Pét-Nat vs. Champagne
Traditional Champagne (and other sparkling wines like Crémant and Cava) are made by combining one or more still dry wines—basically, finished wines that have already undergone fermentation—with a small amount of yeast and sugary liqueur. This combination is bottled and aged, and the yeast eats the sugar in the liqueur. This second, in-bottle fermentation produces the trapped carbon dioxide that gives these sparkling wines their bubbles. (Prosecco and other less-expensive sparkling wines often undergo secondary fermentation in large tanks, rather than in bottles. In some cases, C02 is simply pumped into a finished wine before bottling.)
"Pét-Nat is like a junior version of this really complicated Champagne process," says Steve Hall, co-owner of Spencer, a restaurant and natural-wine shop in Ann Arbor, Michigan. Rather than blending different dry wines and putting them through a second round of fermentation and aging, pét-nat is bottled while still undergoing its first round of fermentation. The French call this process "methode ancestral," and it's likely been around far longer than other, more complex methods of producing sparkling wine.