 IVES 9 IVES Conference Series 9 Inhibition of reductive characters in wine by cu-organic acids: predicting the duration of protection

Inhibition of reductive characters in wine by cu-organic acids: predicting the duration of protection

Abstract

Cu organic acid complexes efficiently bind hydrogen sulfide in wine and therefore prevent its accumulation and subsequent reductive off-flavour [1]. This fraction of Cu can also bind methanethiol, the other main contributor to reductive wine characters, albeit with less efficient binding than for hydrogen sulfide [1]. However, during bottle aging of wine, the concentration of Cu organic acid complexes gradually decline and the sulfide-bound form of Cu increases. The point at which the Cu organic acid concentration is depleted signifies a potential for reductive aroma development to occur. The aim of this study is ascertain how long Cu organic acid complexes in wine can offer a protection against the reductive aroma compounds. High (0.6 mg/L), medium (0.3 mg/L) and no (0 mg/L) Cu(II) additions were made to Pinot Grigio and Chardonnay wines at bottling, and the bottled wines were then stored at 14 °C in darkness. Analysis was performed on the wines at 0, 2, 4, 8 and 12-14 months after bottling. Throughout bottle ageing process, the concentrations of three different Cu fractions, attributed to Cu organic acid complexes, Cu thiol complexes and sulfide-bound Cu, were monitored by stripping potentiometry and colorimetric methods. The free and salt-releasable concentration of hydrogen sulfide and methanethiol were determined by gas chromatography with chemiluminescene detection. Sensorial analysis was also performed on the wines after 12 months. During the first 2-months of bottle aging of all wines, the Cu-organic acid concentrations initially remained stable or increased, as total packed oxygen was consumed. Afterwards, during the low oxygen aging phase of the wines, the Cu-organic acid concentration declined exponentially with a concomitant increase in sulfide-bound Cu. These changes in sulfide-bound Cu were matched by an increase the salt-releasable hydrogen sulfide concentrations of the wines during aging. Free concentrations of hydrogen sulfide and methanethiol were only found to accumulate in wines without any Cu-organic acid present at bottling. For the Pinot Grigio without Cu-organic acid present at bottling (i.e., the no Cu addition treatment), the free methanethiol concentrations in the wine were above the aroma threshold and this wine was assessed as reductive. Alternatively, for the Pinot Grigio with Cu-organic acid complexes at bottling, only concentrations of free methanethiol below the aroma threshold were measured and the wine was not reductive. The decay in Cu-organic acid complexes, in the low oxygen aging phase of the wines, were found to follow first order kinetics that were similar for the Chardonnay and the Pinot Grigio. These results enable determination of the time-frame that Cu-organic acids can offer white wine protection against the potential accumulation of reductive aroma compounds.

DOI:

Publication date: September 14, 2021

Issue: Macrowine 2021

Type: Article

Authors

Xinyi Zhang

National Wine and Grape Industry Centre, Charles Sturt University, Wagga Wagga, Australia,Nikolaos KONTOUDAKIS (Laboratory of Enology and Alcoholic Drinks, Department of Food Science and Human Nutrition, Agricultural University of Athens) John W. BLACKMAN (National Wine and Grape Industry Centre, Charles Sturt University) Andrew C. CLARK (National Wine and Grape Industry Centre, Charles Sturt University)

Contact the author

Keywords

cu organic acid complexes, hydrogen sulfide accumulation, white wine bottle ageing

Citation

Postveraison shoot trimming in Tannat and Merlot: preliminary results on yield components, plant balance and berry composition

There is currently a trend towards the production of wines with low alcohol content. To achieve this, grapes with low sugar content must be used. There are techniques at the vineyard level that can delay ripening and avoid excessive sugar accumulation without, a priori, affecting the final polyphenol content. Postveraison shoot trimming (PVST) is experimentally evaluated for these purposes, but its impact under Uruguayan climatic conditions with high interannual variability is not known. The aim of this work is to assess the PVST in Tannat and Merlot cultivars and their impact on yield components, plant balance and berry primary composition. In this study, two commercial vineyards of 10 years old Tannat and Merlot (grafted on SO4) at Canelones Department were selected. During the 2020-201 growing season, grapevines were submitted to PVST when grapes reached 15º Brix. In a randomized block, trimmed (T) and control (C) plants were evaluated with three repetitions each cultivar. Evaluation of the evolution of primary berry composition during ripening, measurement of yield components and plant balance were performed. For both cultivars, PVST did not affect yield components. Merlot reached 5.4 kg per plant and Tannat 7.1 kg, with not statistical significance between treatments. However, statistical differences were observed in terms of plant balance. In Merlot Ravaz Index reached a difference of 5.3 (12.0 in T and 6.7 in C) meanwhile Tannat reached 3.5 of statistical difference (13.7 in T and 10.2 in C). The tendency to imbalance for the treated plants had an impact on the final grape composition. Merlot grapes showed statistical difference in final total acidity (0.3 g of difference between treatments) while treatments impact final sugar content on Tannat grapes (10.0 g of difference between treatments). Further studies are needed to assess the impact of different canopy management techniques in our conditions.

Mapping and tracking canopy size with VitiCanopy

Understanding vineyard variability to target management strategies, apply inputs efficiently and deliver consistent grape quality to the winery is essential. However, despite inherent vineyard variability, the majority are managed as if they are uniform. VitiCanopy is a simple, grower-friendly tool for precision/digital viticulture that allows users to collect and interpret objective spatial information about vineyard performance. After four years of field and market research, an upgraded VitiCanopy has been created to achieve a more streamlined, technology-assisted vine monitoring tool that provides users with a set of superior new features, which could significantly improve the way users monitor their grapevines. These new features include:
• New user interface
• User authentication
• Batch analysis of multiple images
• Ease the learning curve through enhanced help features
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Use-case examples are presented to demonstrate the quantification and mapping of vineyard variability through objective canopy measurements, ground-truthing of remotely sensed measurements, monitoring of crop conditions, implementation of disease and water management decisions as well as creating a history of each site to forecast quality. This intelligent tool allows users to manage grapevines and make informed management choices to achieve the desired production targets and remain profitable.

Phenolic composition of Tempranillo Blanco grapes changes after foliar application of urea

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Leaf vine content in nutrients and trace elements in La Mancha (Spain) soils: influence of the rootstock

The use of rootstock of American origin has been the classic method of fighting against Phylloxera for more than 100 years. For this reason, it is interesting to establish if different rootstock modifies nutrient composition as well as trace elements content that could be important for determining the traceability of the vine products. A survey of four classic rootstocks (110-Richter, SO4, FERCAL and 1103-Paulsen) and four new ones (M1, M2, M3 and M4) provided by Agromillora Iberia. S.L.U., all of them grafted with the Tempranillo variety, has been carried out during 2019. The eight rootstocks were planted in pots of 500 cc, on three soils with very different characteristics from Castilla-La Mancha (Spain). In the month of July, the leaves were collected and dried in a forced air oven for seven days at 40ºC. Then, the samples were prepared for the analysis determination, carried out by X-Ray fluorescence spectrometry. The results obtained showed that in the case of content in mineral elements in leaf, separated by soil type, we can report the importance of few elements such as Si, Fe, Pb and, especially, Sr. The rootstock does not influence the composition of the vine leaf for the studied elements that are the most important in determining the geochemical footprint of the soil. The influence of the soil can be discriminated according to some elements such as Fe, Pb, Si and, especially, Sr.

Geospatial trends of bioclimatic indexes in the topographically complex region of Barolo DOCG

Barolo DOCG is an economically important wine producing region in Northwest Italy. It is a small region of approximately 70 km2 gross area. The topography is very complex with steep sloped hills ranging in elevation from below 200 m to 550 m. Barolo DOCG wine is made exclusively from the Nebbiolo grape. Bioclimatic indexes are often used in viticulture to gain a better understanding of broader climate trends which can be compared temporally and geographically. These indexes are also used for identifying potential phenological timing, growing region suitability, and potential risks associated with expected climatic changes. Understanding how topography influences bioclimatic indexes can help with understanding of mesoscale climate behaviour leading to improved decision making and risk management strategies. The average monthly maximum and minimum temperatures, the Cool Night Index, the Huglin Index, and the monthly diurnal range (from July to October) were calculated using data from 45 weather stations within a 40 km radius of the Barolo DOCG growing area between the years 1996 and 2019. Linear and multiple regression models were developed using independent variables (elevation, aspect, slope) extracted from a digital elevation model to identify significant relationships. Bioclimatic indexes were then kriged with external drift using independent variables that showed significant relationships with the bioclimatic index using a 100 m resolution grid. The maximum monthly temperatures and the Huglin Index showed consistent significant negative relationships with elevation in all years. The minimum monthly temperatures showed no relationship with elevation but in some months a small but significant relationship was observed with aspect. Due to the lack of a relationship between minimum monthly temperatures and elevation compared to the significant relationship between maximum monthly temperatures and elevation, monthly diurnal range had a negative relationship with elevation.