Measuring Grape Smoke Taint Protection

Smoke taint has become a recurring issue since 2008, and one that has led to crop losses as well as legal disputes between growers and processors. With the expectation that the intensity and frequency of wildfires will continue to increase in California and impact the winegrape producing regions, it is important to investigate potential ways to mitigate the impact of grape smoke exposure. There are now a number of products and processes available in the market to treat the wine, but also materials to prevent or limit the impact of smoke exposure by applying a protective material to the grapes. As these are new problems and new remedies, it is important to have a means to test the effectiveness of such treatments. We created a simple standardized evaluation of grape protection treatments in order to compare their relative effectiveness.

Grape smoke exposure effects: Determining the compounds that cause smoke impacts in wine

The overall goal of this work is to identify those compounds from smoke that cause negative impacts to wine quality. We are taking a different approach than other research on this topic. In short, we are creating label smoke compounds by growing barley (our fuel source) in a 13CO2 environment. We are then able to track the labeled carbon in the smoke, grapes and wine using NMR, which is very sensitive to 13C.

The accomplishments for the project for the 6 months has been to design the chambers needed to grow barley in elevated CO2 environments (Objective 1A). Our first barley lots (0-4) were/are being run using regular CO2 due to the expense of isotopic 13CO2. Once we have determined the optimal CO2 levels in the chambers we will switch to 13CO2. Development of the chambers included not only how to increase carbon fixation of the 13C in the plant, but determined how to measure the isotopic CO2 and other necessary plant measurements. We are on track to have 13C labeled barley to burn and produce 13C smoke for the 2020 vintage.

Identification of smoke odorants by gas chromatography/olfactometry and assessment of smoke odorants in grapes and wine

Smoke taint has become a significant concern for the wine industry, particularly in Southern Oregon and California, partly due to climate change. Smoke taint is an off-aroma describing the wine with smoky, medicinal, and ashy characters, and this unpleasant taint is caused by grapes or grapevine exposed to bushfire smoke before. Wine made from smoke-tainted grapes is often characterized by smoky, burnt, burnt rubber, ashy, smoked salmon, smoked meats, salami, leather, disinfectant/hospital, medicinal, dusty, and earthy aromas. Guaiacol, 4-methylguaiacol, and syringol have smoky odors with low sensory thresholds, and these compounds are likely to contribute to the overall smoke flavor.

When guaiacol and other smoke-related compounds are absorbed by the grapevine, the grapevine will convert them to the corresponding glycosides or other bound forms. These glycosides as well as the bound form precursors do not exhibit aroma themselves, but can be converted back to the odorants during winemaking and wine aging process. Grape maturity, grape varieties, and bottle aging can all influence the intensity of smoke taint in wines.

Smoke taint precursors, including glycosides, can persist in the wine and directly affect flavor perception during consumption. Guaiacol β-D-glucoside and m-cresol β-D-glucoside in model wine were found to give rise to a smoky or ashy flavor in-mouth, due to the release of respective free volatiles in-mouth. It has been confirmed that the enzymes present in human saliva can release the volatile smoke compounds from their glycoconjugates even under low pH and elevated ethanol conditions. Smoke taints in grapes and their conversion during winemaking, and wine aging are very complex, the mechanisms of transformation need to be thoroughly investigated to mitigate the issue.

Although guaiacol, 4-methylguaiacol, 4-ethylguaiacol, 4-ethylphenol, eugenol, and furfural are related to bushfire smoke, but not all of them are directly generated from smoke, some of them can naturally exist in grapes or extracted from the wine barrel. These compounds are essential contributors to wine flavor at low concentrations.
Our initial experiments were designed to extract the smoky chemicals from wine. Complementary analytical methods have been evaluated. The results showed that smoky odorants can be obtained from wine using different methods. Further investigations were under progress to identify the smoky odorants.

Investigation of different winemaking protocols to mitigate smoke taint character in wine

Research regarding smoke taint has mostly been undertaken in Australia with a focus on vine susceptibility, potential mitigation actions during winemaking to limit smoke taint expression and potential ways to remove smoke taint in the final wines. Thorough review of published smoke taint research indicated large gaps in knowledge and inconsistent results. The objective of the research project was to compare all the suggested wine protocols that evolved from the current literature using one batch of smoke impacted grapes under identical winemaking conditions except for the parameter under investigation. Results from this study will enable to us to better advice the wine industry during future smoke events. Results from this study will enable us to better advice the wine industry during future smoke events. SPME-GC-MS and UPLC-Q-TOF-MS methods employing stable isotope dilution methodology (SID) have been implemented. Cabernet Sauvignon grapes were received from three different areas with varied amounts of smoke exposure (Oakville, Alexander Valley, and Silverado Trail AVA’s) in Northern California. Gas chromatography mass spectrometry (GC-MS) and sensory analysis were performed in order to correlate wine 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 found to be significantly different among the wines, showing a clear difference between the wines that were made from smoke impacted fruit and the control wines that were made from non-impacted fruit. One yeast showed a significant effect by highlighting the fruitiness in the wines and reducing the ashy aftertaste. Different oak additions were not successful in masking the impact of the smoke. Similarly, different fermentation temperatures did not have a significant impact on smoke expression in the resulting wines. Findings indicate that mitigation strategies during red wine fermentation have a limited impact on the extraction of smoke taint markers as well as the expression of smoke taint sensory characteristics.

Effect of grapevine red blotch disease (GRBD) on flavor and flavor precursor formation in the grape and on wine quality

Two field experiments were established to investigate the effects of grapevine red blotch disease (GRBD) on flavor and flavor precursor formation in the grape berry and on resulting wine quality. The two objectives of the overall study were to 1) investigate the effect of GRBD on grape berry development with a specific focus on flavor and flavor precursor formation; and to 2) investigate the effect of GRBD on wine quality. Both experiments were located in the same vineyard located near the town of Jacksonville, OR. In both experiments, data vines were identified by visual disease symptoms (or lack thereof), and disease status was confirmed using PCR-based assays in Dr. Achala KC’s laboratory at SOREC.

To evaluate the response of flavor and flavor precursor compounds to GRBV infection during berry development (objective 1), clusters from GRBV+ and GRBV- vines were sampled weekly beginning from just before veraison through to commercial harvest. Vine water status, berry growth, and development were also monitored in those plots subjected to different irrigation treatments. Vine water status was monitored by measurements of midday stem water potential (Ψstem). Results showed that there was no significant interaction between irrigation treatment and disease status on Ψstem. However, there were significant effects of irrigation treatment and disease status on Ψstem independently. Berry size (fresh weight; FW) was consistently higher in GRBV+ vines, significant differences in TSS between GRBV+ and GRBV- vines were observed. There were no significant differences in berry pH between vines of different disease status over the entire course of berry development. Berry titratable acidity (TA; g L-1) were lower in GRBV+ fruit. These responses were only observed after veraison, but they are not as consistent. Flavor and flavor precursor analysis in the grapes is underway.

To evaluate the response of wine quality to GRBV infection (Objective 2), replicate wines were produced from field plots under the supervision of Dr. James Osborne using a standard protocol. Wines were analyzed for volatile aroma compounds using  different techniques including headspace-GC-FID, solid-phase microextraction gas chromatography-mass spectrometry (SPME-GC-MS) and stir bar sorptive extraction-gas chromatography-mass spectrometry method (SBSE-GC-MS), stale-isotope compounds were used as internal standards for accurate analysis. Monomeric anthocyanin and total phenolic contents in wine were also analyzed. Results showed that the RB negative wines under irrigation condition have the highest level of monomeric anthocyanin than other three groups. Total phenolic content varies in wines with different irrigation conditions. Fermentation derived aroma compounds did not show any difference between RB+ and RB-, nor free form grape-derived aroma compounds. Since the free form of grape derived aroma compounds only exist in a small portion, and the majority of these compounds exist in the bound form, analysis is underway for the bound form of volatile flavor compounds in the wine.

Investigation of different amelioration techniques to remove smoke taint character from wine

Research regarding smoke taint has mostly been undertaken in Australia with a focus on vine susceptibility, potential mitigation actions during winemaking to limit smoke taint expression and potential ways to remove smoke taint in the final wines. Thorough review of published smoke taint research indicated large gaps in knowledge and inconsistent results. The objective of the proposed research is to compare all the suggested amelioration techniques using the same wine and follow the changes in free and bound smoke taint compounds before and after treatment as well as with wine aging up to one year. Results from this study will enable us to better advice the wine industry during future smoke events. SPME-GC-MS and UPLC-Q-TOF-MS methods employing stable isotope dilution methodology (SID) have been implemented. Smoke-exposed Cabernet Sauvignon wine was made from Oakville Experimental Station fruit. Wines were treated for one to six weeks with a range of different enzymes (Lafazym AROM, Lyvarome A5, Sumizyme BGA and Zimarom) at two different addition levels (2 and 4 g/hL). Control and enzyme-treated wines (those showing elevated volatile phenols) will be treated with activated charcoal fining, reverse osmosis, Conetech smoke removal technology and molecular imprinted polymers. Those treatments showing a significant decrease in free and/or bound volatile phenols will be evaluated by descriptive analysis.

Managing Protection of Varietal Aromas From Wine Oxidation

In order to investigate the reactions of quinones with unknown nucleophiles to further understand how quinones react in wine. The quinone reaction products are investigated by Q-TOF using 13C6 labels. Since the labeled compound is expensive, we used the unlabeled catechol (12C6) first to determine the levels of 13C6 labels we needed, the incubation time, and the Q-TOF method development. We have set up a list of the products from quinone with the known nucleophiles and optimized the analysis method to maximize the numbers of the detection of these known products. Considering the total amount of catechols, such as caffeic acid, catechin, cyanidin, are around 2g/L for red wines and 0.5g/L for white wines and the expecting detection limit of the product is around 2 mg/L, 0.1g/L quinone was added to wines and the level was confirmed by the trials. The incubation time was also tested and finally chosen as 2 hours.

Chiral Terpenes – Quantitation, Threshold Determination and Sensory Impact on Aromatic White Wines

The specific accomplishment of the last year for this project was the development of a quantitative method using MDGC to measure chiral terpenes in white wine. Two hundred and three white wine samples, Pinot Gris and Riesling with diverse residual sugars had been already collected from different places of origin all over the world. Wines were donated from top wine companies from New Zealand, New York, Australia, Germany, Oregon, Washington, France, to name a few. Fifteen chiral mono-terpene compounds were collected from head space solid phase micro-extraction coupled with multidimensional GC-MS with stable dilution isotope quantification analysis. Results for the Pinot Gris wines are presented in this report. In short here were difference sin chiral terpene content between the wines. Additional differentiation was established for place of origin of Pinot Gris wines based on chiral terpene content.

Understanding Pinot Noir Grape and Wine Aroma Composition as a result of changes in Vine Balance, year 1 of a 3

Vine balance is important in determining fruit and wine composition. Excessive canopy density is known to produce unbalanced musts, resulting in poor wine quality. In Oregon, crop thinning is normally conducted between fruit set and lag phase to increase the leaf area: fruit weight ratio in order to prevent over cropping, as well as to improve fruit size and composition. Earlier studies have shown that cluster thinning reduces fruit yield and increases the berry weight, soluble solids, and color of table grapes. However, the impacts of the timing and severity of cluster thinning on subsequent berry growth and fruit flavor composition has not been widely investigated. The main objective of the present study was to evaluate such effects in association with grape and wine aroma composition in Pinot noir grapes and wine. Preliminary results indicated that crop thinning had very limited impact on the grape major volatile composition analyzed in 2011 and 2012. However, the composition of other minor and important compounds, such as methoxypyrizes, are still under investigation.

Judging Wine Quality: Do We Need Experts, Consumers or Trained Panelists?

The overall objective is to determine if quality can be reliably evaluated by wine consumers, wine aficionados and/or wine experts and what their quality scores actually mean relative to the intensities of the sensory attributes we get from trained panels, and the liking scores we get from wine consumers. To choose wines with different quality levels we used the judging scores assigned to 27 Cabernet sauvignon wines in the 2012 California State fair judging competition.

At this competition Cabernet wines are divided into 9 regions. Within each region we picked the wine with the highest score (usually a gold medal wines), the wine with the lowest score (a wine that did not medal) and then a wine with a score as close to the mean between the highest and lowest score. The 15 descriptive analysis panelists (10 males, 22-72 years old, average age 37 yrs, median 31 yrs, standard deviation 17 yrs) were recruited from the students, staff and faculty of the Departments of Viticulture & Technology, Food Science & Technology, and Aerospace Engineering. They participated in 6 1-hr training sessions to collect, generate and obtain consensus on 21 aroma, 3 taste and 3 mouthfeel attributes. Their evaluation of the wines, in triplicate will be complete on 2/7/13. The consumer hedonic evaluation, using the 9-point hedonic scale has been scheduled for February 2, 2013 – we are aiming to have about 192 participants and each participant would evaluate 6 wines. Thus each of the 27 wines would be evaluated by 42 or 43 consumers.