Pyrazines

What Are Pyrazines?

Pyrazines are nitrogen-containing aromatic compounds that occur naturally in certain grape varieties and produce characteristic "green" aromas. The best-known variant is methoxypyrazines (IBMP, IPMP, SBMP), which are responsible for notes of green pepper, freshly cut grass, green beans, and herbs.

Occurrence in Grape Varieties

Pyrazines are found mainly in:

• Cabernet Sauvignon: Green pepper, especially in cooler climates
• Sauvignon Blanc: Gooseberry, grass, green pepper
• Cabernet Franc: Herbaceous, green notes
• Merlot: To a lesser extent, primarily when under-ripe

How Do Pyrazines Form?

Pyrazines are produced mainly in the grape skins and concentrate there during the early growth phase of the berries. As ripeness increases, and particularly during véraison (colour change), pyrazine concentrations decrease.

Factors That Influence Pyrazines:

Increase concentration:

• Cool climate or cold vintages
• Shading of the grapes by excessive leaf cover
• Early harvest before full phenolic ripeness
• High yields (diluted ripeness)

Reduce concentration:

• Warm to hot climate
• Sun exposure to the grape zone
• Full physiological ripeness
• Leaf removal and crop thinning

Flavour Perception

Pyrazines have an extremely low perception threshold – even tiny amounts (a few nanograms per litre) are clearly perceptible in wine. This makes them a dominant aromatic feature when present.

The typical aromas are:

• Green pepper (bell pepper)
• Freshly mown grass
• Green beans
• Asparagus
• Herbaceous, vegetal notes

Desirable or a Fault?

The assessment of pyrazines is context-dependent and a matter of taste:

Positive (terroir marker): In moderate amounts, pyrazines are considered part of the authentic character of certain wines. Classic Bordeaux wines or cool-climate Cabernets often show subtle green notes that are valued as elegant and typical – especially in combination with ripe fruit.

Negative (under-ripeness): Dominant pyrazine aromas that obscure the fruit are regarded as a sign of insufficient grape ripeness. In the New World, where warmer climates allow full ripeness, green notes are often seen as a wine fault.

Reducing Pyrazines

Modern vineyard management often aims to minimise pyrazines:

• Leaf removal: Increasing sun exposure to the grape zone
• Yield reduction: Fewer grapes = better ripeness
• Later harvest: Waiting for full physiological ripeness
• Clone selection: Modern Cabernet clones have lower pyrazine levels

Conclusion

Pyrazines are a fascinating example of how chemical compounds shape wine style. They are neither inherently good nor bad – their acceptance depends on balance, context, and winemaking philosophy. In moderation they can lend complexity and freshness; in excess they make a wine taste under-ripe and vegetal.