Thiols, terpenes and pyrazines

We can all remember a wine’s unique nose, the subtle blend of different aromas to create a perfect alchemy. These many and varied aromas come from three different origin points. Primary or varietal aromas are created by the vine within grapes’ pulp or skin. Secondary aromas are the result of the metabolism of the micro-organisms (yeast, bacteria) responsible for alcoholic and malolactic fermentation. Tertiary aromas are created during a wine’s maturation and its development in bottle. They are the result of the chemical and biochemical transformation of primary and secondary aromas.

As their name suggests, the varietal aromas synthesised by the vine depend on the grape variety. The three families of aromas are thiols, terpenes and pyrazines.

• As their name suggests, the varietal aromas synthesised by the vine depend on the grape variety. The three families of aromas are thiols, terpenes and pyrazines.
• Varietal thiols are sulphur molecules that are highly sought after in certain white and rosé varieties such as Sauvignon or Syrah. These molecules appear as precursors in the grape and are revealed during fermentation by the action of yeast. Their characteristic, distinctive aromas come from the molecules 3MH (grapefruit, citrus and exotic fruit), A-3MH (boxwood and tropical fruit), and 4MMP (boxwood). The quantity of thiols made by the plant is affected by the soils, the climate and the cultivation method. Depending on the terroir, Sauvignon Blanc expresses varietal thiols in varying proportions, supplemented by pyrazic elements.
• Terpenes are a large family covering more than 4,000 compounds. These compounds, including rose-like aromas, play a major role in the nose of wines from the Muscat family, as well as the aromas of certain Alsatian and German grape varieties (Gewürztraminer, Pinot Gris, Riesling, etc.). These aromas are present in free, aromatic form in the grape, in odourless form linked to a sugar. These terpenes can be released chemically or enzymatically during fermentation.
• Each grape variety has a genetic heritage that is conducive to expressing particular aromas, but there is a wide range of aromas even from the same grape variety. This range can be found between and within different production regions. Hence the long-standing daily work of matching plants to their environment in order to obtain wines that express the grape variety’s aromatic potential to the full.