That’s easy. Methode champenoise, the incredibly labor intensive, time-consuming, traditional French technique for making fine Champagne. Among many other steps, this involves a second fermentation and at least three to five years aging in the bottle before the final steps of wine making.
All this costs money which is why great sparkling wine is more expensive than sparklers made the “industrial” way. Is there a real difference? Try a methode champenoise sparkler next to one that’s not. And let us know which you like best!