Sunlight exposure of winegrape clusters is frequently reported to increase C(13)-norisoprenoids in resulting wines, but the timing and mechanism of this influence is not well understood. Fruit zone leaf removal was applied to Vitis vinifera cv. Riesling at three timings: 2, 33 and 68 days past berry set (PBS), and compared to an untreated control. Free and total 1,1,6-trimethyl-1,2-dihydronaphthalene (TDN), vitispirane and beta-damascenone were measured in juice and wines, and carotenoid profiles were determined in grapes at midseason and maturity. Significantly higher total TDN was observed in grapes from the 33-day PBS treatment compared to the control and other treatments (195 microg/L vs 54-87 microg/L). Total vitispirane in juice was also significantly increased in the 33-day PBS treatment, while total beta-damascenone was reduced in the 68-day PBS treatment compared to the control. Existing HPLC protocols were modified to allow for quantification of zeaxanthin in V. vinifera berries, and zeaxanthin was determined to be significantly higher in the 33-day PBS treatment than the control or other treatments (p < 0.05). Total TDN in juice correlated with free TDN in wine, with 11.0% +/- 2.5% of total juice TDN converted to free TDN in wine. In contrast, total vitispirane increased significantly during fermentation, and was not correlated with vitispirane in juice. In summary, leaf removal at 33 days PBS significantly increased zeaxanthin in Riesling grapes midseason, total TDN and vitispirane in the juice of mature Riesling grapes, and free and total TDN in finished wine, while earlier or later leaf removal had no effect.

The treatments had variable impacts on wine anthocyanin, berry skin tannin, berry seed tannin, and wine tannin depending on year. Wine tannin (42 to 64 mg/L) and tannin extractability (5 to 6%) were both very low compared to values typically observed in red wines produced from V. vinifera. Using a two-alternative forced choice test, panelists reported ST+CL wines were fruitier than the control and ST wines and that ST wines were less fruity than the control in both years. An economic analysis indicated that in order for growers/wineries to maintain their economic welfare, bottle prices would have to increase by $0.02 to $0.41 depending on the practice and year to compensate for additional labor costs and lost yield in implementing these crop-load management practices.

The microbiome of a vineyard may play a critical role in fruit development, and consequently, may impact quality properties of grape and wine. Vineyard management approaches that have directly manipulated the microbiome of grape clusters have been studied, but little is known about how vineyard management practices that impact the soil microbial pool can influence this dynamic. We examined three under-vine soil management practices: 1) herbicide application, 2) soil cultivation (vegetation removal), and 3) natural vegetation (no vegetation removal) in a Riesling vineyard in New York over a three-year period. The microbiomes associated with soil and grapes were profiled using high-throughput sequencing of the bacterial 16 S rRNA gene and fungal ITS regions. Our results showed that soil bacterial composition under natural vegetation differs from that seen in glyphosate-maintained bare soil. Soil fungal composition under the natural vegetation treatment was distinct from other treatments. Although our study revealed soil microbiome shifts based on under-vine management, there were no corresponding changes in fruit-associated microbial composition. These results suggested that other vineyard management practices or environmental factors are more influential in shaping the grape-associated microbiome.

No abstract

No abstract