Would you like pepper with that?
New Zealand Syrah is typically a lot more peppery than Australian Shiraz (same grape, different name). Syrah grown in cool conditions tends to be a lot more peppery than Syrah grown in warmer climates and hotter vintages.
In 2007, the Australian Wine Research Institute (AWRI) identified Rotundone as the compound that produces peppery flavour in Syrah/Shiraz. It’s a very potent compound that most people can detect in concentrations as low as 16 parts in a trillion. One in five people can’t detect Rotundone because they have a blind spot referred to as “specific anosmia”.
Rotundone is found in the skin of the grape and is fairly water soluble therefore is easily extracted during fermentation. There’s a rapid increase in Rotundone levels at the beginning of fermentation. After that Rotundone remains fairly stable, even throughout bottle age.
In 2012, the AWRI chose a vineyard noted for its profoundly peppery wines and mapped the Rotundone levels in a cross-section of grapes. The vineyard is Mt Langi Ghiran (tastings) in the Grampians, a cool climate sub-region in Victoria.
The grapes with the highest Rotundone levels had concentrations that were 15 times higher than those with the lowest levels. Grapes with the lowest light exposure and coolest temperatures were found to have the highest concentrations of Rotundone. It was also lower in the better exposed berries found in the tops of bunches than the more shaded berries at the bottom of the bunch.
Leaf removal helped to lower Rotundone levels, although bunch removal had little effect.