Shading Nets: A Current Viticultural Strategy to Mitigate the Negative Impacts of Global Warming on Grape and Wine Quality
Abstract
Viticulture is facing important challenges in cultivation and management since grapevines are particularly vulnerable to changes in environmental conditions. Heat waves, extreme temperatures, and unpredictable weather patterns have become more frequent in wine-growing regions, creating an uncertain future for growers. In response, shading nets have emerged as a promising and adaptable technology to mitigate the adverse effects of climate change on grape production and wine quality. By moderating the vine microclimate, shading nets reduce solar radiation, decrease the extreme heat and wind speed, and improve water-use efficiency, enhancing ripening dynamics and preserving berry quality. However, the effectiveness of shading nets varies depending on the shade provided and the specific characteristics of the nets, highlighting the importance of adjusting the strategies to the specific needs of each environment, productive system, and grape variety. This review explores the influence of shading nets on grapevine physiological responses, including their ability to enhance resilience to stress. It examines their impact on grape and wine quality, providing insights into this vital adaptive tool for the future of viticulture.
1. Introduction
The viticulture industry contributes to national economies and cultural heritage worldwide, and today, it is increasingly threatened by the accelerating impacts of climate change [1]. Grapevines (Vitis vinifera L.), characterized for their sensitivity to environmental conditions, are experiencing significant challenges due to the rising prevalence of extreme weather events, including heatwaves, hailstorm, spring frost, prolonged droughts, climatic anomalies, and unpredictable precipitation patterns [2, 3]. These changes have important effects on grapevine physiology, berry development, and wine quality [4]. Therefore, addressing these challenges requires innovative strategies to safeguard the future of viticulture. The rapid advance of phenological events particularly during berry ripening is one of the most critical consequences of climate change on viticulture [4]. The elevated temperatures have been shown to accelerate sugar accumulation, leading to a decoupling between sugar ripeness and phenolic and aromatic maturity [4]. Besides, high temperatures can also exacerbate oxidative stress in grapevines, impairing photosynthesis and reducing chlorophyll content, while prolonged water scarcity has been linked to declines in stomatal conductance and leaf water potential [5]. Together, these factors compromise yield and wine sensory attributes, with notable decreases in color, aroma, and acidity [4].
Shading nets have emerged as a promising adaptation strategy to mitigate the adverse effects of climate change in viticulture [6, 7]. By moderating the vine microclimate, shading nets reduce direct solar radiation and vine temperatures, creating a more balanced environment for grape development [7]. Studies have demonstrated that monofilament shading nets can lower canopy maximum temperature by 1°C–5°C, improve water-use efficiency by up to 53%, and delay the onset of severe thermal stress during critical growth stages [7, 8]. On the other hand, the black Raschell’s type nets allowed to decrease the temperature by up to 7°C with variable effects on grape quality [9]. In this respect, Palliotti et al. [10] noted that shading nets providing excessive canopy coverage could negatively impact berry quality, resulting in elevated malate levels and diminished color intensity in both grapes and wines. Our recent studies suggest that black Raschell’s nets allowed to reduce sunburn in different grapevine varieties but statistically increase cryptogamic diseases (unpublished data). Black or dense nets are highly effective in reducing temperature but may excessively reduce light levels, impairing photosynthesis and delaying ripening [9]. In contrast, photoselective nets, which filter specific wavelengths of light, could optimize light quality while providing thermal protection. However, their adoption remains limited due to cost considerations [8]. Caravia et al. [11] also demonstrated that an overhead shading net applied from veraison to harvest ameliorated the impact of heat stress through a significant reduction in berry cell death and in loss of berry mass. Thereby, the effectiveness of shading nets is highly dependent on factors such as net material, shading intensity, edaphoclimatic conditions of the vineyard, moment of net application, time of their maintenance in the canopies of the vines, net position, productive system, and grapevine variety responses [8, 12].
This review summarized the current state of knowledge on the use of shading nets to enhance grape and wine quality as an adaptation strategy in viticulture. This research aimed to provide a comprehensive understanding of how shading nets can be optimized to meet the challenges that climate change poses to the wine industry.
2. Nets Effects on Vine Microclimate and Physiological Parameters
UV polyethylene shading nets at 50% and 70% of intensity (95 g/m2 density) applied to Pinot Noir and Chardonnay for sparkling wines at veraison positively influenced grapevine physiology by reducing incident radiation [13]. These shading nets effectively reduced berry temperatures, leading to delayed ripening, preserved acidity, and lower flavonol content, key parameters for high-quality sparkling production (Table 1). Green artificial shading nets at 70% (180 g/m2) installed in the lower and middle sides of Sauvignon Blanc vines improved plant water status, obtaining higher yields, and lower sugar content of berries compared to control [16]. No significant differences were observed in stomatal conductance, CO2 assimilation rate, or transpiration among treatments [16]. This suggests that strong level of light exclusion does not significantly compromise the primary metabolism of vines. However, recent studies demonstrate that low levels of light exclusion (i.e. 15%, 26%, and 40%) could reduce sugar content (10%) and increase total acidity (10%) [21].
| Reference | Objective of the research | Nets used in the trial and moment of application | Results of the research |
|---|---|---|---|
| Basile et al. [14] | To evaluate shading net application during the preanthesis to fruit set to reduce bunch compaction without causing effects on berry juice composition in Aglianico grapevines growing under warm climate conditions. | High-density black polyethylene nets (TENAX, Viganò, Italy) to reduce ambient light in the range of 10%–90% tested. The nets were applied from preanthesis to fruit set. | Shading nets reduced the number of berries per cluster, decreasing compaction without negatively affecting berry acidity and pH. |
| Campbell et al. [15] | To evaluate the shading net effects of the characteristics of tannins in Cabernet Sauvignon grapes during the berry ripening, specifically on composition, size, and activity of proanthocyanidins. | Green-Tek type shading nets were installed since veraison at different light filtering levels (40% and 80% of shade). The shading was performed from post-veraison maturation to harvest. | Grapes with 80% shading showed a higher proportion of galloylated subunit tannins. A decrease in the molecular mass of tannins was observed in grapes without shading, resulting in lower tannin activity in fruit extracts. |
| Cataldo et al. [16] | To evaluate the impact of shade nets on Sauvignon Blanc to mitigate the effects of high temperatures and heat waves. | Green artificial UV-stabilized polyethylene shade nets at 30% and 70% of shading. Shading nets were applied at 25% veraison to harvest. | The 70% of shading reduced berry temperature and vine improved water status, increasing the accumulation of thiol aromatic precursors, such as Glu-3MH, Cys-3MH, and Cys-4MMP. This treatment delayed vine phenology compared to the control. |
| Domanda et al. [17] | To evaluate how antihail nets affect the microclimate and fruit quality of Fiano grapevines. | Crystal net (70 g/m2, shading factor of 8%) and black net (70 g/m2, 26%) installed 39 days before harvest. Nets were installed on August 2, 2023, and they were removed on September 11, 2023, after the harvest of the grapes | The nets caused a slight increase in air temperature and a decrease in relative humidity compared to the control. There were no significant differences on the content of grape parameters among the treatments and control. |
| Dufourcq et al. [18] | To investigate the partial shade nets as a strategy to mitigate the effects of climate change in vineyards in southwestern France, of Gros Manseng grape variety. | Black high-density polyethylene nets (50% and 75% of shading) were used. These nets were installed on only one side of the vine canopy (west side) to provide a partial shade from fruit set to harvest. The protective period occurred from fruit set until harvest during 76 days in 2020 and 95 days in 2021. | Shading nets reduced radiation in the canopy, especially on sunny days. Canopy temperature decreased on the hot days, with a reduction in bunch temperature of up to 4°C. This mitigation was most effective when maximum temperatures exceeded 35°C. In the moderate climatic season, a delay in grape ripening was observed, improving some aromatic compound in wines, and reducing others. |
| Martínez-Lüscher et al. [19] | To evaluate the effects of partial radiation exclusion by the use of shade nets to flavonoids and organic acids content in grapes. | Polyethylene pearl (20% of shading), aluminet (40%), blue (40%), and black (40%) nets were installed from pea size to harvest. That is, 31 days after anthesis, pepper-corn size berries, stage 29 of modified Eichhorn–Lorenz scale. | Shading nets reduced bunch temperature compared to the control, especially under the black net. The nets also altered the chemical composition of the grapes, reducing pH and increasing total acidity compared to the control. The black net resulted in a higher anthocyanin concentration toward the last weeks of grape development. |
| Ghiglieno et al. [13] | To evaluate how leaf removal and artificial shading affect the chemical composition of Pinot noir and Chardonnay grapes grown in the Franciacorta region for the production of high-quality sparkling wines. | UV-stabilized white shading nets made of polyethylene were installed from veraison (at 20%) to harvest, with a density of approximately 95 g m−2. | Artificial shading delayed grape ripening and increased its acidity, especially in treatments with a layer of mesh, improving must quality for sparkling wines. Shading nets decreased flavonol content in grapes. |
| Martínez-Lüscher et al. [20] | To evaluate the vulnerability of Cabernet Sauvignon grapes to heat waves and solar exposure and to determine whether partial shading can mitigate the negative effects of heat and solar exposure on grape composition. | Black shade netting that allowed 40% of solar radiation to pass through (60% shading) was applied on June 15, 2017, 26 days after flowering (DAF), at 100% fruit set. | Partial shading reduced cluster temperature, maintaining the content of flavonoids such as anthocyanins and flavonols. Grapes exposed to direct solar radiation suffered greater degradation of flavonoids, while shaded grapes showed less loss of these compounds, even during heat waves. |
| Lobos et al. [9] | To evaluate the effects of shading nets in a Cabernet Sauvignon vineyard and compare these effects with an untreated control in terms of vine physiology and fruit quality. | A black Raschell-type net of 35% shading was used and placed on the west side of the vine, covering the area of the clusters and a limited part of the canopy. The net was installed on December 14, 2011, and removed at harvest on April 10, 2012. | Shading nets caused a significant reduction in radiation and temperature in the fruit zone (∼7°C below the control). None of the treatments significantly affected stomatal conductance, transpiration, or CO2 assimilation. Fruit dehydration was significantly lower netting treatments compared to the control. |
| Miccichè et al. [21] | To evaluate how artificial shading impacts vegetative growth and ripening processes of the Nero d’Avola, particularly during the berry ripening and to provide alternatives to climatic challenges such as increased temperature and radiation. | Green nets with a 27% of shade factor and white nets with a 32% shade factor were used and installed from pea size to harvest. | Shading treatments significantly decreased berry weight, acidity, and pH of grapes and the white net showed a greater impact on reducing solar radiation and decreasing berry weight, while the green one increased acidity compared to the control. Both shading treatments delayed grape ripening. |
| Tosin et al. [22] | To model leaf pigments and reactive oxygen species (ROS) using hyperspectral data and to develop a virtual phenotype and validate behaviors in the photorespiration pathway under shaded and unshaded conditions. | The study used shading nets installed above and to the sides of the vine rows to modify the microclimate and reduce exposure to direct light. The study was performed during post-veraison stage. | Shaded vines presented higher chlorophyll levels, suggesting compensation for reduced available light. Nonshaded vines showed higher levels of ROS (52.10% higher), indicating higher oxidative stress. |
| Li et al. [23] | To improve grape and wine quality in a warm viticulture region by using photoselective nets in Cabernet Sauvignon to regulate metabolite accumulation, aromatic profiles, and wine sensory characteristics. | Pearl, red, and black photoselective nets, with a shading rate of 50% were installed from veraison to harvest. | Photoselective nets improved microclimatic conditions, reducing temperature, and increasing relative humidity within the canopy. The red and pearl nets increased tannins, flavonoids, and aromatic volatiles in the wine. The red net showed the best performance in improving sensory characteristics of wines, while the black net had a less favorable impact on these parameters. |
| Ju et al. [24] | To analyze the impact of light-selective shade nets on grape and wine quality of Cabernet Sauvignon, in terms of phenolic compound and aroma accumulation, in a context of high solar radiation in the Ningxia wine region of China. | Light-selective shade nets black, red, and white were used. Shading treatment was applied 2 weeks after flowering. | Solar radiation was significantly reduced by shade nets, especially the black one. Grapes grown under the black and red nets showed an increase in flavanols, while flavonoid and anthocyanin levels decreased. Black nets were the most effective in increasing the variety and content of fruity, floral, and sweet aromas in wines, while white nets reduced green and citrus aromas. |
| Lu et al. [25] | To evaluate the impact of partial canopy shading (using black shade cloth) from the pea-size stage to harvest on vine physiology, berry development, and wine composition under a semiarid continental climate | A black cloth (0.1 mm thick, 1.2 m wide, 75% absorption; Meshel Netting Co., Ltd, China) made of polyethylene was applied from the pea-size stage to harvest partially in one side of the canopy. | Partial canopy shading reduced solar radiation in the fruit zone by 74.6% compared to the unshaded control. Shading increased berry anthocyanin concentration by 11.1% (from 393.5 to 437.1 mg/L), while significantly decreasing flavonols by 52.5% (from 19.8 to 9.4 mg/L) and flavan-3-ols by 49.0% (from 91.4 to 46.6 mg/L). The resulted wines showed slightly lower alcohol content (11.9% vs. 12.3%) and exhibited higher concentrations of esters and β-damascenone. |
In warm climates, black high-density polyethylene (HDPE) shading nets that covered the whole vine at 10%, 30%, 50%, 75%, and 90% of reduction of ambient light installed between preanthesis and fruit set reduced photosynthesis linearly from 20.3 μmol m2/s to 5.3 μmol m2/s [14]. These authors reported that individual berry weight was not altered, but yield was reduced due to fewer berries per cluster [14]. In addition, phenological phases were delayed in Nero d’Avola vines when green (shade factor 27%) and white (shade factor 32%) shading nets were installed at the fruit set (BBCH 71) [21]. The results also showed a higher chlorophyll content in the shaded leaf vines, suggesting that a prolonged exposure of photosynthetic organs of green plants to high levels of light radiation may result in photoinhibition [21]. These authors noted that the shading treatment delays leaf fall, which could affect the starch accumulation on perennial reserve organs to be exploited at the following season’s budburst [21].
High-tenacity polyethylene crystal antihail nets (70 g/m2, shading factor 8%) and black antihail net (70 g/m2, shading factor 26%) installed over Fiano vines in a temperate climate scarcely affected air temperature (about 0.3°C and 0.1°C higher with black and crystal nets, respectively) and relative humidity (close 1% lower with both black and crystal nets) in the cluster zone compared to control [17]. The black net slightly increased air temperature compared to the control (27.2°C–26.9°C), while the crystal net had almost no effect (27.0°C–26.9°C). In addition, relative humidity remained nearly unchanged across all treatments, with mean values of 57%. These results suggest that antihail nets can be implemented without significantly altering the vineyard microclimate, making them a viable option for grape protection without major climatic disruptions compared to shading nets [17].
Shading nets can significantly reduce radiation on hot days, lowering canopy and bunch temperatures [9]. Under 90% shading, vine temperatures decreased by up to 4°C compared to unshaded treatments, a crucial benefit when daily temperatures exceed 35°C [8, 14, 18]. However, on cool days (< 25°C), the temperature in the canopy of Gros Manseng after applying 50% and 70% of shading nets was higher compared to a control treatment [18]. This dual effect is consistent with findings reported in Mediterranean viticultural environments [17, 26], where the application of moderate shading effectively reduced incident radiation and canopy temperature under high thermal conditions, while slightly increasing canopy temperature during cooler periods. This latter response is possibly attributable to the insulating properties of the nets and microclimatic alterations within the canopy, including reduced convective heat loss and modified airflow dynamics based on the physical properties of nets. Thus, shading nets can serve as a buffer against thermal extremes, offering both cooling during heatwaves and thermal retention in milder conditions.
The radiation intensity is significantly reduced under the black nets although the spectral components of the black and white shading nets are similar to the radiation measured in the open field. Color light-selective sunshade net significantly decreased the intensity of UV-A and UV-B radiation in Cabernet Sauvignon vines growing in the Ningxia Hui Autonomous Region, making the white net the most effective treatment [24]. In this study, a decrease of up to 88% of the incident light was observed, which helped to prevent overheating of the berries [24]. Shading nets filtered the intensity of radiation received by the vines, which was associated with a reduction in the rate of transpiration and water absorption, maintaining an optimal water balance of the vines and reducing heat stress [22].
Among the effects of shading nets on canopy physiology, the reduction in radiation reaching leaves and clusters helps to reduce canopy temperature during the hours of highest thermal stress, which contributes to lower water loss through transpiration, maintaining leaf photosynthetic activity and improving water-use efficiency. However, this effect depends on the climatic context, as addressed above [8, 9]. The results and effects of nets in the vineyards are directly affected by climatic conditions, which could be applied in specific environmental conditions. Biochemical analyses and hyperspectral data were integrated to explore adaptations of vines to shading nets, revealing higher chlorophyll levels (+117.4%), whereas the levels of reactive oxygen species (ROS) (+52.1%) increased in unshaded vines compared to the shaded ones [22]. This is especially relevant in regions characterized by hot temperatures, where the ability of vines to continue performing photosynthesis efficiently may be compromised [24]. Shading net treatments in hot and dry viticultural regions have significantly improved water-use efficiency by reducing thermal stress [8, 16].
3. Nets Effects on Grape and Wine Physicochemical Parameters
3.1. Technological Maturity
Temperature disrupts the synchronization of sugar and organic acid metabolism during grapevine ripening and induces significant transcriptome remodeling [4, 27, 28]. The pearl, red, and black photoselective nets led to grapes increasing the levels of titratable acidity and decreasing the total soluble solids and pH compared to the grapes at open field, suggesting a potential to reduce rapid sugar accumulation and delay grape ripening [23]. Total soluble solids decreased significantly by the use of light-selective nets, suggesting that these treatments might result in a decrease in carbon assimilation of leaves [15, 23]. Temperatures play an important role in berry sugar accumulation, and the optimum temperature range for the photosynthesis of grape leaves is between 25°C and 35°C [4]. These reports showed that total acidity is higher than nonshaded grapes, contributing to decreased pH, an effect to consider in warm viticultural zones. In this fashion, organic acids are key determinants of wine pH, influencing its appearance, microbial stability, and chemical balance [29]. They directly affect taste by contributing to sourness and play a critical role in moderating sweetness, creating a more balanced flavor profile in wines [29]. These changes caused by shading nets were also maintained in the produced wines, indicating that the use of this technology can reduce the sugar content and increase the acidity of grapes and wines [24]. Also, shading nets significantly decreased grape reducing sugar content from 203.50 to 177.57 g/L, limiting the availability of sugars needed for berry development and ripening [24, 30]. The lower sugar level affected the alcoholic potential of the wine, which could be an important consideration in hot and dry viticultural zones [24]. In hot climates, where rapid ripening can lead to acidity loss and excessive sugar accumulation in grapes, white polypropylene sheeting painted black on the inside effectively delays vine ripening, offering a potential advantage for producing balanced wines [30]. Berries shaded by the use of this white polypropylene sheeting showed higher levels of titratable acids, suggesting that artificial shading affects organic acid metabolism, limiting the malic acid degradation during ripening [30]. Malic acid accumulation in grapes predominantly occurs before veraison, under optimal temperatures ranging between 20°C and 25°C [4, 28]. The exposure to high temperatures, particularly above 35°C–38°C, during this stage can markedly suppress malic acid biosynthesis [28]. After veraison, the main respiratory substrate shifts from glucose to malate, which is gradually depleted through respiration, especially under elevated temperature regimes typical of warm climates [28]. The application of photoselective shading nets, particularly when implemented from fruit set to veraison, has been shown to moderate berry temperature and delay the degradation of organic acids (Table 1). Based on this, moderate to high shading intensities (30%–50%) during pre-veraison stages can mitigate thermal stress, supporting higher malic acid accumulation, while also reducing its degradation post-veraison by lowering canopy and berry temperatures [26]. This is particularly relevant in warm regions where accelerated ripening is associated with a rapid decline in acidity, often resulting in grapes with suboptimal technological maturity [4, 31]. The relative increase in acidity from photoselective nets may be positive in warm regions where fast ripening often results in grape and wine acidity loss [30]. Therefore, the relative increase in acidity observed under photoselective or shading nets may be attributed not only to reduced temperature but also to the precise timing and intensity of shade application across key phenological stages. Despite these benefits, excessive shading may inadvertently generate microclimatic conditions favorable to the development of cryptogamic diseases such as Botrytis cinerea and Plasmopara viticola, primarily due to increased canopy humidity and reduced air circulation [26]. Consequently, the intensity and duration of shading applications should be carefully optimized to provide thermal protection while minimizing phytopathological risk.
4. Shading Net Effects on Grape and Wine Phenolic Compounds
4.1. Anthocyanins
Anthocyanins are key phenolic compounds responsible for the color of grapes and wine, which also contribute to the final product’s color stability and organoleptic profile [32]. Biosynthesis of this compound is controlled by the phenylpropanoid pathway and regulated by environmental factors, such as light and temperature [33]. Anthocyanins are synthesized in the cytoplasm and transported to the vacuoles, where they accumulate and are stored as pigmented structures known as anthocyanin vacuolar inclusions [34]. The optimal temperature range for anthocyanin accumulation in grape berries is 17°C–26°C, with cooler temperatures, especially during nighttime, significantly enhancing color development in red grape varieties [4]. Berries exposed to elevated temperatures and radiation can stimulate the synthesis of anthocyanins, flavonols, and flavanols in grapes due to the increased activity of the phenylalanine ammonia-lyase (PAL) enzyme [34]. However, when temperatures exceed 35°C, the grapevine’s respiration rate rises while photosynthesis declines, resulting in reduced sugar production and the degradation or inhibited accumulation of specific secondary metabolites, particularly anthocyanins [4, 35].
The reduction of UV-B radiation and light intensity by the use of shading nets can influence the synthesis of compounds such as anthocyanins [36]. The total anthocyanin content in grapes decreased due to their full shading using white polypropylene sheeting from 0.39 to 0.07 mg per berry [30]. The reduction of anthocyanins implied a decrease in color intensity in wine, affecting the visual perception of the final product [30]. Ju et al. [24] reported that the white photoselective shading nets increased total anthocyanins in grape skins and seeds, whereas the black ones decreased their contents compared to the control in the first study season. However, in the second study season, the red, black, and white photoselective nets generally reduced total anthocyanin content in both skins and seeds compared to the control, with the exception of the black net, which did not show this reduction [24]. The interannual climatic variability, including fluctuations in temperature, solar radiation, and humidity, can markedly influence grapevine physiological processes and the accumulation of secondary metabolites in this study. These environmental differences may modulate the efficacy of shading treatments, resulting in vintage-dependent effects on phenolic and aromatic compound profiles [24]. The levels of monoglucoside, acetylated, and coumaroylated anthocyanins were also reduced under the nets, mainly due to the degradation of the malvidin forms by the use of red, black, and gray photoselective shading nets [23]. Sun exposure influences the biosynthesis of flavonoids in grapes, precisely the proportion of dihydroxylated and trihydroxylated anthocyanins [15]. However, this decrease in anthocyanins did not significantly affect the color of the final wine, suggesting that the content remains suitable for producing young or rosé wines [23]. These results proved that overhead partial shading of vineyards could mitigate anthocyanin degradation by reducing cluster zone temperatures.
4.2. Flavonols
Grape flavonols mainly accumulate in epidermal cells of berry tissues in response to solar radiation, especially UV-B [37]. These compounds allow the most harmful part of the solar spectrum to DNA to be filtered [38] and can act as natural antioxidants, improving the longevity and quality of the wines [39]. Besides, flavonols interact with anthocyanins through copigmentation effects, intensifying the color and increasing their resistance to degradation during vinification, contributing to the wine color, freshness, and bitterness [39]. Grape flavonol concentration increases with high sunlight exposure before the veraison period, driven by the activation of MYB family transcription factor genes [40]. Light plays a key role in regulating the expression of flavonol synthase (VvFLS), a structural gene involved in flavonol biosynthesis [41]. Li et al. [23] reported that using photoselective nets reduced flavonol content by 20%–30% compared to control due to their effects on decreasing the exposure of vines to UV-B radiation. These results underscore the importance of reporting not only the intensity and spectral characteristics of shading but also the specific timing of application. Martínez-Lüscher et al. [37] proposed the flavonol profile as a fine indicator of the solar radiation intercepted and accumulated by berries and valuable to discuss the effect of solar radiation or canopy architecture on grape composition. Since flavonol accumulation is temporally sensitive, future research should clearly define shading periods relative to phenological stages to better elucidate interstudy discrepancies and optimize vineyard management practices. Including individual flavonol profiling could further refine our understanding of the effects of spectral light quality on berry skin composition.
4.3. Flavanols
Grape flavanols, commonly called tannins, are phenolic compounds responsible for astringency and bitterness of grapes and wines [42]. These compounds are present in the skin, seeds, and pulp and are essential for wine structure and stability [42]. The biosynthesis of seed flavanols begins after fruit set and peaks around veraison, whereas skin flavanols exhibit high levels during flowering and continue to accumulate from fruit set through to one or two weeks post-veraison [43]. Berries exposed to sunlight can enhance flavanol accumulation in grape skins and promote the formation of longer polymeric flavanols [43]. Additionally, flavanol biosynthesis in grapes may increase with rising temperatures [28, 43]. However, in warm viticultural regions, the increasingly hot conditions during berry ripening shorten the period between veraison and harvest, reducing the time for flavanol biosynthesis [4, 28].
Black and red shading nets installed over grapevines from veraison to harvest increased grape flavanol content by 106.9% compared to the control, which was crucial for improving organoleptic quality and color stability of wines, especially in warm viticultural regions [23]. In this study, the total content of flavanols, particularly catechin and epicatechin, was improved by using these aforementioned photoselective shading nets [23]. Shading nets can also affect the proportion of flavanols biosynthesized in grapes, which may directly influence the structure and quality of the wine produced. Ju et al. [24] reported that the use of photoselective nets increased the contents of total phenols, tannins, and flavanols in grapes, while the total flavonoids and anthocyanins were decreased. These authors reported that total flavanols in grape seeds and skins increased with red and black shading nets compared to open field treatments in two consecutive seasons [24]. The differences in grapes were kept in wines, suggesting that shading nets allow to contribute to the production of balanced wines in terms of quality and color [24]. On the contrary, when total shading is applied to the grapes using white polypropylene sheeting painted black on the inside, flavanol content decreases, which could result in wines with less body and complexity [30].
The report published by Campbell et al. [15] evaluated the effects of artificial shading (40% and 80% of shading) applied during the ripening of Cabernet Sauvignon grapes on the composition and activity of flavanols in berry skins. The authors observed that grapes subjected to shading presented a significantly higher proportion of galloylated subunits than grapes exposed to the sun [15]. The average molecular weight of flavanols was higher in grapes subjected to 80% of shading, suggesting the impact of shading nets on tannin structure due to light reduction [15]. Martínez-Lüscher et al. [19] reported that proanthocyanidin chain length was not affected by the use of pearl (20% of shading), aluminet (40%), blue (40%), and black (40%) nets and minor changes were observed in the proportion of terminal catechin/epicatechin and seed galloylation in response to treatments. Galloylated subunits are a component of proanthocyanidins or condensed tannins found in grape skins, seeds, and stems that contribute to the structure, size, and complexity of tannins, affecting wine’s astringency [42]. Galloylation increases the polarity of tannins, influencing their interaction with salivary proteins, thus enhancing the perception of astringency [42]. In addition, the flavanol activity was lower in sun-exposed fruit than in the shaded ones [15]. Galloylated subunits possess strong antioxidant activity, which helps protect wine from oxidative degradation [44]. This implies that larger tannins composed of galloylated subunits in shaded grapes could also contribute to beneficial properties and astringency of wines, affecting the interaction of tannins with salivary proteins. Based on these results, shading nets can modulate the sensory characteristics of wines, particularly color, bitterness, and astringency. Furthermore, tannin activity can serve as an indicator to predict these characteristics and help winemakers adjust their practices to achieve specific wine styles [15].
4.4. Aromatic Compounds
Volatile compounds in grapes are critical components of varietal aroma that define the flavor profile of the wine, contributing significantly to its sensory characteristics [45]. Volatile compounds are secondary metabolites with protective functions against biotic and abiotic stress [46]. High temperatures and excessive solar radiation can alter aromatic precursors; for example, terpenes (such as linalool and geraniol) and norisoprenoids (such as ß-damascenone) can be degraded under extreme heat conditions [47], which is why the shading nets could influence their content in grapes and wines. The content of thiols (from 4.5 nmol/L in control to 4.0 and 3.4 nmol/L for 75% and 50% of shading) and ß-damascenone (from 35.3 nmol/L in control to 27.0 and 30.7 nmol/L for 75% and 50% of shading) in wines from grapes subjected to shading nets during 95 days from fruit set to harvest was lower than the wines from grapes exposed directly to the sun in Gros Manseng [18]. This is probably due to the protection that shading nets confers to vines against oxidative stress and reduced biosynthesis of varietal compounds in grapes [18]. Despite this, in the season in which the shading nets were installed for the shortest time, there was no statistical difference in the content of volatile compounds in the wine between treatments [18]. Moreover, entire shading clusters using light shielding boxes from veraison to harvest in Cabernet Sauvignon grapevines increased the contents of β-damascenone, terpineol, 2-ethyl-1-hexanol, and 2-hexenal in grape berries [30]. The VvCCD1 genes are involved in the formation of carotenoid dioxygenases (CCD), which are key enzymes responsible for the specific oxidative degradation of a wide range of carotenoids, enabling the production of C13 norisoprenoids, including ß-damascenone in grapes [48]. High temperatures, particularly above 30°C, have been shown to promote post-veraison carotenoid degradation [49]. Furthermore, cold (20°C) and heat temperatures (38°C) have increased the expression of CCD genes, highlighting the role of environmental conditions in regulating carotenoid and C13 norisoprenoid metabolism [50].
The report published by Dufourcq et al. [18] reported that the concentration of esters was higher in wines produced from grapes growing under 75% and 50% of shading nets for 95 days compared to wines obtained from grapes exposed directly to the sun (from 30.5 μmol/L in control to 34.7 and 34.9 μmol/L in 75% and 50% of shading, respectively). In addition, the concentration of most volatile compounds such as esters, alcohols, and fatty acids in wines produced from grapes subjected to red, white, and black shading nets was significantly higher compared to the control without netting [24]. Among the different net types, black nets consistently demonstrated the highest diversity and concentration of aroma compounds, suggesting their strong influence on enhancing aromatic complexity [24]. Both red and black nets significantly improved the grapes’ fruity, floral, and sweet aromatic profiles, contributing to a more desirable sensory character in wines [24]. Conversely, white nets were observed to suppress green and citrus-like aromas, potentially resulting in a softer and less herbaceous aromatic profile. These findings highlighted the ability of photoselective nets to modulate volatile composition, adapting the aroma profiles based on the spectral modifications provided by each net type (Table 1 and Figures 1 and 2).
5. Technical Guidelines and Future Perspectives
By selectively modulating light and temperature, shading nets enable producers to face the challenges of climate change on vine production, while optimizing grape and wine quality. The effectiveness of photoselective nets on grape and wine quality under the context of global warming depends on several factors, such as characteristics of shading nets (material and color), density and shading percentage (net size, weaving system, hole shape, and weight and diameter of yarn), climatic condition (cool, intermediate, warm or hot viticultural zone), grape variety (red or white, among other differences), timing and duration of net application (growth stage and duration of coverage), installation method (covering in whole vine, in the fruit or leaf zone or partially), productive system (vertical shoot position system, open gable, or others), light quality and radiation filtering (spectral composition, light density, and diffusion), and target wine style (white, red, or sparkling wines). Future research should focus on refining the application of shading nets to enhance further their benefits on grapevine physiology and grape and wine quality. Research into the effects on specific metabolites such as amino acids, phenolic, and volatile compounds across different seasons and viticultural regions would provide more profound insights because it is a new viticultural tool for wine production. In addition, exploring cost-effective solutions for the broader adoption of photoselective nets could revolutionize sustainable practices in viticulture. Photoselective nets present a transformative approach to adapt viticulture under the context of global warming, ensuring the production of high-quality wines while safeguarding the industry’s resilience against environmental uncertainties. Shading nets, combined with viticultural practices such as irrigation, leaf removal, and cluster thinning, can help to mitigate the impacts of global warming on viticulture by improving canopy microclimate and reducing heat stress. Shading nets optimize water use by reducing evapotranspiration, protect berries from sunburn following leaf removal, and can improve fruit quality when used in combination with cluster thinning. Cluster thinning reduces vine water demand [51], while shading nets lower evapotranspiration and leaf temperature [11]. This allows the vine to allocate more resources (e.g., sugars, phenolic precursors, and amino acids) to the remaining fruit, enhancing berry composition and ripening [52]. These integrated strategies promote sustainable vineyard management under changing climate conditions. However, aspects of the useful life of the materials used in shading nets, which are mainly plastic, must be considered. Thus, the widespread use of this technology must be associated with the management of the waste generated, allowing for its collection and subsequent recycling.
Beyond their proven agronomic and enological benefits, the widespread use of shading and photoselective nets in viticulture necessitates a critical evaluation of their environmental footprint. Most shading nets are composed of HDPE, a material with limited biodegradability and long environmental persistence. As such, improper disposal or accumulation of used nets can contribute to plastic pollution in agricultural landscapes. Studies emphasize that the increasing reliance on plastic-based technologies in vineyards demands integrated waste management strategies, including collection systems and recycling protocols tailored to agricultural contexts [53]. Some reports mentioned that the implementation of recycling programs in the wine sector could significantly reduce the environmental burden associated with synthetic materials, particularly when integrated with broader sustainability certifications [53, 54]. Therefore, the adoption of shading nets should be accompanied by end-of-life strategies, such as recycling, repurposing, or transitioning to biodegradable alternatives, to ensure long-term environmental sustainability in viticultural systems and to advance in the industry’s resilience and sustainability, as discussed in the sustainable development goals (SDGs) 6 and 7 of the 2030 Agenda of United Nations [55].
6. Conclusions
Shading net utilization has recently emerged in viticulture for wine production as a strategy to mitigate the impacts of climate variability on grape and wine quality. Shading nets delayed malic acid degradation by mitigating extreme temperatures, preserving acidity levels crucial for maintaining wine freshness and balance. Photoselective nets, mainly red and black ones, effectively reduced the excessive degradation of anthocyanins in red grape varieties during heatwaves, whereas white nets decreased their contents, possibly due to excessive light reduction that could be disadvantageous under extremely hot conditions. Black and pearl nets selectively filtered UV radiation, reducing flavonol degradation under high radiation conditions while extending their biosynthesis period during cooler seasons. Red and black nets substantially increased flavanol content, particularly catechins and epicatechins, which are critical for tannin structure, wine astringency, and oxidative stability. Red and black nets significantly enhanced fruity, floral, and sweet aromas by preserving key volatile compounds such as esters and terpenes. Conversely, white nets reduced green and citrusy notes, creating a softer sensory profile.
Recent published literature shows that in both warm and cool conditions, moderate shading can modulate canopy temperature by reducing excess heat during hot periods and slightly increasing temperature during cooler days. This effect could be attributed to the insulating properties of the nets and their influence on canopy airflow and convective heat loss. Thus, shading nets may act as a microclimatic buffer, offering thermal protection across a range of environmental conditions. Based on this, the effectiveness of shading nets on grape and wine quality depends on several interacting factors, including the intensity and spectral selectivity of the net, the timing and duration of application relative to phenological stages, and the prevailing climatic conditions during the growing season. Additionally, the physiological response of the vine, the variety-specific sensitivity to light and temperature, and the microclimatic alterations induced by nets, such as humidity and airflow, further modulate its impact on primary and secondary metabolite accumulation, including anthocyanins, flavonols, and organic acids. Therefore, the successful implementation of this strategy requires careful calibration to the individual vineyard’s environmental context and production goals, balancing benefits in fruit composition with potential risks such as increased disease pressure or reduced solar-driven metabolite synthesis.
Conflicts of Interest
The authors declare no conflicts of interest.
Funding
This study was funded by FONDECYT No 11240152.
Acknowledgments
The authors would like to acknowledge the support of FONDECYT No 11240152.
Open Research
Data Availability Statement
The data or information that supports the findings of this study are available upon request from the authors.
