Macrowine 2021
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

Related articles…

Mapping aromatic profiles of Chardonnay and Sangiovese wines in grafting combination with new rootstocks

Rootstocks play a key role in the adaptation of grapevine to environmental conditions, affecting phenology, vigour, yield and grape quality.

EFFECT OF OXIDATION ON LOW MOLECULAR WEIGHT PHENOLIC FRACTION, SALIVARY PROTEINS PRECIPITATION AND ASTRINGENCY SUBQUALITIES OF RED WINES

Changes in the low molecular weight phenolic fraction, obtained by liquid-liquid microextraction technique, were studied after controlled oxidation of two typologies of Sangiovese wines (Brunello di Montalcino and Chianti Classico) belonging to two vintages (2017 and 2018). The fractions were characterized by LC-MS and quantified by HPLC. The most abundant extracted compounds were the phenolic acids. The effect of oxidation, vintage, and wine typology was stated by a three-ways ANOVA. Gallic and syringic acids significantly increased after oxidation while (–)-epicatechin decreased the most.

On-the-go resistivity sensors employment to support soil survey for precision viticulture

There is an increasing need in agriculture to adopt site-specific management (precision farming) because of economic and environmental pressures. Geophysical on-the-go sensors, such as the ARP (Automatic Resistivity Profiling) system, can effectively support soil survey by optimizing sampling density according to the spatial variability of apparent electrical resistivity (ER).

Aromatic maturity is a cornerstone of terroir expression in red wine

Harvesting grapes at adequate maturity is key to the production of high-quality red wines. Enologists and wine makers define several types of maturity, including technical maturity, phenolic maturity and aromatic maturity. Technical maturity and phenolic maturity are relatively well documented in the scientific literature, while articles on aromatic maturity are scarcer. This is surprising, because aromatic maturity is, without a doubt, the most important of the three in determining wine quality and typicity (including terroir expression). Optimal terroir expression can be obtained when the different types of maturity are reached at the same time, or within a short time frame. This is more likely to occur when the ripening takes place under mild temperatures, neither too cool, nor too hot. Aromatic expression in wine can be driven, from low to high maturity, by green, herbal, fresh fruit, ripe fruit, jammy fruit, candied fruit or cooked fruit aromas. Green and cooked fruit aromas are not desirable in red wines, while the levels of other aromatic compounds contribute to the typicity of the wine in relation to its origin. Wines produced in cool climates, or on cool soils in temperate climates, are likely to express herbal or fresh fruit aromas; while wines produced under warm climates, or on warm soils in temperate climates, may express ripe fruit, jammy fruit or candied fruit aromas. Growers can optimize terroir expression through their choice of grapevine variety. Early ripening varieties perform better in cool climates and late ripening varieties in warm climates. Additionally, maturity can be advanced or delayed by different canopy management practices or training systems.

Analysis of the daily minimum temperatures variability in the Casablanca Valley, Chile

The Casablanca Valley (CV) has a complex topography and is located near the Pacific Ocean. These factors generate important climatic differences in relation to other wine producing zones of Central Chile.