Troubleshooting Your Wine
The faults and flaws and their analysis and resolution presented below are from my latest book, Modern Home Winemaking, where you can find additional information should you wish to explore these further.
VEGETAL CHARACTER IN CABERNET VARIETIES
DESCRIPTION
Red cabernet-related varieties — Cabernet Franc, Cabernet Sauvignon, Merlot and Carménère — as well as Malbec, have naturally occurring compounds known as methoxypyrazines, or simply pyrazines, which impart vegetative aromas of green peppers, freshly cut grass and asparagus, and are considered a flaw, particularly when excessive. Pyrazines can mask fruity aromas and become objectionable and can be very difficult to treat where they can linger for a very long time. They are easily detected given their extremely low detection thresholds in the 1–2 ng/L range, some in the pg/L range — that’s parts per trillion (ppt) and parts per quadrillion (ppq), respectively!
CAUSES
Pyrazines still present in grapes are due to underripe fruit from a wet or cold vintage or precocious harvest, or possibly from poor canopy management. The canopy of a grapevine refers to the parts of the vine visible above ground — the trunk, cordon, stems, leaves, flowers and fruit. A canopy with excessive leaves may cause too much shade therefore delay the ripening process and cause high levels of pyrazines. Pyrazines also increase if vines are allowed to carry more fruit than they can properly mature; dropping fruit just before harvest (after veraison) may be too late.
Pyrazines are found predominantly in skins, and therefore, this flaw is found mainly in red Cabernet varieties due to the maceration process.
ASSESSMENT
This flaw is easily detected by smell and assessed qualitatively; wine has an unmistakable smell of green peppers and freshly cut grass.
REMEDIAL ACTIONS
Pyrazines are very difficult to treat and their offending odors cannot always be attenuated or removed. There are, however, two solutions worth trying: treating with inactivated dry yeast or adding oak chips, or both.
Inactivated dry yeast products, such as Noblesse, have been shown, as well as in my own personal experience in dealing with an overly “green” Carménère, to be able to adsorb and reduce the offending substances.
Add Noblesse at a rate of 0.2–0.3 g/L while stirring the wine. Noblesse must be dissolved in 10 times its weight of water. Rack the wine in 3–4 days, then add more Noblesse at a rate of 0.1 g/L while stirring the wine. Once a week for the next month, stir the wine gently but thoroughly to get the sediment back into suspension to allow the inactivated dry yeast to continue its adsorbing action. After this first month, taste, smell and assess the wine. If the pyrazine odors are still present, repeat the treatment with more Noblesse at a rate of 0.05–0.1 g/L, but now, stirring the wine every second week for one month. At the end of the treatment, either after the first or second month, rack the wine and continue aging as per your program, or filter if close to bottling.
Alternatively, or if the above treatment was not sufficient, you can add oak chips to try and mask pyrazine-related odors. Here you have to use untoasted or lightly toasted oak, or a blend, and at a rate of 2–4 g/L. Taste, smell and assess the wine once a week, and remove the chips (if held in a nylon mesh bag) or rack the wine when the odors are sufficiently masked. Complete the treatment by adding finishing tannins to increase organoleptic complexities, being sure to conduct bench trials first.
If you grow your own grapes in your backyard vineyard, manage the canopy to maximize grape bunch exposure to sunlight and heat, avoiding any fruit shading, and drop fruit to balance each vine shortly after veraison. Dropping fruit is hard for home winemakers to do, leaving grapes on the ground, but it can really improve quality and uniformity at harvest.
PREVENTIVE ACTIONS
If you manage your own home vineyard, open the canopy to let the sun shine onto grape bunches to promote ripening and reduce pyrazines, particularly in a difficult vintage or in cool-climate growing areas. And don’t harvest too early, making sure to have good balance among sugar (SG/Brix), acidity, pH and phenolic ripeness.
Mitigate methoxypyrazines and their vegetal aromas by adding untoasted oak right at crush or during fermentation if you are working with a poor harvest or a variety known to have high methoxypyrazines. Untoasted oak masks the vegetal character in wines by intensifying the fruity expression and bringing forward “ripe” fruit notes without the aromas of toasted oak. And opt for a short maceration and quick fermentation to minimize extraction of methoxypyrazines.