Cabernet Sauvignon was planted in the Barossa prior to C1900 though Merlot, a common blending partner, only appeared from the 1980s. Wines labelled as Barossa Valley Merlot appeared after 2000 and the talk at the time was the Barossa was too warm for Merlot. This is because they were compared with those from the type location of Bordeaux, France with a far cooler climate.
As I tell customers ‘judge what is in the glass’ not what you wish it to be. Barossa Merlot is delicious when you ask, is it a good drink. This problem develops because a group of purists want to convince us that each variety only reveals its true pedigree and thus greatest potential over quite a narrow climate range. So when you grow either side of this optimum the result will be lesser.
The problem is the mean for each variety is based on assumptions on European wines and associated climates. I ask customers to reject this absurd idea. Buying well means drinking well.