Enology – General Winemaking Session

Aude A. Watrelot* | Claudia Arriaga | Miguel Pedroza

Integrating Grape Stems into Red Winemaking: Consequences for Wine Quality

Aude A. Watrelot,* Claudia Arriaga, and Miguel Pedroza

*Iowa State University, 536 Farm House Lane, Ames, IA, 50011, watrelot@iastate.edu

An increased interest in the use of grape stems in winemaking has emerged, yet their actual impact on wine quality remains understudied, despite stems being rich in fiber and phenolic compounds. Given the potential of whole-cluster fermentation to increase tannin concentration, particularly in wines from interspecific grape cultivars, this study evaluated the effect of adding stems under fresh and dry form from two grape cultivars on Marquette and Frontenac wine quality. In 2023, Marquette and Frontenac grapes were crushed and destemmed and the stems were collected and either kept fresh, oven-dried or oven-dried and ground prior to addition to the musts. A control treatment without stems was included for comparison. In 2024, the same treatments were used in addition to using stems from Itasca grape cultivar in Marquette musts. Frontenac and Marquette wines were made following a standard red winemaking protocol. Chemical parameters including color, and phenolics composition and concentration were evaluated in Marquette and Frontenac wines throughout the process. The aromatic profile was evaluated on wines after 7 mo of aging by gas chromatography-mass spectrometry and a sensory descriptive analysis was performed at the same time. In Frontenac wines, dry ground stems yielded the highest anthocyanin and flavanol concentrations, while whole cluster wines were the richest in tannins. In 2023 Marquette wines, fresh and dry ground stems significantly increased iron-reactive phenolics and flavanol concentrations relative to the control. Methyl salicylate (wintergreen/rootbeer) was identified as a marker for fresh stem addition in both Frontenac and Marquette wines, with odor activity values (concentration/threshold) ranging from 2 to 3.5. Overall, stem additions altered the extraction of non-volatile and volatile compounds and led to wines that were hotter and drier, highlighting their potential to significantly modulate wine style.

Funding Support: U.S. Department of Agriculture (USDA) Agricultural Marketing Service 23SCBPIA1187 and SCBP24000621 (CFDA # 10.170 ” Specialty Crop Block Grant Program – Farm Bill)

Amanda Fleming | Renee Threlfall* | Erich Leitner

Assessing Aroma of Wines Produced from Cofermentation of Noble (Vitis rotundifolia) and Merlot (Vitis vinifera) Grapes

Amanda Fleming, Renee Threlfall,* and Erich Leitner

*University of Arkansas, 2650 N. Young Ave, Fayetteville, AR, 72704, rthrelf@uark.edu

While Muscadine grapes (Vitis rotundifolia Michx) used for wine production can have issues with color and phenolic stability, they contain unique aromas and flavors. Noble (V. rotundifolia) and Merlot (Vitis vinifera) grapes were harvested to investigate cofermentation, fermenting two or more grape varieties together, to enhance wine quality. After harvest, the grapes were randomized into five cofermentation treatments in duplicate (100% Noble, 75% Noble + 25% Merlot, 50% Noble + 50% Merlot, 25% Noble + 75% Merlot, and 100% Merlot), processed, and fermented. Volatile compounds were analyzed at bottling via solid-phase microextraction-gas chromatography-mass spectrometry (SPME-GC-MS). Five sensory panelists identified aromas of the 100% Merlot, 100% Noble, and 50% Merlot + 50% Noble wines by gas chromatography-olfactory-flame ionization detection (GC-O-FID). In 2024 wines, 77 volatile compounds were identified, including esters (32), higher alcohols (21), terpenes (4), ketones (3), glycols (2), sulfides (2), and lactones (1). Total volatiles ranged from 73,328 ug/L (100% Noble) to 89,358 ug/L (100% Merlot). Increasing Noble in treatments shifted the aroma profile toward aldehydes, terpenes, higher alcohols, and esters contributing waxy, soapy, green, floral, fruity, and citrus aromas. Wines with Merlot were characterized by esters, higher alcohol, ketones, and acids, contributing, fruity, apple, honeyed, nutty, fermented and wine-like aromas. GC-O-FID analysis showed that 100% Noble wine was characterized by strawberry and apple juice aromas, contributed by esters, 100% Merlot wine was distinguished by red berry, leafy, herbal, and fatty aromas, contributed by a combination of acids, esters, and higher alcohols, while 50% Merlot + 50% Noble wine had alcohol/solvent, melted butter, butterscotch, citrus, and wine-like aromas contributed by terpenes, esters, aldehydes, higher alcohols, and ketones. While postfermentation or prebottling blending is common for improving wine quality, cofermentation can achieve benefits earlier in production while enhancing the consumer appeal of Muscadine wines by leveraging their unique aromas.

Funding Support: Southern Region Small Fruit Consortium

Application of Alternative Enological Regimens for Aromatic Enhancement of Vidal Table Wine

Reid Ball, Jennifer Kelly, Shufen Xu, Dave Bowman, Dustin Duncan, and Debbie Inglis*

*Brock University, 1812 Sir Isaac Brock Way, St. Catharines, ON L2S3A1, Canada, dinglis@brocku.ca

Vidal blanc is grown widely for Icewine production in Ontario, Canada, but local industry has expressed interest in enological techniques to enhance volatile thiols in table wine made from this grape. To assess the impact that increased fermentation temperature, yeast strain, and yeast micronutrients have on Vidal wine aroma, seven fermentation treatments were tested: a control using Saccharomyces cerevisiae EC1118 at 14°C without Stimula Sauvignon blanc, S. cerevisiae Sauvy with and without Stimula Sauvignon blanc at 14°C, S. cerevisiae Sauvy with and without Stimula Sauvignon blanc at 20°C, and S. cerevisiae Sauvy with and without Stimula Sauvignon blanc with a temperature regime that went up to 26°C for one day. Sixteen aromatic compounds were quantified in the resulting wines using gas chromatography-mass spectrometry. Only one analyte, hexanol, was significantly higher in the control than in the treatments. Ethyl acetate, 2-methylpropanol, ethyl isobutryate, isoamyl acetate, and 2-phenylethyl alcohol were significantly higher across the treatments than in the control. Varying differences for the remaining compounds were seen between treatments, but general trends showed that the 26°C temperature regimen wines tended to have significantly greater concentrations of the measured compounds than wines from other treatments. Sensory bench trials confirmed that wines from the 26°C temperature regime had the most favorable aroma profile. Preliminary work for volatile thiol analysis via liquid chromatography-tandem mass spectrometry has indicated the presence of 3-mercaptohexanol in the samples. Quantification of this compound, as well as of 3-mercaptohexyl acetate and 4-mercapto-4-methyl-2-pentanone, is currently underway. Building on these results, additional commercial yeast strains and a locally isolated non-S. cerevisiae yeast strain are now being trialed with Vidal using the 26°C temperature regime supplemented with Stimula Sauvignon blanc.

Funding Support: Ontario Grape and Wine Research Inc.; Canadian Grapevine Certification Network.

Nicholas Wendrick | Sofia Torres | Andrew MacIntosh | Katherine Thompson-Witrick*

Chemical Changes in Carbonated Blueberry Wine Packaged in Three Materials Under Ambient Storage Conditions

Nicholas Wendrick, Sofia Torres, Andrew MacIntosh, and Katherine Thompson-Witrick*

*University of Florida, 586 Newell Dr., Gainesville, FL, 32611, kthompsonwitrick@ufl.edu

Blueberry wine is a fruit-based alcoholic beverage with a sensory profile influenced by chemical components that can interact with packaging materials, which serves a critical role in preserving wine quality. As alternative packaging formats gain popularity, there is a research gap regarding their effects on wine. This study compared the chemical stability of carbonated blueberry wine packaged in aluminum cans, polyethylene terephthalate (PET) bottles, and glass bottles under ambient storage. To test this objective, blueberry wine, ready for market, was packaged in each format and stored at 25°C for 240 days. Package performance was assessed for pH, titratable acidity, soluble solids, density, and alcohol, and no significant package-dependent differences were observed during storage (p > 0.05). Color stability varied by package: color intensity and hue measurements showed significant differences, with cans outperforming glass and PET. After 240 days, anthocyanin concentration was significantly higher (p < 0.05) in cans (49 mg/L) than in glass (44 mg/L) or PET (32 mg/L), indicating improved color retention. Free and total SO₂ varied with storage and differed by package at Day 240 (p < 0.05), with more free SO₂ retained in cans (40 mg/L) than in glass (25 mg/L) or PET (14 mg/L). Volatile organic compounds (VOCs) were summarized by class (alcohols, acids, aldehydes, esters, terpenes, and related compounds) and quantified as total VOC concentration (mg/L), providing an integrated indicator of aroma compound stability. Total VOCs differed by package (p < 0.05), with cans maintaining the highest concentrations compared to glass or PET. Overall, aluminum cans exhibited the smallest chemical deviations during ambient aging compared to PET and glass, which had more color, anthocyanin, SO₂, and VOC degradation; thus, aluminum cans are a viable alternative packaging material for carbonated blueberry wine.

Funding Support: Florida Department of Agriculture and Consumer Services

1:30 pm – 1:50 pm	Integrating Grape Stems into Red Winemaking: Consequences for Wine Quality Aude A. Watrelot, Iowa State University, Ames
1:50 pm – 2:10 pm	Assessing Aroma of Wines Produced from Co-fermentation of Noble (Vitis rotundifolia) and Merlot (Vitis vinifera) Grapes Amanda Fleming, University of Arkansas, Fayetteville
2:10 pm – 2:30 pm	Application of Alternative Enological Regimens for Aromatic Enhancement of Vidal Table Wine Reid Ball, Brock University, Canada
2:30 pm – 2:50 pm	Chemical Changes in Carbonated Blueberry Wine Packaged in Three Materials Under Ambient Storage Conditions Nicholas Wendrick, University of Florida, Gainesville

Enology – General Winemaking Session

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