During fermentation, yeast eats up the sugars present in the grape juice, converting them into alcohol. It's like a little party in the wine tank, where the yeast is the guest of honor, and it gets to eat all the sugar it wants. But, some wines are left with a bit of residual sugar, which can make them taste sweeter.
In the case of Pinot Noir, the fermentation process is usually allowed to go all the way, leaving very little residual sugar behind. This is why Pinot Noir is often described as crisp and dry, with flavors that are more earthy and less fruity. But, don't worry, it's not all about the sugar content - there are plenty of other factors that make Pinot Noir so interesting.
For example, the terroir of the region where the grapes are grown can have a big impact on the flavor of the wine. It's like the wine is absorbing all the flavors and characteristics of the surrounding environment, kind of like how a sponge soaks up water. This means that Pinot Noir from different regions can taste completely different, even if they have similar sugar content.
Compare Sugar in Chardonnay to Sugar in Pinot noir