Enology & Viticulture Joint Session – Influence of Vineyard Conditions and Practices on Wine

Pierre Davadant | Nataliya Shcherbatyuk | James A Harbertson | Lee A Kalcsits | Markus Keller*

Foliar Nitrogen Supplementation: A Tool to Manipulate Fruit N Status

Pierre Davadant, Nataliya Shcherbatyuk, James A Harbertson, Lee A Kalcsits and Markus Keller*

*Washington State University, 24106 N Bunn Road, Prosser, WA, 99350, mkeller@wsu.edu

Grapegrowers in dry regions face challenges with low nitrogen (N) in harvested grapes, affecting winemaking due to insufficient yeast assimilable nitrogen (YAN). Foliar N application at veraison may enhance grape and wine composition without inducing excessive vigor, yet its effect on phenolic compounds and plant N partitioning remain unclear. We conducted a 3-yr field trial and two separate pot experiments in arid eastern Washington to test whether foliar-applied N moves to the fruit and other plant organs, enhancing berry ripening and quality, and potentially replenishing the available N pool to support next year’s crop. In a field trial with own-rooted Syrah, we applied liquid urea ammonium nitrate (0, 22.5, 45, 90 kg N/ha) to the soil at bloom or foliar urea (15 kg N/ha) at veraison. We also tested the impact of supplementing a foliar urea spray at veraison (87 g N/L) on potted Cabernet Sauvignon vines that had received four different rates of soil N at bloom (0 to 3.75 g N per pot). Finally, using potted Riesling vines, we applied ¹⁵N-labelled urea at veraison on whole canopies, leaves only, or clusters only to trace N partitioning at harvest.

Results showed that foliar N application at veraison significantly increased YAN in field-grown Syrah and pot experiments. Higher YAN found in Cabernet Sauvignon-harvested berries was negatively correlated with skin tannins but not seed tannins. ¹⁵N applied on Riesling fruit remained in the clusters, while ¹⁵N applied on leaves was translocated to the perennial plant organs for storage. Pot experiments highlighted that the greatest relative increase in YAN from foliar N treatment occurred in vines with the lower N status.

Funding Support: USDA-NIFA Specialty Crop Research Initiative (award number 2020-51181-32159), Washington State Grape and Wine Research Program, Ste. Michelle Wine Estates (in-kind)

Juliana Pazos | Ryan Doyle | Markus Keller | Nataliya Shcherbatyuk | James Harbertson*

Vineyard Nitrogen Application Effect on Grape and Wine Phenolic Composition and Sensory Profile

Juliana Pazos, Ryan Doyle, Markus Keller, Nataliya Shcherbatyuk and James Harbertson*

*WSU Wine Science Center, 359 University Dr., Richland, WA, 99354, jfharbertson@wsu.edu

It was hypothesized that nitrate-based fertilizer treatments would lower fruit and wine phenolics due to increases in vine vigor and phenolic biosynthesis inhibition. 0, 20, 40, and 80 lbs nitrogen/acre were soil-applied to Syrah vines representing the Control, Low, Medium, and High treatments. In addition, a fifth treatment of foliar urea application (15 lbs N/acre) was included to contrast with the soil nitrate treatments. Treatments were applied to three different rows in a randomized block design. The experiment was repeated for three vintages (2022 to 2024). Wines were made respecting the block design (15 wines per vintage: five treatments, three replicates). Skin and seed tannin content, size, and composition were analyzed using protein precipitation and phloroglucinolysis. Sensory analysis was performed in the 2022 vintage using descriptive analysis. Eleven aroma, three taste, and three mouthfeel descriptors were evaluated in triplicate (tasting each treatment nine times) using a 15-person panel. Basic grape chemistry was not consistently altered by the vineyard treatments. Yeast assimilable nitrogen increased with the High and Urea treatments. Grape anthocyanins content, skins and seed tannin content, size, and composition were unaltered by the field treatments. However, High and Urea treatment wines presented significantly lower concentration of tannins than the Control and Low treatments. In addition, the High and Urea treatment wines had the lowest tannin size, although subunit composition was unaltered. Preliminary protein analysis using the BCA method suggests that higher soil nitrogen or foliar urea applications could lead to an increase in protein content, which could be binding to the larger tannins and remove them from the wine. Despite the significant differences in chemistry, panelists were unable to find significant differences between the wines.

Funding Support: Specialty Research Initiative High Resolution Vineyard Nutrition Project and Washington State Wine Commission

Caterina Szmania | Jochen Vestner | Ulrich Fischer*

Determination of Abiotic Stress-Induced Off-Flavors in White Wine by GC/Olfactometry and Sensory Reconstitution Studies

Caterina Szmania, Jochen Vestner and Ulrich Fischer*

*Institut for Viticulture & Enology, Dienstleistungszentrum Ländlicher Raum-Rheinpfalz, Breitenweg 71, Neustadt/67435, Germany, ulrich.fischer@dlr.rlp.de

Due to increasing abiotic stress, the atypical aging note (ATA) emerged in the late 1980’s, being reminiscent of naphthalene, floor polish, wet wool, fusel alcohols, and acacia blossom. Although 2-aminoacetophenone (2-AAP) was postulated as the molecular marker for the ATA taint, it only accounts for the “acacia blossom” scent, while the molecular base of the other off-flavors remains unknown. To fill this knowledge gap, 38 German white wines were analyzed, of which 21 were rejected due to an ATA off-flavor and 17 were approved. Descriptive analysis (DA) and non-targeted GC-analysis revealed significant differences between cohorts. GC/olfaction revealed overall 56 odor active volatiles, of which seven occurred at higher concentrations in rejected wines (negative contributors). Model wine and varietal wines (Riesling, Pinot blanc, and Müller-Thurgau) were either spiked solely with 2-AAP or a mix of all seven negative contributors at their greatest occurring concentration. DA showed that sole 2-AAP addition enhanced “acacia blossom” exclusively, while the attributes “ATA”, “fusel alcohol”, and “stressed” increased significantly only by adding all seven negative contributors. A sensory omission test revealed that among the seven negative contributors, only 2-methyl-propanol, 3-methyl-butanol, and methionol had a significant effect, which coincides with their highest odor activity values of 1111, 78, and 122, respectively. When adding only those three compounds to the model and varietal wines, DA reported equal “stressed”, “fusel alcohol”, and “ATA” intensities as if all seven negative contributors were added. Thus, the “classic” 2-AAP driven ATA-taint “acacia blossom” should be differentiated clearly from the stress-induced “fusel alcohol”, “atypical aging”, and “stressed” off-flavors caused by higher alcohols. They coincide with diminished fruitiness in the wines due to sensory masking and lower ester concentrations, which were presumably diminished by nitrogen/amino acid deficiency during grape maturation and in juices.

Funding Support: German Ministry for Economics and Climate Protection Research Council Food Industry (FEI), AIF 21 095 F

Qun (Kristy) Sun* | Quinn Cahoon | Shunping Ding | Shijian Zhuang

Effect of Biofungicides on Grape and Wine Chemistry, Fermentation, and Sensory Attributes of Wines from California

Qun (Kristy) Sun,* Quinn Cahoon, Shunping Ding and Shijian Zhuang

*California State University, Fresno, 2360 E Barstow Ave., Fresno, CA, 93740, qsun@csufresno.edu

Controlling common vineyard fungal pathogens such as Erysiphe necator (powdery mildew) and Botrytis cinerea (gray mold) is a significant concern for the grape and wine industry, particularly as these pathogens have developed varying degrees of resistance to synthetic fungicides. Biofungicides, which use other organisms to combat these pathogens, present a promising alternative. We evaluated the effects of biofungicides on grape and wine chemistry, wine fermentation, and sensory attributes. Chardonnay and Carignan from California’s Central Valley, along with Pinot noir and Chardonnay from the Central Coast, were treated with biofungicides in the vineyard and subsequently vinified during the 2023 and 2024 growing seasons. Treatments included three biofungicides: Bacillus subtilis strain QST 713 (Serenade ASO), Streptomyces lydicus strain WYEC 108 (Actinovate AG), and an extract of Reynoutria sachalinensis (Regalia). Two control treatments were used: one with a synthetic fungicide and one without any fungicide. All treatments were conducted in quadruplicate following a randomized complete block design. Berry and wine chemical components were measured comprehensively. Sensory evaluation was performed by a panel of 10 individuals consisting of students and staff from the Fresno State Viticulture and Enology department. Disease severity had the most significant affect. When disease pressure was minimal at a vineyard site, biofungicides were a viable alternative to synthetic fungicides, with their primary effect being on wine phenolic composition.

Funding Support: CDFA and ARI System