Many white wines undergo a process that causes them to take on buttery flavors (which sometimes come across as buttered popcorn or even butterscotch). That process is called malo-lactic fermentation, and here's the quick take on how it works. Just after the grapes are made into wine, a special type of beneficial bacteria is added to the wine. That bacteria converts one of the acids in wine (malic) to another type of acid (lactic). The two acids feel different on the tongue. Malic acid is very sharp (it's the acid in a Granny Smith apple); lactic acid is fairly soft (it's the acid in milk). Most Chardonnay's go through malo-lactic fermentation and are therefore soft and buttery.