Reducing quercetin levels in red wine

Q. I am looking for strategies to reduce quercetin in red wine. Does using PVPP help with this and if so, are there thoughts on how to best use it?
Gary Sheppard 
via email

A. Quercetin is one of those compounds that most winemakers never think about until it suddenly announces itself in a very visible way. It is a naturally occurring flavonol found in grape skins, part of the broader family of polyphenols that give red wines much of their structure and antioxidant capacity. In moderation, it plays a quiet, supportive role in wine chemistry, but in higher amounts it can become problematic.

The primary reason winemakers try to manage quercetin is bottle stability. Over time, quercetin glycosides extracted from the skins can slowly hydrolyze into free quercetin, which is far less soluble in wine. When enough of that free form accumulates, it can precipitate out as fine yellowish crystals or a haze in bottle. The wine itself is sound, but to a consumer it looks like something has gone wrong, and in a commercial setting this can lead to returns and lost confidence.

You may also have seen quercetin mentioned in the context of so-called “red wine headaches.” There is a recent hypothesis, still very much in the research phase, suggesting that quercetin-derived compounds could interfere with alcohol metabolism in some people, leading to higher acetaldehyde levels and headache-type symptoms. It is an intriguing idea, but it has not yet been proven in controlled human trials, so at this point it should be considered a possible mechanism rather than an established cause.

PVPP, or polyvinylpolypyrrolidone, enters the conversation because it is one of the few fining agents that selectively binds low molecular weight phenolics, including flavonols like quercetin. It is widely used in white and rosé winemaking to control browning and phenolic pickup, and in that context it is considered a fairly targeted fining. In red wines, however, it needs to be used with much more care.

The reason is simple. The same class of compounds that includes quercetin also includes many of the molecules that contribute to color, aroma, and mouthfeel. If you overdo PVPP in a red wine, you may indeed reduce quercetin, but you can also strip color, mute aromatics, and thin the palate. That is why any PVPP treatment in red wine should begin with a bench trial. On a home winemaking scale, that means taking small aliquots, say 50–100 mL, and testing a few different PVPP doses rather than treating the whole lot blindly. PVPP is typically hydrated in warm water before use, then mixed thoroughly into the wine sample. After 12 to 24 hours of contact, the wine is racked off the settled PVPP and evaluated visually as well as for taste. You are looking for the lowest dose that achieves your goal without obvious sensory damage.

Because you didn’t mention whether you are seeing quercetin precipitation, haze, or are simply trying to be proactive, I would encourage you to think about your “why” before reaching for PVPP. If you are experiencing yellowish sediment forming months after bottling, then managing quercetin precursors may be worthwhile. If not, you may be solving a problem you don’t actually have.

There are also upstream choices that influence quercetin levels. Flavonols like quercetin are strongly linked to sunlight exposure of grape skins. Highly exposed clusters tend to accumulate more flavonols than shaded ones, regardless of variety. Extraction practices in the cellar matter too. Extended skin contact, aggressive cap management, and high fermentation temperatures all favor higher flavonol extraction. 

Variety choice is less straightforward than many people assume. Pinot Noir, for example, is often thought of as “lighter” because of its lower tannin and anthocyanin content, but that does not automatically mean it is low in quercetin. Flavonols are a different phenolic family, and their accumulation is driven more by light exposure and berry physiology than by how dark or tannic the wine ends up being.

In short, PVPP can help manage quercetin, but it is a scalpel, not a sledgehammer. Use it only if you have a clear reason, always bench trial, and remember that quercetin is part of what makes red wine, well, . . . .red wine. Over-strip and you might end up with rosé!