Conversely in 2021, total free anthocyanin concentrations were the highest in D4, C0, and D1 wines. Anthocyanin modifications due to shading treatments were more varied in 2021 compared to 2020. Overall, wines from D4 had the most 3-glucosides and 3-acetylated glucosides, while C0 and D5 consistently had less. Coumarylated anthocyanin concentrations were reduced in D3 and D5 wines compared to C0 wines. This was not consistent with the concentrations observed in 2020. Likewise, there was no statistically significant effect on the anthocyanin hydroxylation ratio in 2021 wines, while shading had an impact on anthocyanin hydroxylation in wines in 2020. Nine flavonol compounds were monitored in wines using HPLC . For all monitored flavonol compounds except myricetin-3- glucuronide, C0 wines consistently had the highest concentrations in 2020 compared to shaded wines, with D4 and D5 wines following in flavonol concentration. Subsequently, C0 also had the highest wine flavonol concentration when calculated as total flavonols in 2020. A similar trend occurred in 2021. C0 wines from 2021 also contained greater concentrations of each flavonol compared to shaded treatments, as well as total flavonol concentration.The wine aroma profiles from the 2020 and 2021 vintages were analyzed with and 29 volatile compounds were identified and categorized into their respective compound classes . The aromas profiles of wines depended highly on vintage, resulting in distinct aroma profiles. Generally, in 2020, total higher alcohols were unaffected by shade treatments, except for isoamyl alcohol and benzyl alcohol. Wines produced from shaded fruit had similar concentrations of isoamyl alcohol while the C0 had the lowest isoamyl alcohol concentration. Benzyl alcohol concentrations were reduced in D3 and D5 wines compared to C0, D1 and D4 wines. In 2021, black plastic plant pots shading treatments did not impact the concentration of higher alcohols in the resulting wines except for benzyl alcohol, which increased in 2021 D3 wines compared to all other treatments.

Acetate esters and fatty acid ethyl esters showed varied effects in wines due to shading in 2020. C0 and D5 had the lowest ethyl acetate concentrations compared to the other shade treatments. Likewise, isoamyl acetate was reduced in C0, D4 and D5 wines compared to D1 and D3 wines. Among the shade film treatments , ethyl hexanoate and ethyl octanoate concentrations were comparable between D1 and D5 wines and were greater than concentrations found in D3 wines. C0 and D5 wines were indistinguishable in ethyl butyrate, ethyl-2-methylbutyrate and ethyl valerate in 2020, with D1 and D3 wines having the highest concentrations of each these ester compounds. Isobutyric acid increased in D4 in 2020. In 2021, there were no significant impacts of shading on acetate esters, fatty acid ethyl esters, ethyl butyrate, ethyl-2-methylbutyrate or ethyl valerate. The effect of shade films on various terpenes and norisoprenoids was highly dependent on vintage conditions. Alpha-terpinene was highest in D5 wines but was significantly reduced in D1 and D3 wines in 2020. The D4 wines had the most cis-rose-oxide while C0 wines had the least. Linalool concentrations were reduced in C0, D4 and D5 wines. Among the shaded treatments, nerol concentrations were enhanced in D5 wines in 2020, while there was no effect of shading on nerol concentration in 2021. D5 did not differ from the C0 in nerol concentration in 2020. Farnesol in D3 was reduced in 2020 whereas farnesol concentrations were not affected in 2021 wines. Conversely, nerolidol was unaffected by shade films in 2020, whereas significant decreases in nerolidol concentrations were observed in D4 and D5 wines in 2021. It was observed that b-damascenone were elevated in 2020 in C0 wines, yet differences in b-damascenone concentrations were nonsignificant between shade film treatments. In 2021, only significant differences in b-damascenone concentrations were observed in wines, with C0 wines containing the most bdamascenone and D5 wines containing the least. b-ionone concentrations were not statistically significant between all treatments in 2020 and 2021.

To determine the effects of partial solar shading on wine chemistry, flavonoid composition and aromatic profiles of wines we conducted a principal components analysis for both vintages . In 2020, PCA indicated that PC1 accounted for 30.8%, and PC2 accounted for 22.1% of the total variance. The C0 treatments clustered together, separately from the partial solar shading treatments. The separation along PC1 was explained by the ratio of di- to tri-hydroxylated anthocyanins in wines, norisoprenoids and flavonols, as well as lower CI, alcohol content and TPI. The separation along PC2 was explained by TA, pH, terpenes and the percentage of polymeric anthocyanins in wine samples. In 2021, PCA indicated PC1 accounted for 29.9%, and PC2 accounted for 22.2% of the total variance. The C0 treatments again separated from shade film treatments, but less so than in 2020. The separation in PC1 was again explained by the ratio of di- to tri-hydroxylated anthocyanins, along with the total glucosides, total methylated anthocyanins and total anthocyanins. The separation of C0 was along PC2 and thus was associated with higher concentrations of flavonols, terpenes, norisoprenoids, and polymeric anthocyanins in wine. We analyzed the relationships further between the variables monitored with a correlation analysis in wines . In 2020, CI in wines had the strongest positive correlation with TPI and acids. Alcohol percentage and ketones were also positively correlated to TPI and acids, although less so than CI. Ketones also were very strongly positively correlated with higher alcohols, while higher alcohols were less strongly correlated to acids. Conversely, flavonols were strongly negatively correlated with acetate esters and other esters in wines. Norisporenoids and pH were less negatively correlated to acetate esters. Fatty acid ethyl esters particularly showed to be negatively correlated with TA. In 2021, the strongest positive correlations in wines were between total anthocyanins and total glucosides and total methylated anthocyanins .

Total coumarylated anthocyanins were significantly and positively correlated to total anthocyanins, methylated anthocyanins, and total glucosides. Strong negative correlations were found between hue and ester compounds including fatty acid ethyl esters and acetate esters. Alcohol percentage and norisoprenoids were also negatively correlated witheach other. A strong negative correlation existed between the ration of di- to tri-hydroxylated anthocyanins and total acetylated anthocyanins. Lastly, total higher alcohols and pH were strongly negatively correlated with each other.In hot viticulture regions, there is a desire to reduce excessive alcohol content in wines due to marketability and taxation concerns . Numerous studies have demonstrated that partial solar radiation exclusion is an effective method for reducing the amount of ethanol in wines by reducing TSS in shaded clusters . However, in the present study, C0 wines consistently had the lowest alcohol content and the lowest concentration of residual sugars in 2020 compared to shaded fruit, despite grapes at harvest having similar TSS values across the treatments . This may be due to the composition of sugars in the grape berry being affected by excessive cluster temperatures in C0 fruit. Sepulveda and Kliewer showed that heat stress at 40°C post-veraison decreases glucose and fructose in the grape berry. During heat wave events post-veraison, cluster temperatures in C0 reached a maximum temperature of 58°C, exceeding the point at which glucose and fructose content is altered . Additionally, the production of non-fermentable sugars such as arabinose, raffinose and xylose are known to be present in the grape berry . Genes involved in the production of these sugars have been shown to be upregulated under heat stress conditions in grapevine . While the grape berry is 95-99% glucose and fructose at harvest, these non-fermentable sugars are included in the metric of total soluble solids . As a result, while TSS was unaffected by shade films , the proportion of fermentable to nonfermentable sugars may be impacted, thus leading to 2020 C0 wines with reduced alcohol content. This difference in alcohol content between 2021 wines was not observed most likely due to the 2021 growing season being cooler with less GDDs than 2020 . While C0 wines in this study demonstrated lower alcohol content than shaded wines, black plastic garden pots previous literature corroborates cluster temperature reduction by partial solar radiation exclusion as an effective method to lessen sugar content in the grape berry and thus reduce alcohol content of wines . The effect of partial solar radiation exclusion in semi-arid climates on berry pH and TA is mixed. Previous work demonstrates partial solar radiation exclusion to reduce pH and increase TA in grape berries by reducing the thermal degradation of organic acids . However, in the present study, berry pH and TA at harvest were unaffected in either year by shade films . Nonetheless, there were apparent effects on wine pH and TA that were vintage dependent. In the present study, D3 wines had the lowest pH and highest TA, while C0 wines did not differ from the shade films D1, D4 or D5 in pH or TA in 2020. Differences observed in pH between the wines ultimately affect the colorimetric properties of these wines.

In 2021, D4 and D5 wines showed the highest pH values. It is understood that the pH of the wines can shift the anthocyanin equilibrium in wine solution between the flavylium and quinoidal base forms . In the present study, D4 wines had the highest pH and the highest CI. In many cases, when pH rises, CI will decline as anthocyanin equilibrium shifts away from the flavylium form towards the colorless quinoidal forms . However, this was not the case in the present study. Rather, improved color intensity at elevated wine pH could be attributed to co-pigmentation in the wine matrix. Co-pigmentation refers to non-covalent interactions between anthocyanins and cofactors such as flavonols, flavan-3-ols and proanthocyaninidins, that results in greater absorbance of the wine than color what would be indicated by anthocyanin content and pH conditions . In the hotter 2020 vintage, the total flavonols in grape berries were increased in D4 fruit compared to other treatments . This increased berry flavonol content was transmissible during winemaking, as D4 wines also showed the highest total flavonols with similar concentrations as C0 wines in 2020. TPI was also enhanced in D4 wines. As such, this increased the abundance of cofactors in the wine matrix. Thus, improved color intensity documented in D4 wines in both vintages could be due to the enhancement of absorbance from increased flavonol content by reducing thermal degradation in the vineyard . In the cooler 2021 growing season, shade films produced wines with less flavonols than C0, but greater anthocyanin content, thus leading to improved color intensity in D4 wines. The increase of phenolic cofactors in D4 wines not only enhanced color and hue, but also led to a higher percentage of polymeric anthocyanins when compared to other shade treatments. Phenolic and polyphenolic compounds from grape skins and seeds can form polymeric pigments in wine with anthocyanins . These polymeric anthocyanins are more stable than monomeric anthocyanins and help to stabilize wine color. This occurs as the proportion of monomeric anthocyanins decreases, leaving color to be maintained by polymeric anthocyanins . Across both vintages, the percentage of polymeric anthocyanins was maximized in D4 wines, indicating that these wines may have greater aging potential than wines from C0 and other shading treatments.In the present study, partial solar radiation exclusion modified the composition of anthocyanins in wine. Partial solar radiation exclusion resulted in increased anthocyanin glycosides in wine from shade film treatments except for D4 wines in 2020. In 2021, D4 consistently showed the lowest cluster temperatures post-veraison and as a result, demonstrated the highest concentration of glucosides in resultant wines. Excessive berry temperatures post-veraison in both vintages led to C0 fruit with reduced total anthocyanin content atharvest and this carried over into resultant wines . The reduction of near-infrared radiation by at least 15% produced a cluster temperature conducive to anthocyanin accumulation, as these compounds are susceptible to thermal degradation above 35°C . When comparing total anthocyanin and flavonol concentrations between 2020 and 2021, regardless of treatment, 2020 wines had anthocyanin and flavonol concentrations six to seven times less than those in 2021 wines. As flavonoids are susceptible to thermal degradation, this drastic difference in total flavonoid concentrations may be attributed to hotter vintage air temperatures in 2020 compared to 2021.