Effects of Climate Change in Oenology

In recent years, there have been increasing requests from wine producers, and especially from oenologists, for mitigation strategies that can reduce the effects of climate change on grape quality from an oxidative and stability of redox potential perspective, which significantly affects the shelf life of finished products.

Climate change is having a significant impact on the oxidability and redox potential of musts and wines. Here are some of the main effects observed and their implications on grape composition.

Increased temperatures and changes in rainfall patterns:

Accelerated ripening and altered pH: Higher temperatures accelerate grape ripening, leading to decreased acidity and increased pH. This makes wines more susceptible to oxidation and less stable from a redox point of view. In addition, higher temperatures can accelerate grape ripening, reducing the time available for the development of antioxidant compounds such as polyphenols.

Altered production of phenolic compounds:
Heat can affect the synthesis of phenolic compounds, important natural antioxidants in wine. Lowering their concentration or altering their composition can increase wine’s vulnerability to oxidation.

Water stress: High temperatures are often accompanied by periods of drought, which cause water stress in the vines. This can lead to overripe grapes and increased sugar concentration, further contributing to redox instability.

Aromatic precursors: Climate change can change the production of aromatic precursors in grapes, affecting the development of aromas in wine. This can lead to wines with less complex aroma profiles and worsened redox potential compared to past values on the same wine.

Dilution of phenolic compounds: Heavy rainfall, especially near harvest, can dilute phenolic compounds in grapes, further reducing the antioxidant capacity of the wine.

Increased risk of fungal diseases: High humidity promotes the development of fungal diseases, which can damage the grapes and change the composition of the wine, making it more susceptible to oxidation.

This has important implications for wine production, especially for the need to adapt winemaking practices, for example:

Early harvest: To preserve acidity and prevent overripening.
Water stress management: Through irrigation techniques and soil management.

Grape protection: Through appropriate treatments against fungal diseases.

Use of antioxidants: Such as sulfur dioxide and especially tannins, chitosan, yeast extracts rich in antioxidants such as GSH.

Winemaking techniques: That favor the extraction and stabilization of phenolic compounds, etc. Winemakers need to adapt winemaking techniques to preserve the redox potential of wines, such as using antioxidants, carefully managing oxygen, and optimizing fermentation and aging conditions.

Oxygen management: High temperatures during fermentation can promote oxidation. It is critical to carefully manage oxygen exposure throughout the winemaking process.

Choice of yeast: Some yeast strains are more resistant to oxidative stress and can help produce more stable wines.

These issues are topical to the world of scientific research, which is playing a crucial role in better understanding the impact of climate change on wine and developing adaptation strategies. This includes:

Study of oxidation mechanisms: To identify the key compounds involved and their interactions.

Development of new tools: To monitor and control redox potential and oxidative parameters during winemaking.

Experimentation of new cultural practices: To mitigate the effects of environmental stress.

Development of new grape varieties: More resistant to heat and water stress.
Development of adjuvants that contribute to oxidative protection, know how to be sacrificial and supportive elements of grape quality.

For all these reasons, climate change is a major challenge for the wine sector, but it also offers an opportunity to innovate and develop wines that are more resilient and adapted to new environmental conditions.

Adaptation strategies must start, certainly, with good vineyard management with practices such as shading, irrigation and soil management that can help mitigate the effects of water and heat stress on vines, but at the moment the results obtained are not sufficient.

The grapes arrive directly to the winery, the most critical stage in obtaining quality wines, with all the defects listed before more or less evident. Here winemaking practices, with techniques such as cold prefermentative maceration, low-temperature fermentation and aging in oak barrels can help protect the wines from oxidation. In parallel, the use of adjuvants aimed at this purpose can prove decisive in obtaining quality wines.

Likewise on wine, especially on white and rosé wines, it is crucial to protect at different stages:

Crushing phase
End of fermentation
Racking
Transfers
Storage

it is for these phases that Natural Control Redox is designed precisely to preserve the wine at each critical stage.

Susceptibility to browning in white wine

The tendency of white wine to brown is a significant concern for oenologists as it can have a negative impact on the color, aroma and overall quality of the wine. This phenomenon is mainly caused by oxidation of phenolic compounds, particularly catechins and other flavanols, which are abundant in white wine. Several factors contribute to the susceptibility of white wine to browning1,2,3,4,5

Polyphenol composition: wines with higher concentrations of phenolic compounds, particularly catechins, are more prone to browning.

Oxygen exposure: oxygen acts as a catalyst for oxidation reactions, accelerating browning.
pH: higher pH levels can increase the rate of browning.

Storage conditions: high temperatures and exposure to light can exacerbate browning.

Presence of metal ions: traces of metals such as iron and copper can catalyze oxidation reactions.

EVER Research and Development Response

In the research and development activities of EVER the development of adjuvants aimed at Oxidative protection and the redox potential of grapes and wine during the crucial stages of crushing, post fermentation and fining, focusing on 2 products:

Yeast by-products rich in glutathione:

Glutathione (GSH)-rich yeast derivatives play a crucial role in enology, particularly in the vinification of white and rosé wines.

GSH-rich yeast derivatives are available in different forms, such as specific inactivated yeasts, insoluble yeast fractions or autolysates.

Glutathione  

Glutathione (GSH) plays a crucial role in protecting wines from oxidation, a process that can lead to browning of color, loss of aromas and altered taste. GSH is a powerful antioxidant naturally present in grapes. Its protective action is based mainly on two mechanisms:

Reduction of o-quinones: GSH reacts with o-quinones, highly reactive compounds formed during oxidation of wine polyphenols. This reaction prevents the polymerization of o-quinones, which would otherwise lead to the formation of brown pigments and loss of fruit flavors.
Protection of varietal thiols: GSH is oxidized preferentially over varietal thiols, aromatic compounds responsible for many of the fruity and floral aromas in wine. This “sacrificial action” of GSH protects thiols from oxidation, thus preserving the wine’s flavor profile.

Antioxidant effect of glutathione:

Glutathione (GSH) is a natural tripeptide with powerful antioxidant and reducing properties. In white wine, GSH acts as a sacrificial antioxidant, reacting preferentially with oxidizing agents and preventing oxidation of phenolic compounds. This protective effect helps maintain the color and aroma of wine. Glutathione contributes to:

Aroma protection: GSH protects volatile aroma compounds (thiols) from oxidation, preserving the fruity and floral notes of wines and preventing the onset of unpleasant aromas.

Color stabilization and browning reduction: GSH prevents browning of white and rosé wines, maintaining their bright and attractive color.

Preservation of freshness: Due to its antioxidant properties, GSH helps maintain the freshness and vibrancy of wines over time.

Improved structure: Some yeast derivatives also contain polysaccharides, which can help improve the structure and mouthfeel of wines.

Increased longevity: GSH can help increase the longevity of wine by protecting it from oxidation during aging.

The literature indicates that concentrations between 50mg/l and 100mg/l of GSH are needed to give a lasting effect on oxidative and redox resistance. In addition, it is extremely important to point out that the use of pure GSH or GSH-rich derivatives gives very different results, as glutathione-rich yeast derivatives have a higher effect with a more “protective” reactivity of the state of the wine, intervening only when necessary 6,7,8,9,10,11.

Antioxidant effects of chitosan in must and wine

Chitosan, a chitin-derived polysaccharide extracted from Aspergillus Niger, has demonstrated interesting antioxidant properties in must and wine, although its application in oenology is still being researched and debated on new and multiple applications.

Mechanisms of action range from antioxidant activity mainly attributed to its ability to:

Chelate metal ions: Chitosan can bind to metal ions such as iron and copper, which are known oxidation catalysts in wine. By removing these ions from the medium, chitosan reduces free radical formation and prevents oxidation of phenolic compounds.

Inhibit enzyme activity: Chitosan can inhibit the activity of oxidative enzymes such as polyphenol oxidase, which catalyzes the oxidation of polyphenols into quinones, which are responsible for wine browning.

Therefore, the application of chitosan in must and wine leads to several benefits:

Prevention of browning: The chelating and inhibitory action of chitosan on metals and oxidative enzymes can help prevent wine browning, preserving its color.

Aroma protection: By limiting oxidation of phenolic compounds, chitosan can help protect wine aromas, particularly fruity and floral aromas.
Microbiological stabilization: Chitosan has also demonstrated antimicrobial properties, which could contribute to the microbiological stabilization of wine. 

Limitations and considerations: The dosage of chitosan must be carefully evaluated, as excess can adversely affect the acidity and sensory characteristics of wine. Chitosan can interact with other wine components, such as tannins and proteins, affecting their stability 12,13,14,15.16,17. 

Synergy of yeast derivatives and chitosan in wine

The synergy between yeast derivatives and chitosan in wine offers interesting prospects for improving the quality and stability of the final product. This combination takes advantage of the complementary properties of both components, enhancing their positive effects.

From EVER’s own internal research, methods were developed for the analysis of active substances in yeast derivatives and in particular GSH. The results are reported below:

Figure 1. Source - internal EVER laboratories analysis of derivatives and commercially available products rich in GSH.
Figure 2. Source-Internal EVER laboratories analysis of derivatives and commercial products rich in active antioxidants.

This allowed the selection of derivatives with a high content of active substances and in particular GSH in order to fine-tune the new product that could meet the requirements of minimum dosage and oxidative efficiency.

Similarly, several chitosanes were identified that, remaining in the CODEX specification are able to maximize the chelating efficacy of the metals Copper and Iron, among those responsible for oxidation in wines and musts.

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The abatement results of Copper are maximum with Chitosan B and can be estimated as 30% reduction of the initial value. As for Iron, the reduction is always greater than 50% of the initial value.

This is the chitosan selected to maximize the oxidative protection effects of Natural Control Redox.

NATURAL CONTROL REDOX

The task of this optimized blend between Yeast Derivative rich in active substances and in particular GSH, together with CHITOSANE B is to give maximum synergy of effects to support the oenologist in oxidative protection of musts and wines, with the following objectives:

Protect aromas: Polysaccharides from yeast derivatives can bind to aromatic compounds, protecting them from oxidation and preserving the wine’s flavor profile.

Improve mouthfeel: Glucans and cell walls can help improve the structure and mouthfeel of wine, making it softer and rounder.

Prevent oxidation: Chitosan chelates metals and inhibits oxidative enzymes, protecting wine from browning and flavor loss.

Enhanced antioxidant protection: Yeast derivatives can enhance the antioxidant action of chitosan, further protecting wine from oxidation.

Improved stabilization: The combined action of yeast derivatives and chitosan can improve the proteic and microbiological stability of wine, providing greater longevity.

Sensory optimization: The combination of yeast derivatives and chitosan can help improve the structure, mouthfeel, and flavor profile of wine.

Practical applications:

This synergy is particularly interesting for the production of white and rosé wines, which are more susceptible to oxidation. The addition of yeast derivatives and chitosan during winemaking can help preserve the freshness, color and aromas of these wines.

Specifically on the Natural Control Redox developed by EVER, the following tests were conducted:

Oxidability indexes: The absorbance at 420 nm and 440 nm is an indicator of wine browning, a phenomenon related to oxidation of phenolic compounds.
POM TEST: The POM-type oxidation test is a method for assessing the susceptibility of a wine to oxidation. It is based on measuring the rate at which wine consumes oxygen under controlled conditions. A high rate of oxygen consumption indicates a greater susceptibility to oxidation, which can lead to undesirable changes in the wine’s color, aroma and flavor. Several factors can influence the POM test result, including the concentration of polyphenols, the presence of antioxidants (such as reduced glutathione or sulfur dioxide) and the amount of dissolved oxygen in the wine. If the POM test of one wine is higher than another, it means that the first wine consumes oxygen faster than the second wine. This indicates that the first wine is more susceptible to oxidation, a process that can lead to undesirable changes in the wine’s color, aroma and flavor over time.
It is important to note that a higher POM value is not necessarily an indicator of lower quality. In some wines, a certain level of oxidation may be desirable, contributing to the complexity and evolution of the flavor profile. However, excessive oxidation can lead to defects in the wine, such as browning of color and loss of fruit aromas. Therefore, interpretation of the POM test must be done in the context of the specific wine style and the producer’s goals. A producer of fresh, fruity white wine, for example, will try to keep the POM value as low as possible, while a producer of aged red wine might accept a higher POM value.

Free Sulfur: A decrease in free sulfur dioxide (SO2) in a wine may indicate that oxidative processes are occurring. Sulfur dioxide is an antioxidant and combines with oxygen and oxidized compounds, consuming itself over time. Specifically, the decrease in free sulfur dioxide can be due to:
Reaction with oxygen: SO2 reacts with dissolved oxygen in wine, forming sulfate. This reaction is more rapid in the presence of metal ions such as copper and iron, which act as catalysts.

Reaction with quinones: Quinones are highly reactive compounds formed from the oxidation of polyphenols. SO2 reacts with quinones, reducing them back to polyphenols and preventing the formation of brown pigments.
Reaction with hydrogen peroxide: SO2 reacts with hydrogen peroxide, another product of oxidation, neutralizing it.

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Wine analysis:

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As shown in the analyses, the stability of sulfur and browning indices demonstrate the ability of Natural Control Redox to stabilize the wine under these accelerated oxidative conditions.

POM TEST analyses denote a reduction in values as dosages increase at T0 and confirm a stabilizing ability of Natural Control Redox even after 48h.

Finally, CIELab analyses denote how the product even at 48h deviates modestly from T0 especially at the higher dosages of Natural Control Redox.

The same evaluations were carried out on an aromatic wine, such as Malvasia Istriana, precisely to confirm what the literature reports on the ability of both glutathione-rich derivatives and chitosan to oxidatively protect the aromatic fractions of the wine.

Long-term evaluations on these parameters are still in progress, but in the meantime, the air-accelerated oxidative tests are reported.

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The results observed on the Malvasia are also confirmed on the Pecorino, but more importantly we see how the POM TEST manages to maintain lower values than those on the control throughout the measurement period.

Musts:

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Regarding musts, 2 musts were examined: a Chardonnay and a Pinot blanc frozen at the harvest stage from must that had been subject to flotation with about 100mg/l SO2 added.

In this case the only significant parameters we can observe are the browning indices, free sulfur and CIELab indices.

Again, the products were added increasing amounts of Natural Control Redox from 10 to 30g/hl and analyzed at T0, after 24h and 48h of exposure to air.

The indices at 420nm show a reduction as the dosage ovNatural Control Redox, increases, which is also maintained on the 24- and 48-hour measurements.

The same can be said of the free sulfur content, which drops most noticeably on the control going from T0 to 48 hours, while remaining nearly stable on the higher dosage.

CIELab indices denote changes on TQs as time passes, indices that decrease and remain more stable going instead to higher dosages and the passing of time.

Another important factor to consider is the organoleptic effect after the addition of Natural Control Redox, evidenced both by the company panel and at different events organized to taste different wines added of different dosages of the product. In all cases it is confirmed that, of course, the dosage must be proportional to the oxidative state of the wine under examination and can range from a few grams to the 30g highlighted in the trial and in all cases tasted, Natural Control Redox, brings cleanliness to both smell and taste.

Conclusions

From these findings, it can be concluded that Natural Control Redox can be a valuable support to the oxido-reductive stability of wine, ensuring sulfur preservation. It can assist aromatic protection by preserving aromas and consequently ensure better stability and organoleptic balance in all the most delicate stages of product processing and storage. 

For more information write to info@ever.it

Bibliographical references

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Climate change associated effects on grape and wine quality and production – Ramón Mira de Orduña – Food Research International Volume 43, Issue 7, August 2010, Pages 1844-1855
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Oxidation of Wine Phenolics: A Critical Evaluation and Hypotheses – Andrew L. Waterhouse, V. Felipe Laurie – Am J Enol Vitic. 2006 57:306-313
The Impact of Climate Change on Viticulture and Wine Quality – Cornelis van Leeuwen and Philippe Darriet – Published online by Cambridge University Press:  14 June 2016
Effect of glutathione and ascorbic acid addition on CIElab chromatic charateristics of Muscat Ottonel wines – Arina Oana Antoce, Gianina Antonela Badea, George Adrian Cojocaru – Agriculture and Agricultural Science Procedia Volume 10, 2016, Pages 206-214, riporta test con GSH in comparazione con Acido ascorbico con i seguenti risultati
Browning susceptibility of white wine and antioxidant effect of glutathione – Leina El Hosry, Lizette Auezova, Amer Sakr, Elie Hajj-Moussa – Food and science + Technology, 2009, conferma che la stabilità ossidativa del vino si incrementa in presenza di glutatione
Oxidation of Wine Polyphenols by Electrochemical Means in the Presence of Glutathione – Emad F. Newair, Abdulaziz Al-Anazi, and François Garcia – Antioxidants 2023, 12(10), 1891, conferma che il meccanismo di azione del GSH passa attraverso la formazione di chinoni
Effetto del glutatione e dell’anidride solforosa sull’ossidazione dei fenoli nel vino bianco – D. FRACASSETTI1, A. VANZO2, K. LISJAK2,A. TIRELLI1, W. du TOIT3 – Lavoro presentato alla 7^edizione di Enoforum, Arezzo, 3-5 maggio 2011, riporta gli effetti sinergici di GSH ed anidride solforosa
Antioxidant activity from inactivated yeast: Expanding knowledge beyond the glutathione-related oxidative stability of wine – Florian Bahuta, Rémy Romaneta, Nathalie Sieczkowskib, Philippe Schmitt-Kopplinc, Maria Nikolantonakia,⁎, Régis D. Gougeona – Food Chemistry 325 (2020) 126941, riporta in una comparazione l’efficacia dell’aggiunta diretta di GSH rispetto all’aggiunta di diversi derivati di lievito, con i seguenti risultati
Effect of SO2, glutathione and gallotannins on the shelf-life of a Cortese white wine bottled with different oxygen intakes – Silvia Motta, Antonio Tirelli, Maria Carla Cravero, Massimo Guaita, Antonella Bosso – Vol. 56 No. 4 (2022): OENO One
Efficacy of Chitosan in Inhibiting the Oxidation of (+)-Catechin in White Wine Model Solutions – Fabio Chinnici*, Nadia Natali, and Claudio Riponi – J. Agric. Food Chem. 2014, 62, 40, 9868–9875
Inhibitory effect of fungoid chitosan in the generation of aldehydes relevant to photooxidative decay in a sulphite-free white wine – Antonio Castro Marin, Pierre Stocker, Fabio Chinnici, Mathieu Cassien, Sophie Thétiot-Laurent, Nicolas Vidal, Claudio Riponi, Bertrand Robillard, Marcel Culcasi, Sylvia Pietri – Food Chemistry, Volume 350, 15 July 2021, 129222
Relevance and perspectives of the use of chitosan in winemaking: a review – Giovanni Spagna, Pier Giorgio Pifferi, Carlo Rangoni, Fulvio Mattivi, Giorgio Nicolini, Roberto Palmonari – Critical Reviews in Food Science and Nutrition, 2020
Il chitosano e le sue applicazioni in enologia – Cristóbal Lárez Velásquez, Vol. 57 No. 1 (2023): OENO One
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