Carotenoids in grape berries have been shown to increase in berries with increased in solar radiation pre-veraison . However, under extreme exposure to heat and solar radiation, there is a documented decrease in carotenoid concentrations during ripening . To preserve the carotenoid concentrations in the grape berry and to promote C13-norisoprenoids in resulting wines under more frequent heat wave events and increases in air temperature, artificial shading with black polyethylene cloth has been trialed and found that shaded fruit contained more carotenoids than unshaded fruit . However, the effect of partial solar radiation exclusion on wine C-13 norisoprenoid content seems to be more nuanced. Wines produced from the shaded fruit contained more b- damascenone as well as esters compared to wines produced from unshaded fruit . Yet, there are conflicting reports showing no effect of UV exposure on b- damascenone concentrations in Shiraz wines made from clusters that underwent solar radiation exposure via varying rates of leaf removal and polycarbonate UV screens . Like C13-norisoprenoids, final terpene concentrations in wines depends on the net accumulation in grape clusters exposed to excessive temperatures and UV radiation . The effect of photoselective overhead shade films on whole plant physiology and temporal development of berry flavonoids of Cabernet Sauvignon development over two growing seasons was previously studied in a hot region .

Grape berries growing under reduced near-infrared radiation exposure in hotter than average years, large pots plastic resulted in a 27% increase in anthocyanin content at harvest than the exposed control due to decreases in anthocyanin degradation due to high berry temperatures . Moreover, flavonol degradation was similarly decreased, thus optimizing flavonol content in the grape berry under reduced near-infrared radiation exposure . The objectives of this study aimed to determine the extent to which the impact of photoselective overhead shade films on flavonoid development transfer to wine and the cascading effects of partial solar radiation exclusion had on aroma composition of resultant wines.The experiment was conducted in Oakville, CA, USA during two consecutive growing seasons at the University of California Davis, Oakville Experimental Vineyard. The vineyard was planted with “Cabernet Sauvignon” clone FPS08 grafted onto 110 Richter rootstock. The grapevines were planted at 2.0 m × 2.4m and oriented NW to SE. The grapevines were trained to bilateral cordons, vertically shoot positioned, and pruned to 30-single bud spurs. Irrigation was applied uniformly from fruit set to harvest at 25% evapotranspiration as described elsewhere . The experiment was arranged in a randomized complete block with four replications. The photo selective shade film treatments were previously described in Marigliano et al. and their properties presented in Figure 1. Shade films were designed to target portions of the electromagnetic spectrum previously observed and measured at the experimental site . Briefly, four photo selective shade films and an untreated control were installed in 3 adjacent rows on 12 September 2019. The shade films remained suspended over the vineyard until 20 October 2021.

The shade films were 2 m wide and 11m long and were secured on trellising approximately 2.5 m above the vineyard floor. Each experimental unit consisted of 15 grapevines in 3 adjacent rows. Grape clusters were harvested by hand from each experimental unit when berry total soluble solids reached 25o Brix on 9 September 2020, and 7 September 2021, respectively.Vinification was conducted in 2020 and 2021 at the UC Davis Teaching and Research Winery. Upon arrival at the winery, grapes were destemmed and crushed mechanically. Must from each field experimental unit was divided into three technical fermentation replicates . K2S2O2 was added to each treatment replicate and must was allowed to cold-soak overnight at 5o C in jacketed stainless-steel tanks controlled by an integrated fermentation control system . The following day each treatment-replicate was inoculated with EC-1118 yeast to initiate fermentation. Musts were fermented at 25°C and two volumes of must were pumped over twice per day by the integrated fermentation control system. During the winemaking process, TSS was monitored daily using a densitometer and fermentations were considered complete once residual sugar contents were less than 3 g L-1. Wines were then mechanically pressed using a screw-type basket press. Following pressing, wine samples were collected for flavonoid analysis. Malolactic fermentation was initiated with the addition of Viniflora® Oenococcus oeni . Malolactic fermentation was carried out at 20o C. Upon completion of MLF, free SO2 levels were then adjusted to 35 mg L-1 and wines were bottled.Using a spectrophotometer , color intensity , hue, total polyphenolic index and % of polymeric anthocyanins was determined following procedures described by Ribereau-Gayon, Glories, Maujean, and Dubourdieu .

Wine samples were diluted in water and absorbance readings were taken at 280, 420, 520, and 620nm. The absorbance at 740 nm was subtracted from all absorbance readings to eliminate turbidity. CI was calculated as the sum of absorbance at 420, 520 and 620nm. Hue was calculated as the ratio between the absorbance at 420 and 520nm. The percentage of polymeric anthocyanins was determined via absorbance measurements at 520nm after anthocyanin bleaching with a sodium bisulfite solution . TPI was determined by diluting wines with water and recording absorbance at 280nm.Wine flavonoid composition was determined following procedures previously described . Briefly, wine samples collected after pressing were centrifuged at 5,000 rpm for 10 mins, filtered with PTFE membrane filters and transferred to high performance liquid chromatography vials prior to injection. An Agilent 1260 series HPLC system with a reversed-phase C18 column was used to simultaneously determine the anthocyanin and flavonol concentrations. The mobile phase flow rate was 0.5 mL min-1, and two mobile phases were used, which included solvent A = 5.5% aqueous formic acid; solvent B = 5.5% formic acid in acetonitrile. The HPLC flow gradient started with 91.5% A with 8.5% B, 87% A with 13% B at 25 min, 82% A with 18% B at 35 min, 62% A with 38% B at 70 mins, 50% A with 50% B at 70.01 min, 30% A with 70% B at 75 min, 91.5% A with 8.5% B from 75.01 min to 91 min. The column temperature was maintained at 25o C. This elution allowed for avoiding co-elution of anthocyanins and flavonols as previously reported . Flavonols and anthocyanins were quantified by determining the peak absorbance at 365nm and 520nm, respectively. Quercetin 3-O-glucoside and malvidin chloride were used as quantitative standards.Volatile compounds in wine samples were analyzed following procedures described previously . Briefly, 10-mL of each wine sample was transferred to a 20-mL amber glass vial . Each vial also contained 3 g of NaCl and 50mg of an internal standard solution of 2-undecanone . After agitating at 500 rpm for 5 mins at 30o C, samples were exposed to 1 cm polydimethylsiloxane/divinylbenzene/ Carboxen , 23-gauge SPME fiber for 45 mins. Helium was used as a carrier gas at a flow rate of 0.8636 mL/min in a DB-Wax 231 ETR capillary column  with constant pressure and temperature at 5.5311 psi and 40o C, respectively. The oven temperature was kept at 40o C for 5 mins and then incrementally increased by 3o C/min until reaching 180o C. Oven temperature was then increased by 30o C/min until reaching 260o C, plant plastic pot at which temperature was maintained for 7.67min. The SPME fiber was desorbed split mode with a 10:1 split for wine samples and held in the inlet for 10min to prevent carryover effects. The method was retention time-locked to the 2-undecanone internal standard. The total run time per sample was 61.67min. Electron ionization was performed with a source temperature of 230o C and the quadrupole at 150o C. The wine samples were measured using synchronous scan and selected ion monitoring . The mass spectrometer scanned from m/z 40 to 300. Compounds were detected using between two and six selected ions. Data was analyzed using MassHunter Qualitative Analysis software . After normalization with 2-undecanone internal standard, results were expressed as peak areas. Compounds were tentatively identified in the mass spectrometry spectrum of the peaks and confirmed by comparison to the National Institute of Standards and Technology database . The ions used SIM for each compound and retention times were reported previously by . The odor activity value thresholds were obtained from a selected review of published literature of young red wines and were used in comparing the monitored compounds .Statistical analyses were conducted with R Studio version 4.0.5 for Windows. All data were subjected to the Shapiro-Wilk’s normality test. Data was subjected to two-way analysis of variance to assess the statistical differences between the applied shade film vineyard treatments and the vintage and their combination. Means ± standard errors were calculated and when the F-value was significant , a Duncan’s new multiple range post-hoc test was executed using “agricolae” 1.2-8 R package . Principal component analysis was conducted and visualized with the same software, using the “factoextra” package . Pearson correlation analyses were performed with using the same software with the “corrplot” package .Meteorological data collection and climactic conditions at the experimental site for the 2020 and 2021 growing seasons are described in detail by Marigliano et al. .

Briefly, there were 1762.7°C growing degree days accumulated in 2020 compared to 1572.3°C GDDs accumulated in 2021, with similar GDD accumulation from April to June in both years. Compared to the 10-year average , the 2020 growing season accumulated more growing degree days by 1 October. The 2021 growing season was a cooler year with less accumulated GDD than the 10-year average. The total precipitation at the experimental site from 1 March 2020 to 30 September 2020 was 84.1mm, a notable 100.5mm less precipitation than the 10-year average for the experimental site. Drought conditions continued into the 2021 water year, with 66.9 mm of precipitation between 1 March 2021 and 30 September 2021. Precipitation only occurred in March and April 2021 and was negligible in the following months. Given the severe drought conditions in both experimental years, precipitation had a negligible effect on plant water status in control and shaded treatments with 25% ETc replacement, as demonstrated by no significant effects on stem water potential integrals between control and shaded treatments in either experimental year .Grapes resulting from field treatments were vinified under the same conditions in both years. In 2020 alcohol content was the highest in D1 and D4 wines , while alcohol content and residual sugar concentration was lowest in C0 in 2020. All shade film wines contained more alcohol and residual sugar than C0. In 2021, alcohol content and residual sugar concentration was unaffected across all wines. In 2020, pH was only decreased in D3 wines. In 2021, C0 wines had the lowest pH compared wines from shaded grapes. Among the shaded treatments, D4 and D5 wines had higher pH compared to D1 and D3 wines. In 2020, titratable acidity only increased in D3 wines compared to C0, D1 and D5 wines. C0, D1, D4 and D5 wines were indistinguishable in titratable acidity. While C0 had one of the lowest values for TA in 2020, C0 wines in 2021 had one of the highest TA values, along with D3 and D5 wines. The lowest TA value was observed in D4 wines from 2021. Color intensity within the 2020 wines varied considerably, with the D4 having the greatest value for CI . In 2021, D4 again had the highest values for CI, while the remaining wines were statistically not different from each other. Hue decreased only in D3 wines during the 2020 vintage, while there was no effect of shade films of wine hue during the 2021 vintage . D1 and D4 had the highest percentage of polymeric anthocyanins, while D5, D3 and C0 wines had less . In 2020, D1 and D4 wines had higher TPI values compared to C0 and D3 wines. In 2021, TPI of wines was not affected by shade films except for D4.Wine anthocyanin profiles were separated into glucosides, 3- acetylated and coumarylated anthocyanins . The total free anthocyanin concentration was the lowest in C0 wines compared to shade film treatments in 2020. Concentrations of 3-glucosides and 3- acteylated glucosides increased for all anthocyanins under shading treatments compared to C0, with the exception of peonidin 3-acetylglucoside and cyanidin 3-glucoside in which shading treatments had no effect. The composition of coumarylated 3’4’5’-hydroxylated anthocyanin modifications was largely impacted by shading, with the largest concentrations detected in C0, D1 and D5 wines. Overall, the ratio of di- to tri-hydroxylated anthocyanins was the largest in C0 wines and the lowest in D5.