Why Some Wines Smell Like Green Bell Peppers

What are pyrazines?

Pyrazines are a nitrogen-containing compound. They are a type of varietal aroma, meaning they originate in the grape berries in the vineyard.

A green bell pepper dressed up as a queen to show that this aroma is the “Pyrazine Queen.”
Drawing by Anna Sprenger

The most distinctive pyrazine smell is green bell pepper. The compound responsible for this smell is IBMP, which is the shorthand name for 3-Isobutyl-2-Methoxypyrazine.

Besides green bell peppers, pyrazines can also have a leafy green, broccoli stalk, or pea pod smell. Pyrazines are really odorous compounds; it only takes in the order of 2 parts per trillion for human noses to be able to detect the green bell pepper odor that comes from IBMP.

Which wines have pyrazines?

Cabernet Sauvignon, Cabernet Franc, Merlot, Carménère, Malbec, and Sauvignon Blanc.

Basically, anything from Bordeaux is going to have some green pepper smell, especially Left Bank blends dominated by Cabernet Sauvignon. Sauvignon Blanc from New Zealand will also have this aroma. A good rule of thumb is that wines from cooler climates will have more of these green, vegetal flavors (keep reading to find out why!)

How does IBMP form?

A diagram shows two hypotheses for how IBMP originates (one in the leaves and one in the berries).
Two theories about the origin of IBMP in grapes from Lei et al, 2018

There are two contrasting hypotheses about how IBMP forms. One thought is that it originates in the leaves of the vine and then travel to the berries via phloem vascular tubes, the tubes that carry and distribute nutrients throughout plants. The other thought is that it originates in the berries themselves. Maybe it’s a combination of both!

How can we manage vegetal aromas in the vineyard?

Managing the intensity of pyrazine aromas in wine can be done by playing with sunlight exposure at the right time.

A cluster of grapes at véraison with some green berries and some red berries.
Berries changing color at véraison (Photo by Rohit Tandon on Unsplash)

Berries that get a lot of light before they change color (the growth period called “véraison”) tend to have lower IBMP levels. This is because sunlight is thought to photochemically degrade IBMP in green berries. So, removing some leaves around the grape clusters and exposing them to sunlight before véraison can lead to a wine with fewer vegetal aromas.

But if the leaves are removed after véraison, it could be too late. Light exposure post-véraison has been shown to have little effect on IBMP levels.

So in other words, berries that get more sunlight early on in the summer typically have less IBMP. This can explain why wines from cool, cloudy climates tend to have more green bell pepper aromas.

Can anything be done in the cellar to get rid of this smell?

Yes, thermovinification, or fermenting the grape juice at a really high temperature for a short period of time, can help. Since IBMP is volatilized at 50°C (122°F), quickly increasing the temperature of the wine can help to get rid of some of those vegetal aromas.

Do vegetal aromas go away with time?

Probably not. It’s been shown that for a red Cabernet Sauvignon and a white Sauvignon Blanc, after three years of aging in a dark cellar, there was no change to IBMP levels. This is why it’s so important to control in the vineyard!

To summarize:

  • Pyrazines give off vegetal aromas in wines.
  • IBMP, the most common pyrazine in wine, has a green bell pepper smell.
  • Pyrazine aromas are most common in Bordeaux varieties, like Cabernet Sauvignon, Merlot, Cabernet Franc, and Sauvignon Blanc.
  • Sunlight exposure before véraison can decrease IBMP levels in berries. This is why wines from cloudy, cool-climates tend to have more vegetal aromas.
  • Thermovinification, or quickly heating the wine to a very hot temperature, can volatilize IBMP. This reduces vegetal aromas in wine.
  • Pyrazine aromas in wine do not seem to go away after wine aging.

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