Pyrazines

More correctly known by their long name methoxypyrazines, pyrazines are the compounds in grapes that can cause a powerful green bell pepper aroma and flavor. Pyrazines (PEER-a-zeens) are especially prevalent in sauvignon blanc and cabernet sauvignon. They can be greatly reduced by exposing grapes to more sunlight as they ripen. Unripe sauvignon blanc or cabernet can have pyrazine levels off the charts.  Extreme pyrazine levels are generally considered a defect in a wine, although moderate pyrazines are a hallmark of some types of wine–New Zealand sauvignon blanc for example.