Factors influencing rotundone levels in wines

ROTUNDONE FACTS:

• Rotundone was first identified in 2008 by Australian researchers as the aroma compound present in Shiraz wines responsible for the peppery character.
• It forms part of the terpene family and is classified as a sesquiterpene.
• Rotundone is also the main aromatic compound found in white and black pepper.
• It is also found in various other herbs and spices in nature such as thyme, oregano, rosemary and basil.
• It has a sensory threshold of 16 ng/L in red wine.
• Rotundone has subsequently been identified in various other grape varieties above sensory threshold: Duras, Durif, Mouvèdre, Gamay noir, Schioppettino, Vespolina and Gruener Veltliner.
• It can also be found in various other grape varieties such as Pinot noir and Cabernet Sauvignon, but usually in concentrations below the sensory threshold.
• Concentrations of rotundone differ between different clones of the same cultivar.
• The highest concentration reported for Shiraz is 620 ng/kg grapes. Highest concentration reported for rotundone in all grape varieties is 5440 (+/- 33) ng/kg for Vespolina grapes.
• Rotundone concentrations in final wines are usually much lower than the initial concentration in the grapes.
• Rotundone is very flavour active and very stable in wine over time.
• It is a hydrophobic molecule and extraction is improved by the formation of alcohol during fermentation.
• Rotundone is located in the grape skins (only), leaves, petioles and peduncles/rachises.
• Leaves contain the highest concentration of rotundone followed by petioles, peduncle/rachises – whole bunch fermentation will increase rotundone levels in wine.
• Rotundone is produced locally in the specific plant tissues and is not translocated via the phloem to berries.
• Herbivore attack does not have a major effect like in the case of other terpenes.
• Powdery mildew promotes higher rotundone levels in Duras grapes.
• Botrytis infection reduces rotundone levels.
• Rotundone is more abundant in cooler climates or years.
• Temperatures above 25°C have a negative impact on rotundone concentrations in vines.
• Rotundone concentrations are higher in shaded bunches than bunches exposed to direct sunlight.
• Rotundone is derived from a pre-cursor α-guaiene and conversion starts at veraison and increases until approximately 44 days after veraison after which the concentration stays stable.
• The most rapid rotundone accumulation is two weeks before harvest.
• Increased water balance / irrigation from veraison to harvest increases rotundone levels in the vine.
• Precision irrigation and canopy management strategies can increase rotundone concentrations.
• People differ in their sensitivity for rotundone with 20 – 25% of the general population being anosmic to it.