What are these "pét-nat" sparkling wines my hipster wine friends keep talking about?

Dear Dr. Vinny,

What are these "pét-nat" sparkling wines my hipster wine friends keep talking about?

—Jordan, Williamsburg, N.Y.

Dear Jordan,

"Natural" wines seem to be all the rage among a certain, ahem, "hip" segment of the market these days, and pétillant naturel wines are the bubbly equivalent (it literally translates to "natural sparkling").

But this trendy new thing in sparkling wine is actually so old that the term for the winemaking technique is méthode ancestrale, a much simpler but less controlled method than the now common méthode traditionnelle practiced in Champagne. For a very long time—centuries, perhaps—carbonation was an accident of winemaking: Fermentation would halt when it got cold in the winters of regions like Champagne, only to restart—after the wines had been bottled—when the springtime awoke the slumbering yeasts, causing a secondary fermentation that gave the wine its bubbles.

Today, pét-nats, as they're nicknamed, are made by stopping an unfinished fermentation and then bottling the wine before allowing the fermentation to complete, a risky and unpredictable technique resulting in a sometimes-cloudy wine that's fizzy but less bubbly than traditional modern Champagnes. The pét-nat method is not limited to a specific region, but leading areas include the Loire Valley, Savoie and Limoux in France, and Italy, where Prosecco pét-nat practitioners call it "col fondo."

And like hipsters and their telltale beards, you can usually spot a pét-nat by its crown cap in lieu of a cork.

—Dr. Vinny