Aroma Compounds
/Pyrazines
Have you ever smelled a glass of red wine and experienced the surprising scent of grass or bell pepper? Has anyone ever described a glass of wine as being vegetal? When that happens what you are really smelling are the Pyrazines, which are organic compounds in the stems, leaves, and unripe berries of grapes. While Pyrazines are present in the grapes themselves, they begin to lose their strength during veraison and are generally eliminated when the grapes are fully ripe. It is generally believed that Pyrazines are a defense system for the grape, preventing it from being consumed before it is fully ripe and the seeds are ripe enough for successful germination.
The Winemaking
Grapes undergoing veraison and losing the strong Pyrazine characteristic
Vegetal flavors in a wine are hit or miss depending on the wine drinker's palate. Some winemakers choose a stronger fruit flavor and higher alcohol content and leave their fruit on the vine to ripen to a point where there are no Pyrazines left to alter the flavor of the wine. Many winemakers feel that vegetal component adds a deep complexity to their wine and they go to great lengths to preserve some of its characteristics. Further still, the presence of Pyrazines is often a regional characteristic with darker or colder regions struggling to ripen the grapes enough to eliminate the Pyrazine flavors. This is why you don't see Cabernet Sauvignon grown and produced successfully in colder climates.
The Result
Pyrazines help us to know our bottle of wine. When you are considering buying a red wine made from Bordeaux grape, read the back of the label and see where it was made. Is it generally sunny or generally cold? If it's dark and cold, then you know your bottle may have some vegetal characteristics to it. So the next time you smell bell pepper or asparagus in your red wine, have a cheers to the Pyrazine and enjoy its unique characteristics.