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Viticulturists and winemakers utilize wine grape cultivar clones in order to achieve specific goals related to yield, quality, and wine characteristics. Vitis vinifera cv. Petite Sirah, also known as Durif, is an important wine grape cultivar in California in the production of varietal wines and as a means to improve the color/tannic structure of red wines through blending. Four Petite Sirah clones (FPS01, FPS03, FPS04, and FPS05) were evaluated to compare their agronomic performance and grape and wine characteristics over the course of the 2021 growing season. Eighty vines of each of the four clones were each organized into four biological replicates in a randomized block design at the Robert Mondavi Institute vineyard (Davis, CA). Five vines per biological replicate were evaluated for vine water status, canopy density, ripening parameters, veraison progression, harvest must chemistry, and cluster condition. Clones were harvested at similar ripeness levels, yields determined, and winemaking performed in triplicate. Both the grape and wine phenolic profiles were determined by the Adams-Harbertson Assay and reversed-phase high-performance liquid chromatography (RP-HPLC). Grape and wine aroma profiles were determined by used head space-solid phase micro extraction-gas chromatography-mass spectroscopy (HS-SPME-GC-MS). Wine phenolic extraction during fermentation was monitored daily by spectrophotometric measurements. Results indicate that clones FPS01 and FPS04 may ripen and accumulate sugar quicker than FPS03 and FPS05 depending on the growing season. Grape must from FPS05 contained higher level of malic acid while FPS03 contained the lowest. FPS03 wines had least amount of phenolic compounds in comparison to other clones as they contained the lowest amount of flavan-3-ols, anthocyanins, and flavonols. Wines from FPS01 and FPS04 were higher in flavan-3-ols and flavonols respectively. Grapes and wines from each clone also showed differences in the composition of volatile compounds. Therefore, it can be stated that differences in chemical composition exist among Petite Sirah clones. In this specific year, these chemical differences did not translate to clear, significant differences in sensorial perception based on descriptive analysis.

Grapevines (Vitis species) are grown worldwide to produce table grapes, juice grapes, dried grapes, and wine with the United States as one of the world’s largest wine and grape producers. Though not a large contributor to the U.S. grape and wine industry, Arkansas’ industry plays an important role in the state’s agritourism and economy. Most grapes grown in Arkansas’ warm climate include native species, such as muscadines (V. rotundifolia) and hybrids (crosses of Vitis species). Two important hybrid red wine grapes grown in Arkansas are Chambourcin, grown commercially for its positive viticulture and enological quality, and Enchantment, a newer cultivar with potential in this region. Since acidity of grapes is impacted by the climate of the region, there is interest in using non-Saccharomyces yeast, such as Lachancea thermotolerans, for wine production to modify acidity and other wine attributes. Additionally, quality of grapes and wines produced in Arkansas impact consumer awareness, perception of and advancement of the local industry. Thus, the objectives of this research were to evaluate the use of non-Saccharomyces yeasts to modify acidity in wine fermentations from grapes grown in Arkansas and investigate the impact of the Arkansas Quality Wine Program on perception and quality of Arkansas wines and the Arkansas grape and wine industry. In 2020 and 2021, Arkansas grown Chambourcin and Enchantment grapes were harvested and fermented using S. cerevisiae (SC) without and with malolactic cofermentation (SC-MLF) and L. thermotolerans with a sequential inoculation of S. cerevisiae (LT-SC) without and with malolactic cofermentation (LT-SC-MLF). For Enchantment fermentations in 2021, two treatments (SC and LT-SC) were evaluated due to limited fruit. Evaluations of inoculation treatments were done on must/wine during fermentation, wine at bottling, and wine during storage. Treatments with L. thermotolerans impacted lactic acid levels of both varieties during fermentation but had a greater impact on organic acids and pH of Chambourcin than Enchantment, thus increasing potential for improved microbial and color stability. L. thermotolerans also had a greater impact on color attributes of Chambourcin wines from both years, compared to Enchantment wines. The 2020 Chambourcin wines were evaluated by sensory panels, which rated LT-SC and LT-SC-MLF wines higher than the other inoculation treatments for sourness. Although wines inoculated with L. thermotolerans were more sour, commercial wines can be adjusted at bottling to mediate sourness to increase consumer acceptability. In 2021 and 2022, an online consumer wine survey from the Arkansas Quality Wine Program (AQW) showed that consumers wanted to purchase Arkansas-made wines but were inhibited by a perceived lack of quality and desirability. An AQW wine competition was held in 2020 and 2021 with a total of 75 wines entered. Most wines submitted received high marks for gold, silver or bronze medal earnings. Competition wines with appropriate free and total sulfur dioxide levels, and lower volatile acidity, dissolved oxygen, and ethanol levels garnered higher medal earnings. Select medal-earning wines from the 2021 AQW competition were analyzed by a consumer sensory panel and for composition and color attributes. Wines that were semi-sweet to sweet were the most preferred despite higher volatile acidity levels. Through public outreach efforts in the form of virtual workshops for winemakers and wine education and tasting events, the AQW program reached nearly 1,000 individuals, both industry and non-industry from 2020 to 2022. Thus, efforts by Arkansas grape and wine producers to utilize new enological products, manage specific quality parameters in wines, and use targeted marketing strategies can increase consumer awareness of and quality of wines produced in Arkansas.

The accumulation of salts in plant rootzones, known as “salinization,” is often a gradual process that can degrade soil structure and cause permanent plant damage. Salinization caused by ever increasing water demands and an increasingly dry climate is becoming problematic for agriculture in semi-arid to arid regions, including California’s Central Valley, which produces about one-quarter of the United States' food supply and almost half of its nuts and fruits, including grapes, according to the USGS California website (https://ca.water.usgs.gov). While grapevines are considered moderately salt tolerant (Walker et al. 2002), the current rate of salinization in many of California's vineyards is contributing to reduced crop yields and lower fruit quality (Keller 2020). Once symptoms of salt toxicity appear on the leaves, vine growth and crop yield may already be in serious decline (Fort and Walker 2011). To prevent salt toxicity from occurring in grapevines, the Walker Lab at UC Davis is applying traditional plant breeding techniques to some of the native population of wild North American grapevine species to improve the salt tolerance of commercial rootstocks (Fort et al. 2013). In recent years, the Walker Lab discovered a wild grapevine species called Vitis acerifolia 9018, which has consistently proven to be more salt tolerant than the most salt tolerant commercial rootstocks (Chen 2021). These physiological traits could be bred into existing popular commercial rootstocks to improve their salt tolerance. The research for this thesis was performed to observe the stress response and compare the salt tolerance of the recently discovered salt tolerant wild rootstock V. acerifolia 9018, against commercial rootstocks widely planted in California and other salinization-affected places, including Ramsey, 1103 Paulson and 140 Ruggeri.

Sulfur-like off-aromas (SLOs) are reportedly responsible for nearly 30% of the faults identified in premium wines in competition. Hydrogen sulfide (H2S, “rotten egg aroma”) is most frequently reported in excess of its sensory threshold (~ 1 µg/L) in wines with SLOs. H2S can be produced during fermentation through several pathways but is sufficiently volatile such that the majority formed during fermentation will be lost to CO2 entrainment. After fermentation, winemakers may attempt to remove H2S by inert gas sparging, aeration to oxidize H2S or other VSCs, or addition of cupric (Cu[II]) salts to form non-volatile complexes. A convenient and inexpensive approach for analysis of H2S in wine samples was developed using common winery laboratory glassware and disposable, colorimetric, gas detection tubes. Excellent linearity is achieved using both proposed methods of operation, the N2 Method and the Aspiration Method. Limits of detection are comparable to those achieved using conventional analytical techniques. Recent work has further established that soluble copper-sulfhydryl complexes can serve as precursors for SLO development during wine storage. Copper-sulfhydryl complexes are disrupted in the presence of strong NaCl brine. The quantity of H2S released in this manner is correlated with H2S formation during bottle storage. The factors affecting the stability of these copper-sulfhydryl complexes and the release of H2S during storage are explored in this work and a brine dilution assay has been optimized for releasing H2S from copper-sulfhydryl complexes. Model and commercial wines were treated with copper, sulfide, and glutathione to form metastable copper-sulfhydryl complexes. In wines prepared with the addition of glutathione along with copper and H2S, up to 4-fold increase in recovery of H2S by brine dilution was achieved, compared to the control. Only a small portion of added H2S could by detected following addition of disulfide bond reducing agent (TCEP) suggesting that most of the unrecovered H2S likely formed more stable copper-sulfhydryl complexes. A growing concern for H2S formation is in canned wines and the phenomenon is credited to the reaction of SO2 in wine with aluminum metal. Evidence suggests this can occur even in the presence of a polymeric liner in the can. Considerable variation is observed in H2S production among canned wines with similar free SO2 concentrations, such that predicting the suitability of a given wine for aluminum packaging remains challenging. The initial development of an accelerated bench-test for predicting H2S formation is described, as well as its validation against real canned wine storage for up to eight months. In accelerated aging, negligible formation of H2S was observed in red wines (

In the United States and Canada, rapid growth in production and sales of alcoholic or “hard” cider has brought about a rapid increase in the number of acres planted with high-tannin apple (Malus ×domestica) cultivars, mostly of English and French origin. These cultivars, valued for the “mouthfeel” they confer to alcoholic cider, are often prone to “biennial” bearing, which is largely caused by seed-derived gibberellins suppressing floral bud formation, and thus return bloom. Crop load management, via bloom or fruitlet thinning, is often used to mitigate biennial bearing, as are bloom-promoting plant growth regulator (PGR) sprays. Four field experiments assessed the innate bearing habit, response to thinning, and response to bloom-promoting PGR sprays of seven high-tannin cider cultivars, as well as the effects of crop load on fruit maturity and juice quality. In a three-year hand-thinning experiment conducted in Lyndonville, NY (Chapter 2), biennial bearing index (BBI) correlated negatively with cumulative yield both within and among cultivars: ‘Chisel Jersey’, ‘Dabinett’, and ‘Harry Masters Jersey’ had low BBI and high cumulative yield overall, while ‘Michelin’ had higher BBI and somewhat lower cumulative yield; ‘Brown Snout’, ‘Binet Rouge’, and ‘Geneva Tremlett’s Bitter’ were highly biennial and unproductive overall. Hand-thinning reduced BBI over three years, but rarely achieved comparable or greater cumulative yields over three years. Fourth-year bloom data indicate that, had treatments been re-imposed, thinning would result in comparable or improved cumulative yield, and lower BBI, for four of seven cultivars. This experiment, and an identical experiment performed in the low-crop “off” year only on a different set of trees, indicate that thinning in the “off” year is not effective at promoting return bloom. The same two experiments found that crop load correlated negatively with polyphenol (i.e., tannin) content, soluble solid (i.e., sugar) content, titratable acidity, and nitrogen content, of juice over three years, for all seven cultivars (Chapter 3). The relationship between maturity and crop load was cultivar-specific. A concurrent three-year experiment (Chapter 4) found that PGRs were not effective at promoting return bloom in any of the same seven cultivars. Likewise, a two-year experiment (Chapter 4) conducted in Lansing, NY found that PGR sprays had no appreciable bloom-promoting effect either compared to or in combination with hand-thinning, in ‘Chisel Jersey’ or ‘Brown Snout’, but that crop load did have a significant negative effect on return bloom. A survey of commercial cidermakers in the United States and Canada (Chapter 5) found that biennial bearing affects apple supply for a majority of cidermakers growing their own high-tannin fruit, but only affects a minority of non-grower cidermakers working with high-tannin cider cultivars. Thinning and other horticultural practices to promote annual bearing were not commonly performed by high-tannin cider apple growers. The most mentioned cultivars by both apple growers and cideries who only purchase fruit or juice were the reputedly annual ‘Dabinett’ and the notoriously biennial ‘Kingston Black’. Inconsistent supply was the leading reason given by cidermakers who choose not to use high-tannin fruit in their cider. The work presented in this thesis demonstrates: the efficacy of hand thinning in certain high-tannin cider cultivars at promoting annual bearing, improved cumulative yields, improved juice quality, and overall tannin yield; the long-term profitability of thinning in high-density cider orchards for some cultivars; and the need for further research to identify effective midsummer PGR strategies that can be used with fruit thinning to promote return bloom in biennial high-tannin cider cultivars. Thinning to 9 fruit/cm2 TCSA can improve long-term productivity in ‘Brown Snout’, ‘Chisel Jersey’, ‘Dabinett’, and ‘Harry Masters Jersey’, and can improve long-term tannin production in all seven cultivars described in this thesis.

Over time and with oxygen ingress, the chemical composition of wine evolves through a cascade of reactions comprising many pathways, one of which yields acetaldehyde, an oxidation product which not only directly impacts wine aroma but also facilitates further reactions altering other sensory properties such as color and mouthfeel. Key reactions in this pathway are catalyzed by the redox cycling of iron between two oxidation states, iron(II) and iron(III), thus the majority of the work presented herein focuses on control of iron’s reactivity. A spectrophotometric method of iron speciation was developed as a means of monitoring the reciprocal processes of iron reduction and oxidation in wine. The method relies on the combined use of two opposing chelating agents, ferrozine and ethylenediaminetetraacetic acid (EDTA), iron(II)- and iron(III)-selective respectively, to halt redox reactions, thereby providing a stable measurement of iron(II):iron(III) ratios in wine. This method was used to investigate the redox cycling of iron in model wine as it occurs in the primary reactions of the oxidation pathway: the oxidation of iron(II) by oxygen and the reduction of iron(III) by phenols. The rates of both processes varied with changes to model wine composition, though the former was found to be consistently slower. This suggests that iron(II) oxidation is the rate-determining reaction for the wine oxidation pathway, and wine ages at a rate limited not necessarily by its chemical composition but by oxygen ingress. Despite this, different wines subject to the same oxidative conditions will often vary in their response to oxygen, thus the reactions of hydrogen peroxide, a key branchpoint further down the oxidation pathway, were investigated, specifically as influenced by complexation of iron by major wine acids (tartaric, malic, and citric). The rate of the iron(II)-catalyzed Fenton oxidation of ethanol into acetaldehyde was found to occur more quickly toward the upper limits of typical wine pH, an effect most apparent with citrate complexation of iron. This appeared to affect the efficacy of sulfur dioxide as an antioxidant in competing with iron(II) for hydrogen peroxide. In addition, acetaldehyde formation in wine was found also to depend on oft-overlooked biotic factors post-fermentation. In a series of experiments pertaining to micro-oxygenation, found critical to the process were residual sugar and populations of Saccharomyces cerevisiae, without which acetaldehyde production would not occur. The question of why acetaldehyde does not accumulate with oxygenation alone warrants further investigation.

Cleaning and sanitization are essential operations in wine production. The use of chemical cleaning and sanitizing agents for managing waste in fermentation vessels and the sulfur dioxide fumigation of empty oak barrels are ubiquitous processes in commercial wineries but are poorly studied in academic literature. Increasing environmental pressures and concerns over the poor quality of winery wastewater have created a need for optimizing protocols by reducing chemical inputs and water usage while maximizing the efficacy of treatments and employee safety during application. To optimize the use of chemical cleaning and sanitizing agents for managing fermentor waste the performance of a wide range of commercially available cleaning and sanitizing chemistries was assessed using fermentation derived soils and spoilage microorganisms in planktonic and sessile physiologies in trials from bench scale to 2000-L fermentation tanks. Minimum effective antimicrobial concentrations of chemical treatments were determined for common winery spoilage yeasts using the minimum inhibitory concentration, minimum biocidal concentration assay, and a modified minimum biofilm inactivation assay. Propidium iodide fluorescent staining was used to determine the minimum effective contact time required for inactivating Saccharomyces cerevisiae cultures using peracetic acid. Results suggested that caustic cleaning agents were the most effective in removing fermentation soils, and that sanitizers were ineffective without thorough prior cleaning. Peracetic acid- and hydrogen peroxide-based sanitizer formulations were effective and have innocuous breakdown products compared to traditional chemistries. Manufacturers’ suggested application rates were largely in line with the minimum effective antimicrobial concentration for the spoilage microorganisms tested. In practical settings, sanitary tank design may be the most important factor in determining the success of cleaning and sanitizing efforts regardless of the specific chemicals applied.The sulfur dioxide detection performance of colorimetric gas detection tubes, gas chromatography-sulfur chemiluminescence detection, and a novel electrochemical sensor apparatus was assessed. The electrochemical sensor was superior in linearity and precision versus the other detectors. American oak barrels were used to measure the persistence and antimicrobial efficacy of the sulfur dioxide fumigation of empty winery cooperage for pure gas application and the combustion of solid sulfur wicks. Prior to fumigation, the penetration rate and abundance of spoilage yeasts in barrel wood for cultures inoculated in grape must was determined for Saccharomyces cerevisiae and Brettanomyces bruxellensis cultures. S. cerevisiae cultures were recovered at 10 mm depth within one week of inoculation. B. bruxellensis cultures did not penetrate beyond surface samples within six weeks of inoculation. Measurable concentrations of sulfur dioxide existed after six weeks of storage for pure gas and sulfur stick fumigation, with concentration profiles closely described by power law functions regardless of the hydration status of the barrel wood. Both gas applications and sulfur stick combustion effectively eliminated culturable populations of S. cerevisiae and B. bruxellensis for all samples. Methods for assessing the mechanism of sulfur dioxide diffusion as a Fickian process according to the steady-state approximation poorly fit the measured gas data. Interactions between the diffusing gas and the stave wood and the heterogeneous structure of barrels may explain the discrepancy between the observed and predicted Fickian diffusive behavior. Together, this work presents the most comprehensive quantitative assessment of winery cleaning and sanitization to date in academic literature. These studies not only provide insight into the fundamental interaction of microorganisms, winery equipment, and chemical cleaners and sanitizers, but can also act as a practical resource for winemakers to develop effective cleaning and sanitizing protocols and monitoring strategies.

The aroma profiles of Riesling, Gewürztraminer, and Traminette grapes are largely derived from monoterpenes found in grape pulp and skin. To optimize the extraction of monoterpenes and other volatile compounds, a winemaking technique called pre-fermentation cold soak (CS) is sometimes used. Unfortunately, CS may also allow for the extraction of undesirable bitter compounds, including monomeric phenolics. To address this concern, monomeric phenolic concentrations were measured in wines produced with varying CS durations. Among the compounds analyzed, (+)-catechin and (-)-epicatechin were most affected by CS duration. Because total monomeric phenolic concentrations tended to increase with increasing CS duration, wine bitterness intensity was quantified by a trained panel. Sensory evaluation results, however, suggest that CS duration and bitterness intensity are not directly related. Following the CS study, detection thresholds of (+)-catechin and (-)-epicatechin in model and commercial wines were determined in order to learn more about the contributions of these compounds to wine sensory characteristics. (+)-Catechin detection thresholds in model and commercial wines were 205 and 278 ppm, respectively. In contrast, the detection thresholds of (-)epicatechin were not found for the concentrations tested which went up to 501ppm. Threshold testing was selected as a starting point to understand how individuals perceive these compounds at sub- and suprathreshold levels. CS and other processing conditions can lead to color compound extraction or must oxidation, resulting in darker colored wines and potentially increasing bitterness intensity. The presence of an association between darker white wine color and bitterness intensity was investigated by having a panel of wine professionals rate the bitterness of color-modified white wine samples. The results did not indicate that wine professionals associate darker white wine color with bitterness. A final study investigated the possibility of differentiating Riesling clones through the analysis of juice monomeric phenolic and tannin profiles. The results did not show significant differences in the monomeric phenolic and tannin profiles among the clones analyzed. However, preliminary sensory results suggest that wine professionals can differentiate among monoclonal Riesling wines. If true, it may be possible to differentiate among Riesling clones through the analysis of other volatile and non-volatile compounds.

Given the rising concerns of herbicide resistance and environmental contamination, investigating ways to eliminate herbicide use in vineyards is warranted. In two Finger Lakes vineyards, cover crops were established annually beneath Riesling vines and compared to a glyphosate-sprayed strip. At one site, natural vegetation, buckwheat, and annual rye grass underneath vines were not found to impact measures of vine growth, yields, or juice characteristics, but did cause differences in wine aroma. At the second site, buckwheat, chicory, and herbicide were maintained beneath vines, with and without irrigation. Using buckwheat did not impact vine growth or yield, but chicory reduced vegetative growth, yields, and titratable acidity in the second year. All treatments were also found to create differences in perceived wine aroma. Further testing of how different under-vine cover crop species affect vine growth and resulting wine aromas in Northeastern Riesling will help provide grape growers with sustainable alternatives to herbicide.

This research study involved the development and validation of an analytical method using solid-phase microextraction (SPME) coupled with gas chromatography - mass spectrometry (GC-MS) for the analysis of 3-alkyl-2-methoxypyrazines in grape juice. These methoxypyrazines are naturally found in grapes and may add to the overall aroma of a wine in low concentrations, but may have a negative affect if the concentrations become too large. This research study will develop and validate a method to track the concentration of the methoxypyrazines as the grapes ripen. A method will also be developed and validated to determine the concentration of methoxypyrazines in Cabernet Sauvignon, and Sauvignon Blanc wines.