Jamie Goode: Methoxypyrazines and greenness in red wine
By Jamie Goode, 4 April 2022
Is green good? Is green good in red? Can you taste a colour? In the case of green, it seems you can, and the relative merits of green flavours in red wines in one of the interesting stylistic and winegrowing questions in the wine world.
Green is a descriptor often used in tasting notes of red wines, and commonly it’s a negative one. Some of the tasting terms that are used to describe greenness include herbal, grassy, vegetal, asparagus, green pepper, and even ‘green tannin’.
There are a number of chemicals present in wine that can contribute to these green flavours, but there is one group of compounds in particular that is strongly associated with green aromas and flavours in wine: methoxypyrazines (technically, alkylmethoxypyrazines), which were first discovered in green peppers back in 1969 and are present in green tissues of plants. The main one we are interested in, in a wine context, is isobutyl-methoxypyrazine (IBMP). Typical concentrations found in wines would be in the range of 5-30 nanograms/litre. That’s significantly above the sensory threshold in water, which is just a couple of nanograms a litre (the sensory threshold in wine, especially red wine, is higher at around 15 nanograms/litre). The other ones identified in wine are isopropyl-methoxypyrazine (IPMP) and sec-butyl-methoxypyrazine (SBMP), which are usually at much lower levels, but could still play a role contributing to these green flavours.
They are present in unripe grapes, and together with tannins, they seem to act as anti-feedants. Methoxypyrazine levels gradually increase in grapes as the berries grow, reaching a maximum just before veraison (where the berries change colour and begin to soften). Then they start to decrease in level as ripeness approaches.
Unripe grapes have high levels of methoxypyrazines, and this deters the birds from eating them – the grapevine doesn’t want them to be eaten until the seeds are developed enough to be able to germinate when deposited by the birds after eating with a dollop of fertilizer. Try an unripe grape: they are very green, very acidic, and very tannic.
As ripening approaches, the methoxypyrazine levels begin to fall, just as the sugar levels increase and the acids are metabolized. So greenness in red grapes is a sign of unripeness. A common viewpoint among viticulturists is that one way of reducing methoxypyrazine levels is to expose the grapes to the sun. So they pluck the leaves in the fruit zone, thinking that the sunlight will degrade the methoxypyrazine. But there’s very little evidence for this photodegradation actually occurring. Still, leaf removal seems to have some effect, especially when it’s done early on. This might be because of reduced accumulation rather than increased degradation. In fact, there is evidence that if the vine is growing rapidly during this period of methoxypyrazine accumulation, then more methoxypyrazine is accumulated, independent on the level of cluster shading. So for red wines you really want vine growth to slow down just before the methoxypyrazine accumulation phase. If methoxypyrazines are present in the grapes at harvest, because they are very stable compounds, they tend to persist through fermentation and then stay at the same level in the final wine. Green doesn’t go away, once it’s there.
So if ripeness is desirable in red wines, it follows that greenness – a sign of underripeness – is undesirable, right? Well, yes and no.
Green is a frequent contributor to the aroma profile of the Bordeaux grape varieties Cabernet Sauvignon, Cabernet Franc and Merlot. Carmenère, a Bordeaux variety that relocated to Chile, also has high levels of green. Good red Bordeaux, for example, often has green in its signature. In most other well-known red varieties, methoxypyrazines are below detection levels in ripe grapes. So when it comes to most red grapes, if green is detectable then the other flavours aren’t ripe and the wines that result aren’t very nice. But when it comes to these Bordeaux varieties, the grapes can be appropriately ripe and still have some greenness, and the resulting wines can be in balance, with nice ripe flavours, but still be a bit green.
One problem, though, is winemakers working with the Bordeaux red varieties and looking to eliminate all traces of green. This fight against the intrinsic nature of these varieties often ends up with jammy, over-ripe wines with elevated alcohol levels. This attitude to green isn’t unusual, and has resulted in what has been dubbed the ‘international’ style of red wine that involves very ripe grapes with high alcohol and structure provided by oak.
One reason green gets a bad rap in South African reds is that often it’s there as a result of underripeness caused by viral infection of vines. Vines with grape leafroll virus often have delayed berry maturation, and can make red wines with high levels of green in them, because they develop to a certain point and then just stick. Often, winegrowers leave the grapes on the vine in an attempt to ripen out the greenness, but it’s not as simple as this: extra hang time may not always be effective in reducing methoxypyrazine in virused vines beyond a certain point.
One other source of greenness in wine is from the use of stems in winemaking. This is an interesting topic in its own right, and deserves its own discussion, but when whole bunches are used in fermentation they can contribute green flavours to the wines.
So green is all about context, and balance. I think some winemakers are simply too scared by it and try to ripen it out, often with disastrous results: over-ripe, formless wines with a jammy character. Green done well is a perfect framing for crunchy, just-ripe fruit, which supports a graceful ageing. As an exaggerated character in a wine, it’s not desirable, and I find green plus high ripeness particularly off-putting. Aiming for homogeneous ripeness helps here, and allows grapes to be picked in that lovely place of tension where they are only just ripe, with a hint of green that acts as a foil to the fruit – especially for Bordeaux varieties.
- Jamie Goode is a London-based wine writer, lecturer, wine judge and book author. With a PhD in plant biology, he worked as a science editor, before starting wineanorak.com, one of the world’s most popular wine websites.
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