The great wines of Burgundy, Alsace, Loire, Northern Rhone, Barolo, Mosel, Austria, Hungary and Slovenia use only one grape variety, while those of Bordeaux, Southern Rhone, Languedoc, Rioja, Ribera del Duero and Portugal are blended from many grape varieties. One can easily draw a line separating the blenders from the purists… but the line is not straight: neither geographic latitude nor Winkler index (GDD) correlate to this distinction. What if it all came down to how hazy the sky is?
Looking at a map of the great European wine areas – those with a not too recent history of superb winemaking – one could easily draw a curved line separating the generally more northern areas, emphasizing the purity and completeness of single varietal wines, from the southern areas, whose wines achieve comparable complexity by blending several grape varieties. The line is curved, because climate is influenced not only by latitude but also by winds, seas, microclimates, etc.. This paper results from a speculative but reasoned inquiry to see if I could identify a climate parameter that correlated well with the distinction between blending areas and single varietal areas.