The wildfires that swept through Napa Valley in 2020 caused an estimated USD$3.7 billion economic loss to the grape and wine industry. The wines made from smoke-impacted grapes are often described as medicinal, smoky, and possessing a retronasal ashtray character. However, matrix differences among varieties and winemaking styles can impact smoke taint expression as well as the synergistic effects among the volatile phenols responsible for these off-flavors. Serial dilutions of non-impacted and impacted (intentionally smoked post-harvest) wines were used to create wines with differing levels of smoke impact for two wine regions (Napa and Lodi) and styles of Cabernet Sauvignon that were fermented and finished in stainless steel (SS) or subsequently aged in new oak barrels for 12 months. Gas chromatography-mass spectrometry (GC-MS) and liquid chromatography-triple quadrupole mass spectrometry (LC-QqQ-MS) were used to quantify free and total volatile phenols (VPs), and individual bound glycosides, respectively. Descriptive analysis using trained judges and Wine Cuality™ evaluations with wine experts were used to evaluate the sensory characteristics and overall quality of the wines, respectively. Generally, barrel-aged wines saw a decrease in the level of "ashy aftertaste" and smoke-related attributes for both Cabernet Sauvignon wines as compared to their stainless-steel counterparts. Wines with high levels of smoke impact received significantly lower quality ratings (p < 0.05). Interestingly, wines with low levels of smoke-impact consistently received a slightly higher quality rating though not statistically significant when compared to their non-impacted counterparts. These findings contribute to our understanding of grape smoke exposure at different levels of taint and demonstrate the potential value of barrel aging to mitigate overall smoke perception in wine across these taint levels.

Grapevine red blotch disease (GRBD) poses a serious threat to viticulture in the United States. Grapevine red blotch virus (GRBV), a member species of Grablovirus vitis (family Geminiviridae), the causal agent of GRBD, disrupts grapevine physiology and metabolism, thereby interfering with the natural processes of fruit ripening. To date, there is limited knowledge about how grape maturity stages influence the timing of changes in viral load and disease progression. This study elucidates the effect of fruit maturity stages on GRBV accumulation in Vitis vinifera L. cv. Merlot grapevines in a Central Coast vineyard in California. Petioles from six basal leaves at random from previously GRBV-infected vines were collected at pre-véraison, véraison, post-véraison, and harvest stages, across two years (2021 and 2022). The viral copy number was quantified using digital PCR. The study identified significant differences (p < 0.05) in GRBV copy number across different maturity stages in 2021, irrespective of the year of infection. The lowest viral load was observed during the pre-véraison stage, and the highest at harvest, indicating progressive viral accumulation as the grapevines development progressed. In 2022, however, no significant difference in viral load across maturity stages was detected, an outcome attributed to extreme heat spikes coinciding with sampling periods. Our findings highlight the interplay between GRBV accumulation, grape development, and environmental parameters.

Wildfires release volatile phenolic compounds (VPs) that can be absorbed by grapevines, potentially resulting in “smoke taint” in wines. This has emerged as a prominent issue for the global wine industry due to negative impact on wine quality and subsequent financial losses. Since effective vineyard mitigation strategies remain limited, this study evaluated the efficacy of different materials applied to grapes to reduce the absorption of smoke marker compounds under simulated wildfire conditions. Twelve materials were applied to individual Cabernet Sauvignon clusters close to harvest. Treated vines were exposed to intentional smoke using a purpose-built tent. Grapes from treated vines, as well as smoke-exposed and non-exposed controls, were harvested at commercial maturity. The results showed a strong stratification of VPs within the tent and in the grapes. Glycosylation began within hours of smoke exposure, with significant increases in almost all glycosylated compounds within 4 hours compared to non-smoked controls. Some materials reduced VP uptake relative to untreated controls (kaolin, charcoal, and two commercial coating formulations—GM3E and GMB6), whereas others increased the absorption of smoke-derived compounds (Parka and wipe-out). These findings highlight that those protective treatments may have variable and sometimes counterproductive effects on smoke compound uptake.

Volatile phenols (VPs) are present in fresh smoke from wildfires due to thermal degradation of wood lignin and can absorb into grape berry skins where they are rapidly glycosylated. VPs and their glycosides can impact the sensory profile of wines that are characterized by smoky, medicinal aromas and a retro-nasal ashy "aftertaste." Anecdotal evidence indicates 15-20% of consumers cannot distinguish the retro-nasal ashy characteristic of smoke taint. It is difficult to mimic smoke-tainted wine through spiking with related smoke marker compounds due to their complex synergistic interactions with the wine matrix. This study compared smoke-impacted and non-smoke-impacted wines of Cabernet Sauvignon, Malbec, and Syrah varieties made from the same location (Napa and Sonoma). Smoke-impacted grapes were intentionally smoked on drying tables or naturally exposed to smoke during wildfires. The wines were blended through serial dilutions, achieving different levels of smoke impact. The free, total, and bound VPs of all wines were determined by GC-MS and LC-QTOF-MS, respectively. Wines were sensorially evaluated by 62 wine experts and 58 regular wine consumers separately; using a series of hedonic, Just-About-Right, and Check-All-That-Apply questions. Correspondence analysis determined that different levels of smoke impact were detected differently by wine experts and consumers. Experts could distinguish smoke impact at lower levels, as determined by VP analysis, and compared to consumers who were generally only able to distinguish smoke-impacted wines at higher levels. Further difference testing with an additional group of wine consumers, saw an increase in the sensitivity towards smoke when consumers were trained to identify/recognize the ashy attribute. PRACTICAL APPLICATIONS: This research provides winemakers with valuable insights into how wildfire smoke impacts wine flavor and the levels at which both expert and non-expert consumers can detect smoke taint. By understanding these sensory thresholds, wineries can make informed decisions on whether and how to treat smoke-affected wines-particularly through blending strategies. This enables them to manage quality in smoke-exposed vintages and transform wines that might otherwise be unsellable into acceptable, marketable products.

Smoke taint in wine has become a critical issue in the wine industry due to its significant negative impact on wine quality. Data-driven approaches including univariate analysis and predictive modeling are applied to a data set containing concentrations of 20 VOCs in 48 grape samples and 56 corresponding wine samples with a taster-evaluated smoke taint index. The resulting models for predicting the smoke taint index of wines are highly predictive when using as inputs VOC concentrations after log conversion in both grapes and wines (Pearson Correlation Coefficient PCC = 0.82; R2 = 0.68) and less so when only grape VOCs are used (Pearson Correlation Coefficient PCC = 0.76; R2 = 0.56), and the classification models also show the capacity for detecting smoke-tainted wines using both wine and grape VOC concentrations (Recall = 0.76; Precision = 0.92; F1 = 0.82) or using only grape VOC concentrations (Recall = 0.74; Precision = 0.92; F1 = 0.80). The performance of the predictive model shows the possibility of predicting the smoke taint index of the wine and grape samples before fermentation. The corresponding code of data analysis and predictive modeling of smoke taint in wine is available in the Github repository (https://github.com/IBPA/smoke_taint_prediction).

The majority of rose ' wines are bottled in clear bottles as color is an important factor in consumer preference. Post-bottling wine can be exposed to UV-visible light and temperature fluctuations resulting in quality degradation. This study investigated the impact of bottle color (flint and antique green), light exposure (darkness, LED and fluorescent bulb), and temperature (12 degrees C and 22 degrees C) on rose ' wine quality using a full factorial design with three different wines (Grenache, Pinot noir and Zinfandel). The impact on chemical composition, color, phenolics and aromatics was determined. Projective mapping was carried out for sensorial analysis. Changes in the aromatics, color and phenolic composition were detectable after three months and more noticeable after six months of storage. Overall, all variables studied impacted rose ' wine characteristics significantly. However, higher temperature in combination with clear glass bottles under fluorescent light were the most detrimental conditions.

This study is an investigation of the impact of volatile phenols (VPs) released from burning wood during wildfires on grape composition and the resulting wines. Baseline levels of VPs in grapes and sensory differences between smoke-impacted wines and non-smoke-impacted wines were determined. The differences were related to different levels of smoke taint marker compounds in different wine matrices, using modified descriptive analysis (DA), multivariate statistics, gas chromatography mass spectrometry (GC-MS) and liquid chromatography-triple quadrupole tandem mass spectrometry (LC-QqQ-MS) of the free and total VPs, and individual bound glycosides, respectively. Across two DA panels, Cabernet Sauvignon, Cabernet Franc, Petite Verdot, Merlot, Syrah, Malbec, and Zinfandel wines made from grape originating from different areas in California were evaluated. The results show sensory differences between highly smoke-impacted and non-impacted wines with wines made from highly smoke-impacted grapes characterized as smoky, barbeque, medicinal, and having a retro-nasal ashtray character. Low smoke-impact wines based on free and total VP concentrations were not significantly different from the non-impacted wines when rated through descriptive analysis. The amount of smoke exposure was the largest contributor to smoke impact determined by sensory evaluation, but the different wine matrices from different locations and varietals also played an important role in determining the level of perceived smoke impact. The results of this study will contribute to our understanding of smoke impact and how it influences wine characteristics by relating smoke marker indicator compounds to wine sensory attributes.

BACKGROUND: Grapevine red blotch virus (GRBV) is a recently discovered virus and a major concern for the wine industry. Prior research indicated that GRBV delays grape ripening by reducing degrees Brix and anthocyanin concentrations in grapes from infected vines, resulting in higher ethanol concentrations in wines made from healthy fruit compared to diseased vines, which have an impact on sensory properties. In this study, infected fruit (Vitis vinifera L. Merlot) was sequentially harvested (in 2016 and 2017) and chaptalized (in 2017) to ameliorate the impact of GRBV on grape and final wine composition. RESULTS: Chemical parameters including phenolic and volatile profiles of grapes and their subsequent wines were measured. Sensory properties were determined by descriptive analyses. Results demonstrated that GRBV decreased sugar accumulation and anthocyanin synthesis in grapes. Wines from GRBV grapes harvested at later ripening stage produced wines that were more similar chemically and sensorially to wines made from healthy fruit than to wines made from GRBV fruit harvested earlier. CONCLUSION: A longer hang time of GRBV grapes is a potential strategy to mitigate the impacts of GRBV. However, chaptalization of diseased fruit must was inefficient at increasing similarities to wines made from healthy fruit. (c) 2023 Society of Chemical Industry.

Background and goals Grapevine red blotch disease (GRBD) causes a delay in ripening events in grapes, subsequently decreasing sugar accumulation, inhibiting anthocyanin biosynthesis, and affecting cell wall metabolism. Phenolic extractability is reduced in wine made from GRBD fruit, which can be slightly improved by extending the ripening period of GRBD grapes. However, further enological techniques that increase phenolic concentrations in wine or facilitate cell wall degradation have not been investigated in GRBD fruit. Methods and key findings Vitis vinifera L. cv. Merlot grapevines with GRBD symptoms were harvested twice, two weeks apart, in 2019 and 2020. Pectolytic enzyme addition and extended maceration were performed on the second harvest of GRBD fruit to improve phenolic extraction during fermentation. Phenolic concentrations, volatile profiles, and sensory characteristics were analyzed for all wine produced. Seasonal factors and harvest time were found to affect the phenolic extractability, chemical composition, and sensory characteristics of wine made with GRBD fruit. Compared to control wine, extended maceration of wine made with GRBD fruit largely did not improve chemical composition or sensory characteristics, and on ly minor increases of tannin concentrations were found during fermentation. Wine composition and sensory properties primarily depended on vintage and harvest time, rather than enological technique applied. Conclusions and significance A delayed harvest of diseased fruit had a greater effect on phenolic composition in the wines than did the analyzed enological techniques, consistent with previous findings. However, this finding depends on variations across different seasons.

When grapes are exposed to wildfire smoke, certain smoke-related volatile phenols (VPs) can be absorbed into the fruit, where they can be then converted into volatile-phenol (VP) glycosides through glycosylation. These volatile-phenol glycosides can be particularly problematic from a winemaking standpoint as they can be hydrolyzed, releasing volatile phenols, which can contribute to smoke-related off-flavors. Current methods for quantitating these volatile-phenol glycosides present several challenges, including the requirement of expensive capital equipment, limited accuracy due to the molecular complexity of the glycosides, and the utilization of harsh reagents. To address these challenges, we proposed an enzymatic hydrolysis method enabled by a tailored enzyme cocktail of novel glycosidases discovered through genome mining, and the generated VPs from VP glycosides can be quantitated by gas chromatography-mass spectrometry (GC-MS). The enzyme cocktails displayed high activities and a broad substrate scope when using commercially available VP glycosides as the substrates for testing. When evaluated in an industrially relevant matrix of Cabernet Sauvignon wine and grapes, this enzymatic cocktail consistently achieved a comparable efficacy of acid hydrolysis. The proposed method offers a simple, safe, and affordable option for smoke taint analysis.

Introduction:Overhead photoselective shade films installed in vineyards improve berry composition in hot grape-growing regions. The aim of the study was to evaluate the flavonoid and aroma profiles and composition of wines from Cabernet Sauvignon grapes (Vitis vinifera L.) treated with partial solar radiation exclusion.Methods:Experimental design consisted in a randomized experiment with four shade films (D1, D3, D4, D5) with differing solar radiation spectra transmittance and compared to an uncovered control (C0) performed over two seasons (2021 and 2022) in Oakville (CA, USA). Berries were collected by hand at harvest and individual vinifications for each treatment and season were conducted in triplicates. Then, wine chemical composition, flavonoid and aromatic profiles were analyzed.Results:The wines from D4 treatment had greater color intensity and total phenolic index due to co-pigmentation with anthocyanins. Shade film wines D5 and D1 from the 2020 vintage demonstrated increased total anthocyanins in the hotter of the two experimental years. In 2021, reduced cluster temperatures optimized total anthocyanins in D4 wines. Reduced cluster temperatures modulated anthocyanin acylation, methylation and hydroxylation in shade film wines. Volatile aroma composition was analyzed using gas chromatography mass spectroscopy (GCMS) and D4 wines exhibited a more fruity and pleasant aroma profile than C0 wines.Discussion:Results provided evidence that partial solar radiation exclusion in the vineyard using overhead shade films directly improved flavonoid and aroma profiles of resultant wines under hot vintage conditions, providing a tool for combatting air temperatures and warmer growing conditions associated with climate change.

BACKGROUNDGrapevine red blotch virus (GRBV) is the causal agent of grapevine red blotch disease and is known to delay grape ripening. However, grape cell-wall modifications during GRBV infection are largely unknown, even though the cell wall plays a large role in pathogenicity, viral interactions with host plants, and phenolic extractability during winemaking. Understanding the impact of GRBV infection on cell-wall metabolism is important for the development of potential mitigations strategies. In this study, high-throughput transcriptome sequencing was conducted on Vitis vinifera L. 'Merlot' grapes during ripening. The cell-wall composition, phenolic content, and phenolic extractability at two different commercial harvest points were also determined. RESULTSLog fold changes indicated a strong induction in diseased grapes at harvest of several transcripts involved in cell-wall solubilization and degradation. However, these observations did not translate to changes in cell-wall composition at either harvest point in diseased grapes, potentially suggesting post-transcriptional regulation. Moderate induction of pectin methylesterase inhibitor transcripts and transcripts associated with pathogenesis-related proteins coincided with increases in pectin and soluble proteins in cell walls of diseased grapes at harvest. Both pectin and pathogenesis-related proteins are known to retain phenolic compounds during winemaking. CONCLUSIONOur study corroborates this finding when the percentage extractability of flavonols in wines was significantly lower when made from GRBV-infected fruit. These results suggest GRBV alters the grape cell walls, consequently decreasing phenolic extraction during winemaking. (c) 2023 Society of Chemical Industry.

Grapevine red blotch virus (GRBV) is a recently identified virus. Previous research indicates primarily a substantial impact on berry ripening in all varieties studied. The current study analyzed grapes' primary and secondary metabolism across grapevine genotypes and seasons to reveal both conserved and variable impacts to GRBV infection. Vitis vinifera cv. Cabernet Sauvignon (CS) grapevines grafted on two different rootstocks (110R and 420A) were analyzed in 2016 and 2017. Metabolite profiling revealed a considerable impact on amino acid and malate acid levels, volatile aroma compounds derived from the lipoxygenase pathway, and anthocyanins synthesized in the phenylpropanoid pathway. Conserved transcriptional responses to GRBV showed induction of auxin-mediated pathways and photosynthesis with inhibition of transcription and translation processes mainly at harvest. There was an induction of plant-pathogen interactions at pre-veraison, for all genotypes and seasons, except for CS 110R in 2017. Lastly, differential co-expression analysis revealed a transcriptional shift from metabolic synthesis and energy metabolism to transcription and translation processes associated with a virus-induced gene silencing transcript. This plant-derived defense response transcript was only significantly upregulated at veraison for all genotypes and seasons, suggesting a phenological association with disease expression and plant immune responses.

The composition of skin cell wall material from Pinot noir and Cabernet Sauvignon grape berries from four different regions in California was investigated to determine relationships between cell wall composition and phenolic extractability observed under winemaking conditions. Multiple vineyards (sites) per region were studied. Cell wall composition analysis included determining total soluble sugars , proteins , noncellulosic glucose , cellulose , lignin , lipids , total polyphenolic content , soluble polysaccharides , and uronic acid , as well as isolation efficiency. Results indicated that cell wall material (CWM) composition is mainly site-specific , with some effect due to variety and little to no effect from the growing region. Grape phenolics analyzed included monomeric flavan-3-ols , antho-cyanins , polymeric phenols , and polymeric pigments and could be used to distinguish between varieties. Grapes grown in the same region exhibited similar phenolic extractability , indicating a significant effect of the growing area , as well as a synergistic effect between CWM composition and grape phenolics. CWM composition analysis indicated that demethylation of pectin favored the release of phenolics , while lignin content correlated negatively with the phenolics extracted. Proteins showed a negative correlation with polymeric phenols , whereas no correlation was found with polymeric pigments. Anthocyanin extractability was highly affected by its content within grape skins, more so than other phenolics that are present in both the skins and seeds.

White wine fermentations are typically performed in an entirely batchwise manner, with yeast nutrients only added at the beginning of fermentation. This leads to slow (2+ weeks) fermentation cycle times, with large capital expenditures required to increase winery processing capacity. Prior attempts to speed fermentations via increasing temperature have resulted in unpalatable wine, and continuous fermentation processing is uneconomical and impractical in the winery setting. In this work, we measured yeast nutrient consumption as a function of fermentation progression at the 300 mL scale, and from this derived an equation to optimize yeast nutrient concentration as a function of fermentation progression. These findings were applied at the pilot scale in 150 L fermentors, which resulted in a 60% cycle time reduction versus “best practices” control fermentations. The resultant wines were compared via GC-MS as well as by a trained sensory panel. Organoleptic analysis found statistically significant, but overall, small differences in sensory characteristics between the control and process intensified wines. This intensified fermentation process shows great promise for fermented beverage producers wishing to maximize equipment utilization and debottleneck wineries or other beverage fermentation facilities.

The importance of grape harvesting procedures is discussed in the context of 50 years of development and application of mechanical harvesters. Lower costs of mechanical harvesting on larger vineyards need to be weighed against inclusion of unwanted material and risks of unwanted oxidation. A summary of literature findings is presented both for white and red wines. In many trials similar quality wines have been produced from both hand-picking and mechanical harvesting of grapes. The aroma compounds most affected by harvesting decisions, particularly antioxidant additions at harvest with white wines, are C6 compounds and the varietal thiols. Options to improve grape composition with mechanical harvesting include the use of optical sorting systems.

There is an increase in the levels of volatile phenols in wine made with smoke-impacted grapes. These compounds are present in wood smoke resulting from the pyrolysis (thermal decomposition) of lignin and at high levels give overpowering smoky and ashy characters to a wine. This research aimed to compare all the suggested wine mitigation strategies that evolved from prior research using smoke-impacted grapes under identical winemaking conditions except for the parameter under investigation. Cabernet Sauvignon grapes were received from three areas with varying amounts of smoke exposure in Northern California. Gas chromatography combined with mass spectrometry (GC-MS) and descriptive analyses were performed to correlate the volatile phenol composition to smoke taint characteristics. The winemaking variables investigated were the use of different fermentation yeasts, oak additions, and fermentation temperatures. Among other attributes, smokiness and ashy aftertaste were significantly different among the wines, showing a clear difference between the wines made from smoke-impacted fruit and the control wines made from non-impacted fruit. Findings indicate that mitigation strategies during red wine fermentation have a limited impact on the extraction of smoke-taint markers and the expression of smoke-taint sensory characteristics.

Vineyard exposure to wildfire smoke can taint grapes and wine. To understand the impact of this taint, it is imperative that the analytical methods used are accurate and precise. This study compared the variance across nine commercial and research laboratories following quantitative analysis of the same set of smoke-tainted wines. In parallel, correlations between the interlaboratory consensus values for smoke-taint markers and sensory analyses of the same smoke-tainted wines were evaluated. For free guaiacol, the mean accuracy was 94 ± 11% in model wine, while the free cresols and 4-methylguaiacol showed a negative bias and/or decreased precision relative to guaiacol. Similar trends were observed in smoke-tainted wines, with the cresols and glycosidically bound markers demonstrating high variance. Collectively, the interlaboratory results show that data from a single laboratory can be used quantitatively to understand smoke-taint. Results from different laboratories, however, should not be directly compared due to the high variance between study participants. Correlations between consensus compositional data and sensory evaluations suggest the risk of perceivable smoke-taint can be predicted from free cresol concentrations, overcoming limitations associated with the occurrence of some volatile phenols, guaiacol in particular, as natural constituents of some grape cultivars and of the oak used for barrel maturation.

Grapevine red blotch virus (GRBV) negatively affects the composition of grapevine ( Vitis vinifera , L.) berries by reducing total soluble solids and anthocyanins, leading to economic losses for producers. Negative effects of GRBV were suspected to be due to impeded carbon translocation from leaves to fruit which limit sugar and flavonoid accumulation in berries. A two-year trial was conducted to determine whether source-sink manipulation on GRBV(+) Cabernet Sauvignon plants may affect non-structural carbohydrate partitioning and possibly mitigate the effects of GRBV. The source:sink ratio was altered by removing some clusters without altering leaf area in a factorial arrangement of healthy plants that did not have the virus (GRBV (-)) and plants having GRBV (GRBV (+)). Effects of cluster thinning and virus status on leaf and shoot non-structural carbohydrates, plant water status, leaf gas exchange, berry primary and secondary metabolites, and yield components were measured. Total non-structural carbohydrates in leaves began to accumulate around véraison. In shoot xylem sap, GRBV(-) plants had greater concentration in total non-structural carbohydrates than GRBV(+) plants. The presence of disease improved plant water status increasing the stem water potential and increasing berry mass. However, juice total soluble solids were consistently lower in GRBV(+) plants despite altering the source: sink by 3× with cluster removal. Likewise, GRBV(+) plants produced berries with lower anthocyanin content at harvest regardless of CT in both years. Our results provided fundamental evidence that impeded carbohydrate translocation imposed by GRBV is too great to overcome by cluster thinning and will result in inadequate fruit composition regardless of crop level imposed.