## 4 Discussion
### Grape Juice Composition at Harvest  
[PERSON] et al. (2018) modeled an optimum growing season average temperature for high quality white wines, originating from Rhine Valley of 15.6 \({}^{\circ}\)C. The average growing season temperature at Geisenheim across the vintages 2017 to 2019 (16.7 \({}^{\circ}\)C) exceeded the optimum temperatures by 1.1 \({}^{\circ}\)C. Similarly, projections made by [PERSON] et al. (2018) forecast an increase in temperature during ripening by 1 \({}^{\circ}\)C in the period 2010 to 2040, and even by 6.3 \({}^{\circ}\)C in the period 2073 to 2099, compared to years with favorable sugar accumulation for cv. Riesling between 1976-2008 in Alsace, France. However, high average daily temperatures were recorded in the bunch zone of VSP (2018: 19.2 \({}^{\circ}\)C; 2019: 19 \({}^{\circ}\)C) and in the canopy of SMPH (2018: 19.4 \({}^{\circ}\)C; 2019: 19.1 \({}^{\circ}\)C) during ripening period of VSP beginning from 15 th of August until 19 th and 17 th of September in 2018 and 2019 respectively (Table S6). Although leaves shaded bunch zone of VSP and data logger were positioned approximately 30 cm higher in the SMPH canopy, temperature differences were marginal higher in SMPH (+0.1 \({}^{\circ}\)C to +0.2 \({}^{\circ}\)C). Interestingly, average temperatures in the extended ripening period of SMPH (2018: 24 th of September-10 th of October; 2019: 18 th of September-9 th of October.) were 6.5 \({}^{\circ}\)C (2018) to 7.1 \({}^{\circ}\)C (2019) lower, revealing that ripening at least partly occurred under moderate temperatures in SMPH. Nevertheless, VSP and SMPH yielded comparable TSS concentration, while commercial harvest was conducted 10 days (2017), 20 days (2018) and 22 days (2019) later in SMPH, compared to VSP. All thinning treatments increased grape juice sugar accumulation during ripening, but the treatment effects were not as clear in the harvested juice. This may be due to the fact that _B. cinerea_ incidence and severity differed among treatments in 2017 and 2019. In 2018, where no bunch rot was observed, grape juice TSS in SMPH were linearly correlated to yield, with SMPH BT increasing TSS by about 1.7 \({}^{\circ}\)Brix at 47.6% yield reduction, compared to SMPH. The grape juice of SMPH trained vines generally showed a higher TSS to TA ratio than that of VSP trained vines, and a higher tartaric to malic acid ratio. High TSS to TA ratios were determined by [PERSON] and [PERSON] [56] in high cropping table grapes of Thompson Seedless cultivar. Moreover, [PERSON] et al. [37] concluded that higher TSS to TA ratios in the presence of higher yield was due to a lower TA relative to a target TSS during ripening. Since tartaric acid and malic acid accumulation is dependent on carbon sources as well as glucose [57], lower TA could be explained by limited carbon sources (leaves) in response to trimming and/or leaf removal after fruit set. Assuming that TSS accumulation is not affected by leaf removal, due to a compensation response, resulting in an increase in photosynthetic activity and mobilization of reserve carbohydrates [17; 58], TSS to TA ratio is consequently increased. Conversely, [PERSON] et al. [37; 38] found decreased TSS to TA ratios by manipulating leaf area to fruit weight ratio through leaf and crop removal, as well as lower canopy height (\(-30\%\) to \(-60\%\)), predominantly caused by reduced TSS accumulation. The higher tartaric to malic acid ratio in SMPH may be explained by the higher light exposure of SMPH bunches, which increased the berry temperature, leading to an accelerated respiration of malic acid, as well as smaller berry size, which intrinsically led to an elevated tartaric to malic acid ratio in Riesling [58]. Low concentrations of malate were also related to low water status pre-veraison by [PERSON] and [PERSON] [59].