Noble rot on Verduzzo friulano grapes and organoleptic properties of Ramandolo wines

Apertura_portaleHistorically on the north-eastern hills of Friuli, some grape varieties (Verduzzo friulano and Friulano) were harvested late in over-ripening, after the rains of late September with a strong infection of Botrytis cinerea. This practice has been largely abandoned over the last decades and the grapes are nowadays dried in withering rooms where it is easier to maintain the relative humidity and temperature.
The development of Botrytis cinerea undergoes two different paths as related with the microclimate at fruiting zone. If the relative humidity is limited, the Botrytis evolves into noble form (Tosi et al. 2006) while, if the humidity is high, the mycelium grows and develops outside with the grey mold. In the Bordeaux region, the conditions are the best in order to obtain a controlled development of noble rot. Thus, the high relative humidity in the morning caused by the fogs favors the proliferation of Botrytis, while immediately after the moisture is removed by the winds and the fungus is forced to remain confined inside the berries.
The grapes affected by Botrytis lose water very quickly, with a significant shortened time for withering. But the most interesting advantage of noble rot is related with the changes of the aromatic properties of grapes and wine (D’Onofrio 2011; Thibon et al. 2011; Tosi et al. 2006).

How to obtain a controlled development of noble rot?

On the basis of these considerations, since 2007 a trial was set up with the aim to develop a protocol for the production of botrytised grapes in the Friuli Colli Orientali and Ramandolo Consortium. The wines obtained with the variety Verduzzo friulano actually lack of olfactory descriptors, so the development of noble rot could be a successful way to enrich the complexity of this incredible wine.
The experiments were carried out from 2007 onwards in the winegrowing area of Friuli Colli Orientali & Ramandolo D.O.C. (North-Eastern Italy). As it normally happens for pioneers, there were several issues to be examined, since even the literature did not include any clear guidance on how to obtain a controlled development of noble rot.
The first experiments date back to the season 2007, when we wanted to ascertain if the inoculum of Botrytis cinerea in the field could result in the infection of the bunch. As often happens, the first results obtained were not the ones sought, since the noble rot did not develop.
In the following year, some lots of grapes were harvested in boxes stacked on pallets and let to dry in a conditioned room. The grapes were then sprayed with different water volumes with the aim to increase the relative humidity, which was maintained high by wrapping the pallets with a transparent plastic film. After five days the plastic film was removed and the moisture removed using powerful fans. One pallet that stayed longer in the presence of moisture (8 days), was the only one that showed a very high percentage of grapes with noble rot. It was clear that the high relative humidity for a long time was the key factor for the development of noble rot.

Temperature

In the year 2009, two levels of temperature (20°C and 30°C) were tested together with different volumes of water sprayed on pallets, and the grapes were picked in two successive maturation stages. The results indicated clearly that the more ripen grapes were more susceptible to the infection of noble rot. As regard temperatures, the highest level was detrimental since was favouring the development of sour rot for the greater presence of Drosophyla melanogaster.

Cluster microclimate

During 2010, the meteorological course of the season was particularly rich in rains, and this fostered a good inoculation of Botrytis on grapes. In several vineyards sensors of temperature and relative humidity were positioned in order to evaluate the different microclimates around the clusters, with the aim to highlight the areas more favourable for a good development of noble rot (Degano et al. 2014). By examining the differences among the different vineyards, it was clear that in the plain the temperature was higher even at the end of the season, while lower in the hills. The relative humidity was surprising, with mean values in the plains, the lowest at the top high and significantly higher in the middle hill. From these first data we could guess that the development of noble rot was very different in the vineyards monitored.
The following season 2011 was particularly hot in the summer and with rare occasions of rain. In this year the differences between the vineyards monitored were even greater in terms of temperature and humidity. The vineyards of the highest hill showed higher temperatures and lower relative humidity as compared with all the other vineyards. As regard the plain and the middle/low hill the cluster microclimate was characterized by lower average temperatures and higher relative humidity.
Up to date, the data collected highlight how the relative humidity is the key factor to obtain the development of noble rot, and in rainy years most of the areas can provide a good result. On the contrary, in hot and dry years, the most interesting results are obtained in the plains, where water is more abundant, and in the vineyards in the medium-high hills especially in the case of favourable exposures, where the relative humidity is higher.

Sensory notes

The oenological trials performed with noble rot showed important results as regard the aromatic quality of the wines Ramandolo, in agreement with the findings of Fedrizzi et al. (2011) on Amarone and Tosi et al. (2006) on the production of Recioto di Soave.
While variations in colour were very limited, the organoleptic properties of the wines showed appreciable differences.
Ramandolo presents a quite limited aromatic bouquet, and noble rot was profitable to improve the sensory properties of the wine with floral (elderberry, jasmine) and fruity notes. Among the latter group, a bigger contribution of orange and cedar (citrus aroma), apricot (stone fruits), pineapple and mango (exotic fruits) aromas was ascertained.
The results obtained so far allowed us to highlight the potential of noble rot development on Verduzzo friulano, although many efforts are still needed with the aim to optimize the technique and examine the changes in the aromatic pattern in wines.

(in a box) The organoleptic analysis
The results of organoleptic analysis of Ramandolo wines produced with dried and botritized grapes in the season 2012. The degustation took place in January 2014. As it can be seen, noble rot was profitable to improve the sensory properties of the wine with floral and fruity notes.

(in a box) Literature cited

Degano F., Bigot G., Paladin M., Vizzutti S., Comelli P., Stocco M. and Sivilotti P. (2014). L’induzione della muffa nobile su Verduzzo friulano: differenze territoriali e cambiamenti nelle proprietà organolettiche dei vini Ramandolo. Enologo 50(4):86-91.
D’Onofrio C. (2011). Caratterizzazione funzionale della biosintesi degli aromi delle uve durante lo sviluppo dell’acino e controllo della qualità aromatica delle uve. Review n. 13. Italus Hortus 18(1): 39-61
Fedrizzi B., Tosi E., Simonato B., Finato F., Cipriani M., Caramia G. e Zapparoli G. (2011) Changes in wine aroma composition according to botrytized berry percentage: a preliminary study on Amarone wine. Food Technol. Biotechnol. 49(4): 529–535.
Thibon C., Dubourdieu D., Darriet P. e Tominaga T. (2009). Impact of noble rot on the aroma precursor of 3-sulfanylhexanol content in Vitis vinifera L. cv Sauvignon blanc and Semillon grape juice. Food Chem. 114(4): 1359-1364.
Tosi E., Verzillo A., Marangon A. e Zapparoli G. (2006). Ruolo di Botrytis cinerea sulla qualità del Recioto di Soave. Informatore Agrario 62(29): 52-56.

Article by Paolo Sivilotti and Francesco Degano

Submit your comment

Please enter your name

Your name is required

Please enter a valid email address

An email address is required

Please enter your message

Vineyard, Wine and Quality © 2017 All Rights Reserved