottled in cold cellars during the fall began fermenting again with warm temperatures in the spring. The wine got fizzy, and the bottles often exploded. Not what any winemaker wanted.
But one day in the late 17th century, a French monk named Dom Pierre Pérignon supposedly called out, “Come quickly, I am tasting the stars!” He didn’t “discover” champagne, but he recognized its potential, developed stronger glass bottles, clarification techniques and a better corking system.
According to the “Champagne or Classic Method”, the wine ferments once in vats then a second time in the bottle. It rests on the spent yeast, or lees, for at least 18 to 80 months.
Then, the bottles are set at an angle and turned (“remouage” in French) a quarter turn a day, a method famously developed by the Widow Ponsard Cliquot, the Veuve Cliquot, when she needed a faster method to get her champagne ready at the end of the Napoleonic Wars. (She managed to keep it a secret for ten years by profit sharing with her workers.)
Some wineries still use these traditional “pupitres” and some have mechanized systems. Once the yeast descends into the bottleneck, the winemaker performs “degorgement” where the bottle is opened, the spent yeasts pop out and the bottle is quickly re-corked.
In the early 1960s, Franco Zilliani, pioneered Italian sparkling wine made with traditional Champagne grapes (Chardonnay and/or Pinot Noir) using the Classic Method near Brescia, in the hills northeast of Milan. I met Zilliani at my graduation from sommelier school.
In the last forty years, the Classic Method has been used all around Italy to make sparkling wine with many grape varieties, not just the traditional Chardonnay and Pinot Noir. This fall, I tasted fabulous “Metodo Classico” in Sicily, for example, at Porta Del Vento (Cattarato grapes), Marco De Bartoli (Grillo) and COS (Frappato).
What about Prosecco?
As in France, the age old tradition for making sparkling wine with Prosecco grapes in the Veneto was similar to the Classic Method in that the wine fermented for the second time in the bottle. The difference was that the spent yeasts were left in the bottle (“Col Fondo” in Italian or “Sur Lie” in French).
In the seventies, Prosecco makers in the Veneto widely adopted the “Charmat or Martinotti Method” of making Prosecco by doing the second fermentation in pressurized vats so the yeasts could easily be siphoned off and the wine clarified. (This method had been developed in Asti in Piedmont for making sweet sparkling wine made with Moscato grapes). Some Prosecco makers also began sweetening the normally dry wine during the second fermentation.
In the last twenty years, winemakers in the Veneto have tended toward making drier wine and have begun going back to the traditional way of making Prosecco “Sur Lie” (see post on Case Coste Piane) or “Col Fondo” (see post on Bele Casel).