Tropical Fruit Aroma in Wine

AVF Proj. ID: 2479 / /Cat.:
Primary Investigator(s): Elizabeth Tomasinoby

Summary The overall goal of this project is to produce Chardonnay wines with increased tropical fruit aroma perception. In a previous study developed by Dr. Elizabeth Tomasino’s research group, we found that wines with higher concentrations of fermentation esters and volatile thiols imparted more intense tropical fruit aroma nuances. Therefore, in this projectspecific winemaking processes (skin contact, β-lyase addition, and two fermentation gradient temperature regimes) were performed with the intent to either increase or decrease these aromas in the wine. The first two processes (skin contact and β-lyase addition) are known for increasing volatile thiol concentrations in wine. The latter (fermentation temperature) is expected to increase thiol concentrations and preserve fermentation esters. The accomplishments for the project for the 2022 year include sensory analysis of wines that were scaled up, including consumer liking and emotional response. Basic wine chemical analysis and ester analysis was performed on all wines. Samples have been prepped for thiol analysis and PI has worked towards synthesizing thiol precursors, as purchasing standards has been challenging. While we cannot yet link the thiol and ester concentrations to the aromas noted in the wines in this project, wine consumers have positive emotional responses to the control, skin contact +fermentation gradient and fermentation gradient wines. The wines with only skin contact were associated with very negative emotions. Additionally, the three wines with positive aromas were described with different tropical fruit descriptors.

Revisiting Tartrate Stability

AVF Proj. ID: 2475 / /Cat.: ,
Primary Investigator(s): Andrew Waterhouse, Ph.D.by

Despite the claim in the initial proposal that there were no known barriers to completing this project in a timely fashion, the world conspired to make that a lie. Between March of 2020 and the end of October, on campus research at UC Davis was restricted to time sensitive research activities (“Phase 2 activities”) and was expanded to include some research that needed on site access on 30th October (“Phase 2x”). Restrictions continue regarding number of personnel, as do guidelines for high-risk employees. This was again changed when the state of California entered a second lockdown between Dec 22 to Jan 25 of 2021. It is anticipated that there is the potential for additional restrictions in on-campus access as the virus status changes.

In April, when it became clear that these restrictions would be a serious barrier, the project investigators purchased, and installed, equipment required for this project in an off-site location to allow the work to take place outside of these restrictions. This process was slowed by all the now familiar issues of operating in a COVID world. This offsite location now can run all the tests described in the original project proposal Table 3 (below) and will continue to be the research location until COVID restrictions are removed completely (UC Davis “Phase 4”)

As of December 2020, the equipment was installed and functional. The researchers are in the process of validating the equipment and proceeding on the original project’s Goal 1:

Goal 1: Standard precision tests will be done by repeated analysis with specific variations in sample, subsample, day, equipment and/or analyst to provide information on method repeatability and replicability. If adequate collaborators can be found, a reproducibility value will also be generated; if not, standard multiples of repeatability can be used as a working estimate of reproducibility.

The adjustment to the original timeline in response to this situation shows a delay of about eight months. We do not foresee additional delays due to COVID related restrictions other than any normal disruptions in deliveries or access.

One potential advantage of the new set up is the ability to increase the output of experimentation over the next several months and make up for loss of time. If that proves the case, the researchers will move onto the proposed future goals proposed in the original proposal.

Goal 4: Correlate the analytical responses of selected non-redundant tests to specific “risk” storage or transportation conditions (such as short time-extreme cold or long time- mild cold storage, with or without other extenuating conditions) which could impact the “potassium bitartrate stability” of the wines. This will determine the analytical method’s predictive abilities.

Measuring Grape Smoke Taint Protection

AVF Proj. ID: 2343 / /Cat.: ,
Primary Investigator(s): Andrew Waterhouse, Ph.D. and Anita Oberholster, Ph.D.by

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

AVF Proj. ID: 2360 / /Cat.: ,
Primary Investigator(s): Elizabeth Tomasino, Ph.D.by

The goal of this project is to determine the volatile chemicals in smoke that affect the flavor and aroma of wine and wine grapes for Pinot noir and Chardonnay. To differentiate chemicals derived from smoke from ambient grape or wine compounds, a fuel source, barley, was chemically “tagged” using 13CO2. As 13CO2 is assimilated by the barley, it is distributed throughout the plant and its chemical components, including the precursor smoke material, such as lignin. By identifying the major components from smoke, future studies may be able to better prevent off-flavors caused by smoke from nearby wildfires. More immediate conclusions may even begin to identify thresholds when crops are exposed to smoke to the point of sensory perception prior to harvest or fermentation.

To achieve these goals, in this year we have:

  • Implemented 13CO2 incubation cages for growing isotopically labelled barley (Figure 1)
  • Tested and concluded ideal practical conditions to maximize growth of 13C-labelled barley
  • Grew over 2 kg (dry weight!) 13C-labelled barley from January through September
  • Adjusted protocols to account for Covid-19 lockdowns and personnel distancing as outlined by state and university policies, continuing the project with minimal interruption
  • Begun processing and milling barley samples to determine lignin, carbohydrate, and dissolved composition through chemical methods, and 13C assimilation via isotope ratio mass spectrometry
  • Designed and constructed smokers and smoke tents for smoking wine grapes using chemically labelled barley as a fuel source (Figure 2)
  • Designed methodology to recreate high density smoke conditions while balancing cost[1]effectiveness of administering labelled smoke while ensuring the viability of the wine
  • Exposed over 20 kg Chardonnay and 20 kg Pinot noir grape clusters to labelled smoke, consistently holding smoke labelled smoke density >20 mg/m3 over the course of 3 days in October (Figure 3)
  • Made wine from grapes exposed to 13C-labelled smoke (Figures 4 and 5)

Preliminary aroma and flavor of smoke-exposed wine show a strong incorporation of chemicals associated heavily smoked grapes, with a marked difference between the grapes exposed to smoke in the tents and the control grapes that were exposed to smoke during the wildfire events in Oregon in September. Moreover, we expect to be able to differentiate the chemicals’ origins based on the NMR experiments and confirmed by GC- or LC-MS in 2021.

Identification of Smoke Odorants by Gas Chromatography/Olfactometry and Assessment of Smoke Odorants in Grapes and Wine

AVF Proj. ID: 2312 / /Cat.: ,
Primary Investigator(s): Michael Qianby

There are two primary objectives for this funding cycle. One is to build reliable analytic methods for smoke compounds quantification, and another one is to build a database for smoke assessment. We developed a headspace solid-phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS) method and a stir bar sorptive extraction-gas chromatography-mass spectrometry (SBSE-GC-MS) method to analyze 13 smoke-related compounds. When stable-isotope internal standards are used, the HS-SPME-GC-MS is fast and reliable and can analyze smoke-related compounds in different wines. However, the stable[1]isotope internal standards are not commercially available for all 13 smoke-related compounds. In comparison, the SBSE-GC-MS method is more sensitive and less dependent on the wine matrix.

To respond industry’s smoke exposure concern, we developed a rapid method based on the SPME-GC-MS technique with isotope compounds as the internal standards. We can analyze guaiacol, 4-methylquaiacol, 4-ethylguaiacol, o-cresol, m-cresol, and p-cresol, 4-ethylphenol in 30 min. Our analytical results were verified with a certified commercial lab.

Using this rapid analytical method, we analyzed over 370 smoked exposed red wines and 90 smoke-exposed white wines (including rose wine). A standard was run every ten samples to verify recovery and instrument performance, and a duplicate sample was analyzed every 20 samples. Both free phenols and total phenols (after acid hydrolysis, pH 1, 100C/4h) were analyzed for all the samples. Out of the 370 smoke-exposed red wine, 84 samples had guaiacol concentration in the range of 0-5 μg/L, 159 samples had guaiacol concentration in the range of 5- 10 μg/L. Most of the samples had 4-methylguiacol less than 3 μg/L. In red smoke exposure wine, the average ratio of free guiacol to 4-methylguaiacol was 4.5. But the average ratio of total guaiacol to 4-methylguaiacol was 6.5, higher than the free forms.

A total of 86 control wines were randomly selected from 2013-2016 vintages with about 20 samples from each year. The samples were obtained from industry fermentation without barrel aging. Both free and total volatile phenols were analyzed. Multiple statistical methods were used to analyze the data. Univariate data analysis was used to identify differences between the control and smoke-exposed red wine. The results showed that except for free 4-methylguaiacol and bounded m-cresol, all compounds were significantly higher in smoke-exposed wine. Statistical analysis suggests that the total p-cresol is the best biomarker of smoked wine.

Investigation of Different Winemaking Protocols to Mitigate Smoke Taint Character in Wine

AVF Proj. ID: 2247 / /Cat.:
Primary Investigator(s): Dr. Anita Oberholsterby

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.

Measuring Grape Smoke Taint Protection

AVF Proj. ID: 2343 / /Cat.: ,
Primary Investigator(s): Andrew Waterhouseby

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

AVF Proj. ID: 2360 / /Cat.: ,
Primary Investigator(s): Elizabeth Tomasinoby

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

AVF Proj. ID: 2312 / /Cat.: ,
Primary Investigator(s): Michael C. Qianby

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

AVF Proj. ID: 2247 / /Cat.: ,
Primary Investigator(s): Anita Oberholsterby

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.