An interesting co-explanation for the prevalence of beer in southern parts of this belt is the relatively weak cultural influence of the Roman Empire on these places. The Wine Belt indeed conforms to a large extent with the territory formerly occupied by Rome, with notable exceptions in areas with large Slavic or Germanic migration (the Balkans, southwestern Germany, northern France respectively), where beer predominates (although often overlapping with wine).
The Vodka Belt occupies what’s left of Europe, to the east and north: