At a Beijing “food and wine exhibition” (which was 95% wine) my favorite drinks were the Lindemans fruity beers — a type of beer called lambic. The label of the raspberry (framboise) one says:
Lindemans Framboise is a lambic made from local barley, unmalted wheat, and wild [= air-borne] yeast.Â After spontaneous fermentation, raspberries are added, creating a secondary fermentation and yielding a beer of exceptional flavor and complexity.
Maybe the presence of two quite different fermentations (grain and fruit) is why it tastes so good, just as this says. To me, the more important point is the linkage of fermentation and complexity — the idea that fermentation creates complexity.