Methoxypyrazines are a class of heterocyclic aromatic organic compounds that are important for the varietal aroma of especially Sauvignon blanc and Cabernet sauvignon (but also other Bordeaux cultivars like Merlot, Cabernet franc and Carmenère). The most important methoxypyrazines that occur in these grapes are 2-methoxy-3-isobutylpyrazine (MIBP, or isobutyl methoxypyrazine), 3-isobutyl-2-methoxypyrazine (IBMP) and 3-isopropyl-2-methoxypyrazine (IPMP). They have a very low detection threshold and are responsible for green, vegetative and herbaceous aromas in the wine e.g. aromas of grass, asparagus, beans and green bell pepper. Although methoxypyrazines confer positive attributes to Sauvignon blanc and Cabernet sauvignon wines, in general they have a negative impact on wine quality of (especially) red wines. In grapes, the accumulation of methoxypyrazines begins at berry set and their concentration starts to decrease again just before or around the véraison. At harvest, the total concentration of methoxypyrazines are still only 5-10% of the maximum concentration before véraison. However, harvesting of underripe grapes may result in higher concentrations of methoxypyrazines and unwanted green aromas in the wine.