“it’s really ugly,” says Antonino Tranchida, head oenologist at Montalcino’s Col d’Orcia. He is referring to the blue-grey flakes that look like blades of wheat floating in a wine. The residue left by quercetin allows no euphemisms, in contrast to diamond-like tartaric crystals. It’s a relatively new phenomenon – and one that consumers notice. “There are worms in my wine,” was the complaint Montepulciano-based producer Salcheto received from US clients about its 2015 Obvius.
What is it?
Quercetin is a compound belonging to the flavonoid family. It exists in many plant species. Think black tea, onions and kale as well as grapes. Like resveratrol, quercetin is believed to have important antioxidant and anti-carcinogenic health benefits. “It’s even sold on Amazon for more than €70 ($80) per 200 capsules,” exclaims Paolo Cianferoni, owner of Caparsa winery in Radda, Chianti.
Vines start synthesising quercetin at flowering and continue producing it until the end of ripening. It is the plant’s auto-defense mechanism to protect itself from ultraviolet rays. Besides being found in leaves, quercetin also builds up in the stems and skins of grapes of all colours. As it is released in the must during maceration, it is part of the phenolic composition of red wine.
Quercetin exists in two forms. As a glycoside, quercetin is soluble in water and therefore remains in suspension. Over time, quercetin decomposes, becoming a less soluble aglycone. Yet whether or not quercetin leaves a deposit appears to be a complex equation.
Quercetin accumulates in varying degrees depending on the cultivar. Sangiovese in particular demonstrates higher than average quercetin glycoside, sometimes more than 130mg per litre in fully ripened grapes. While this decreases considerably after fermentation, the amount of quercetin aglycone increases. More significantly, Sangiovese seems to be one of the few varieties susceptible to precipitation. According to Tranchida, Cabernet Sauvignon, Merlot, Syrah and Petit Verdot may have higher amounts of quercetin aglycone, but never precipitate out. “Why?” he questions. “We are trying to figure that out.”
Tranchida first encountered quercetin when he arrived at Col d’Orcia in 2009. “I noticed a light deposit after racking; but out of 100 casks maybe only in two or three,” he recalls. Fellow Montalcino producer Jan Erbach at Pian dell’Orino also became aware of the problem with the 2009 vintage in his Piandorino, a 100% Sangiovese Indicazione Geografica Tipica (IGT) wine. “It showed a green/yellow patina on the cork,” he says. Analysis confirmed it as quercetin. Subsequently, in the 2011, 2013 and 2014 vintages, both the Piandorino and Erbach’s Rosso di Montalcino threw full deposits in bottle.
Similar anecdotes point to a significant increase in quercetin deposits in Montalcino’s wines. But as the phenomenon is very recent, no hard statistics exist. The issue is echoed, albeit to a lesser extent, throughout the hills of Tuscany. As Sangiovese is Italy’s most widely planted grape and the star of renowned reds like Brunello, Chianti Classico and Vino Nobile di Montepulciano, this is a concerning trend.
The problem is neither a question of quality nor flavour. “Despite being odourless and tasteless, consider that essentially no one knows what it is,” says winemaker Michele Manelli. “It was difficult to calm the waters,” he continues, referring to the reaction to Salcheto’s 2015 Obvius. In a letter of explanation to customers, Erbach emphasised “it is indeed absolutely not dangerous for human health” – quite the opposite, given quercetin’s antioxidant properties.
However, aesthetically it presents a substantial commercial challenge. Quercetin blows tartaric crystals out of the water. It’s like shaking up a snow globe without the flakes settling. And rather than charming fluffy white crystals, it looks more like harmful needles or crawling insects.
Research is still in early stages. Col d’Orcia is collaborating with a research and analysis laboratory, the Institute for Viticultural, Oenological and Agro-industrial Development (ISVEA). Besides trying to understand exactly what quercetin is, the goal is to determine what elements in the vineyard trigger a greater or lesser amount and what happens to quercetin during maceration, alcoholic fermentation and ageing in both bottle and barriques.
The interplay between light and temperature provides a starting point. “In bunches deprived of light, there is no synthesis of quercetin,” explains Tranchida. “In partially shaded bunches, it happens slowly and in fully exposed bunches, it is accelerated.” As synthesis increases with light exposure, higher temperatures speed up the subsequent degradation, according to Tranchida. To illustrate his point, he cites 2014. It was a very rainy year requiring extensive de-leafing, exposing the grapes to ultraviolet rays. However, temperatures were not high enough to then oxidise the quercetin. The result “was a greater amount of quercetin in the vines”.
These observations don’t necessarily resonate with others. “The problems started seriously in 2003,” says Federico Cerelli, winemaker at Castello di Gabbiano. In this notoriously hot vintage, he was among those to de-leaf very early (during flowering) as a technique to build up the grape’s resistance to sunburn. However, there were consequences. “This is when we had the greatest amount of quercetin,” he says.
While producers’ individual experiences with quercetin may differ, they are united in referencing climate change as one of the crucial factors. “It has prompted an increase in ultraviolet [rays] that penetrates even in cloudy conditions,” says Cianferoni. Furthermore, managing leaf cover is an important defence. In Chianti Classico, Isole e Olena’s Paolo De Marchi reports that he has yet to have issues but was worried in 2017. “I try not to remove too many leaves and only expose the grapes to the morning and evening sun,” he says.
What’s driving it?
Given the varying manifestations of quercetin, other factors must be at play. Cerelli isn’t alone in believing that clones richer in colour and polyphenols might increase quercetin. “The clones of today have smaller berries while those of the past had more pulp, less flavonoids and more water. Therefore, older clones, even in a warmer year, would have a lower concentration of quercetin,” he says. Col d’Orcia’s tests on clones have yet to corroborate this though to date they have only evaluated two. In trials with rootstocks, however, they have found differences. Comparing 1103 Paulsen, 420A and 101-14 grown in the same vineyard using the same clone, 101-14 produced almost two times more quercetin than the former two.
Soil and elevation are still other aspects to consider. Chiara Condello, who makes wine in Emilia-Romagna, hasn’t had problems with quercetin. “But it is a different territory with lower altitudes and its own soil,” she says. Condello also works with a massal selection of old vines that have biotypes specific to her area.
Winemakers are not completely at the mercy of Mother Nature. They have the ability to analyse the quantity of quercetin in the must and wine throughout vinification. They can also determine the potential for a deposit. “For our Brunello, with 12mg per litre of quercetin aglycone we don’t have any precipitation in the bottle,” says Tranchida. When there is a chance, however, the timing of precipitation is unpredictable. If it doesn’t happen before bottling, “the risk is having the wine returned citing a defect,” says Cianferoni.
Precautionary measures are limited to refrigeration and fining agents such as potassium caseinate, carbon and polyvinylpolypirrolidone (PVPP). Usually used for white wines to correct colour, synthetic fining agent PVPP is considered the least invasive as it absorbs less perfume and structure. However, it is not typically recommended for reds because it is non-selective. “It does not resolve the problem,” says Erbach. “It just lowers unspecifically the quantity of all polyphenols in the wine.” It is also thought to flatten a wine’s flavours. Finally, as PVPP is not permitted in organic or biodynamic wines, it isn’t an option for numerous producers.
As an alternative, winemakers are adjusting vinification practices. “Modern winemaking is more reductive than in the past,” says Cerelli. Conversely, he relies on oxygen to encourage precipitation before bottling. “For some time now I have stabilised colour with oxygen, giving 1mg-2mg per litre per day after alcoholic fermentation,” he says. This, along with further micro-oxygenation before bottling, has helped resolve issues with quercetin as well. In the same vein, Col d’Orcia has increased the number of rackings to give the wine more oxygen. “At the moment, the best solution is to delay bottling,” adds Cianferoni, who waits until his Chianti Classico is in its fourth year.
However, these techniques do not provide an absolute guarantee. Through its research, which included samples from other Montalcino producers, Col d’Orcia discovered a comparatively high amount of quercetin glycoside in its wines. This can take years to transform into quercetin aglycone with that unsightly deposit occurring in the bottle. “From a reputation standpoint, we cannot take the risk of having a wine in the market with this problem,” says Tranchida. He is determined to find an enzyme which will unbind the combined form and transform it into an aglycone. “If we can liberate it immediately during maceration we could have the total precipitation of quercetin directly in the cask.”
Interestingly, issues with quercetin appear to be limited to wines made exclusively from Sangiovese. Oenologist Dr Renzo Cotarella maintains that Antinori’s only incident was in a Sangiovese from its Antica property in Napa Valley. The problem was resolved by co-vinifying it with international grapes. Dr Cotarella notes that even a minor percentage helped. “Of course, in production zones requiring the exclusive use of Sangiovese, this solution is not applicable,” he says.
Referring to the growth in wines with quercetin deposits, Manelli points out “in general, I think we are working with more 100% Sangiovese wines than in the past”. It is relatively recent that Chianti, Chianti Classico and Vino Nobile di Montalcino allow Sangiovese exclusively. And yet, Montalcino, which has always required both Brunello and its Rosso to be 100% Sangiovese, is the epicentre.
As producers continue looking for answers and solutions, they are focusing on quercetin’s favourable attributes. Besides health benefits, “it indicates the optimal ripening of the grapes and their high quality,” says Erbach. For these reasons, Manelli embraces quercetin. “I hope that we will start to speak about it in a positive way, like another beautiful wine story.”
Beauty, however, is in the eye of the beholder.