THE CONSENSUS IS THAT OLD VINES – a hazy term not defined anywhere except in the Barossa (but generally meaning plants at least 20-30 years old) – make the best wine. True? Kind of. Gnarled, twisted old grapevines, because of their much-reduced yields (vineyards’ output peaks at around 20 years, after which it declines with each vintage), do give more concentrated, flavoursome juice than their younger, more vigorous fellows. Terroir enthusiasts claim, too, that mature vines’ deeper roots suck much-prized ‘minerality’ into wines (an assertion that hardcore scientists dismiss as baloney). All said, the key to wine quality is, probably, restricting yields – which can be achieved many ways – and not just by the ‘old vines’ route.