Quercetin loves Cork!

Have you found something a little strange on your SANGIOVESE wine cork?

It might be QUERCETIN…


Quercetin is a naturally occurring phenol in grape skins. It is especially high in Sangiovese, the popular Italian vine that thrives in Tuscany and other central regions, perhaps best known as the grape of Chianti and Brunello di Montalcino.

As the wine ages in the bottle, quercetin gets attracted to the cork. Often this substance looks like mould but it is actually a crystalline.

Unfortunately, “given the right circumstances it precipitates out in a yellow/green slightly gooey solid” so that can be a concern for wine drinkers who’ve not seen it before.

Quercetin can usually be removed during the clarification or filtering process, but of course this means non filtered wines (especially ‘natural’ wines) are more likely to show signs of quercetin over time.



There are an increasing number of wineries who don’t clarify their wines, or only conduct limited filtering. Why?

Well, many feel that the clarification process takes out too many of the beneficial qualities and characteristics of the wine. Or a winery focussed on natural winemaking and vegan friendly may avoid clarification*.

This makes the chance of finding quercetin on your cork more common in organic or biodynamic wineries that favour ‘non filtrato’ wine.

Eventuali depositi sono garanzia di naturale genuinità”, says one winemaker’s label (in English: “any deposits are a guarantee of natural genuineness”) which sounds rather good to me – GENUINE WINE!


* Many wineries use isinglass or casein as a fining agent (the former is made from fish bladders and the later from egg whites) so these are an issue for vegans or people with specific allergies.

The good news is that the risk to allergy sufferers seems low, given that a US study found “no detectable amount of inorganic fining agents, and only trace quantities of proteinaceous agents, are left in the wine”.

As an alternative, a type of vegetable flour can be used instead (and is becoming more popular).




The substance found on the bottom of your wine cork could actually be a cheeky bonus, because quercetin is a powerful antioxidant.

Studies have found that the “health benefits associated with consuming adequate quercetin in the diet are extensive”.

Some studies boast that “among its anti-inflammatory benefits, quercetin also helps to boost immunity, fight cancer, prevent heart disease, and improve energy levels”.

As one article says, red wine is “considered a significant dietary source of quercetin for most people”.  As a regular wine drinker, I’m glad to hear that I’m not alone if “most people” are getting their quercetin from wine too!


In summary, a bottle of Sangiovese – especially 100% Sangiovese – may have an unusual substance on the bottom of the cork, but it’s harmless and potentially good for you.

Unfortunately, quercetin can sometimes add a slightly bitter quality to the wine (because it can sometimes seep into the wine when pouring it out), so if you have concerns try decanting with a sieve/filter before serving.

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