PĂ©tillant-Naturel (Pet Nat) predates Champagne by hundreds of years! Back in 1531, Monks in France bottled and corked fermenting wine in the winter, when the yeast cells were cold & inactive.
Come summer, those yeasts reactivated and fermented the remaining sugars - creating CO2 as a natural by product. This CO2 would be trapped in the bottle & cause the wine to sparkle!
So, unlike Champagne, where winemakers take a wine that has finished fermenting and add sugar to the bottle, natty winemakers prefer the original approach to bubbles – bottle a wine mid fermentation & see what happens.
Some Pet Nats have a slight spritz, while others explode out of the bottle – so open carefully!