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.

Smoke Taint Sensory Interactions

AVF Proj. ID: 2694 / /Cat.:
Primary Investigator(s): Elizabeth Tomasinoby

Evaluate and select Pinot noir and Cabernet Sauvignon wines that contain various levels of smoke taint During the first few months of this project I recruited a student to perform this project. We also managed to collect 120 wines, Pinot noir and Cabernet Sauvignon, from industry collaborators that have had some level of smoke impact. Wines were primarily from the 2020 vintage and many were from winemaking tirals, of which we have the trial information. We have started doing sensory analysis of the wines to determine the level of smoke impact. Sensory procedure we are using can be found in (Fryer and Tomasino, 2022). Panels are happening weekly and all wines are being evaluated in duplicate. We are evaluating 10 wines per week, and have sensory panels scheduled through March 2023. After each sensory panel we are pulling 50 mL samples for future chemical analysis. All samples are being stored at -80°C. Storage at the temperature is very important to ensure that no changes happen with the wines during storage. Wines that have been stored in December have started to go through sample prep for bound smoke glycoside analysis, as both bound and free analysis of wines are scheduled to start in March 2023. After the smoke analysis is done we will move onto other compounds.

Raman for Smoke Exposure

AVF Proj. ID: 2711 / /Cat.:
Primary Investigator(s): Michael Qianby

During the 2022-2023 funding cycle, we have finished the volatile phenol analysis of 82 wine samples having various degrees of smoke exposure and about 60 pooled samples from different wineries. Those samples will be used for Raman spectra collection once the nanoparticle and Raman signal enhancement protocol is finalized. We have collected grape samples throughout the 2022 season from eight vineyards in California and Oregon and an enology lab. Out of the 214 independent samples, 180 are pinot noir. The samples were collected between September 9 and October 24. About half of the samples were collected from Salem, OR, where the wildfire created a lot of worry during harvest. The lab offered us samples and enology test results in an anonymous way. More grape samples will be collected in 2023. All the grape samples will be analyzed in the 2023-2024 funding cycle simultaneously. Those samples will be used for Raman spectra collection once the nanoparticle and Raman enhancement protocols are finalized. Different sizes of silver nanoparticles have been synthesized, and the Raman enhancements were observed. However, the enhancement depends on the size, shape, and concentration of the nanoparticles. More nanoparticles with different sizes will be synthesized and evaluated in the 2023-2024 funding cycle in conjunction with a linker agent such as benzenethiol. An automated sampling system for the Raman Spectrometer was developed by Dr. Feng Ye’s team from Spectra Scientific company to replace manual spectra collection. The system is based on an alumina 3D printed 117 well plate to eliminate Raman interference from plastics. Because alumina is not stable at acidic pH, we will obtain another 3D printing plate and coat it with gold so it can be used for wine samples. 18 We have established benchmark results for the Raman fingerprints of wine samples, especially using a combination of steady-state electronic and vibrational spectroscopies in a table-top optical setup. We have implemented FSRS with a tunable Raman pump and probe pulses in a femtosecond laser amplifier system for assessing the smoke-exposed wine. We have combined FSRS with AgNPs to optimize conditions for SE-FSRS and achieve higher sensitivity than the resonance Raman enhancement alone. We are investigating nanoparticle receptors for smoke compounds to enhance the Raman signal. Raman spectrum of 82 smoke-exposed wines and 214 smoke-exposed grape samples (grape juice) were collected on the 1064nm FT-Raman system. We have developed an algorithm for machine learning. First, we applied a background subtraction algorithm to remove the Rayleigh scattering and background fluorescence. After backgrounds were removed, the intensities of each peak were captured through a regression algorithm. After the base models were built using average spectra, each sample was measured using juice or wine base models to report the intensity of each peak. Intensities of extracted peaks were subsequently analyzed using a correlation matrix and principal component analysis. The above metrics were fed into Orange Data Mining for data processing and ML development. The model showed an excellent correlation of Raman to titratable acidity. The undergoing research is to use nanoparticles for surface enhancement Raman Spectroscopy and smoke compound receptor to enhance the signal so that the GC-MS data can be correlated with the smoke compounds.

Malolactic Fermentation Timing and Color

AVF Proj. ID: 2704 / /Cat.:
Primary Investigator(s): James Osborneby

The malolactic fermentation (MLF) is a key process in the production of red wines and some white wines. While it is commonly conducted after the completion of the alcoholic fermentation (sequential), it can also be induced at the same time where Oenococcus oeni is inoculated shortly after the beginning of alcoholic fermentation (AF). While a concurrent MLF is typically completed in a shorter time period than a sequential MLF, it is often avoided due to concerns over the production of excess acetic acid, loss of color, and competition with the fermentative yeast Saccharomyces cerevisiae. Finally, the impact of concurrent MLF on the organoleptic qualities of red wines is relatively unknown and may present an obstacle for the adoption of this practice. This project seeks to address some of these concerns and determine the impact of MLF timing on Pinot noir wine chemical and sensory properties. In addition, the use of nonSaccharomyces yeast during cold soaking and their potential impact on a concurrent MLF will be explored. Initial experiments assessed the production of acetaldehyde by six different non-Saccharomyces yeast under cold soak conditions. All yeast grew well during the six day simulated cold soak and significant differences in the amount of acetaldehyde produced were observed. T. delbrueckii Alpha produced the highest concentration of acetaldehyde (71.8 mg/L) while H. uvarum and M. fructicola Gaia produced the lowest. While M. fructicola Gaia had been used in previous cold soak experiments, we decided to use T. delbrueckii Alpha for future Pinot noir cold soak experiments due to the high production of acetaldehyde observed and the potential significance of this compound for color formation and stability. In 2022 Pinot noir wines were produced with and without cold soak, with and without T. delbrueckii Alpha, and with a concurrent or sequential MLF. AFs were completed in ten days or less while all MLFs were completed within fourteen days. Only minor differences in the time to completion of AF or MLF were observed between the treatments suggesting that the use of nonSaccharomyces yeast during cold soak did not have an impact on the concurrent MLF and that the concurrent MLF did not impact the performance of the AF. Wines are currently being filtered and bottled and will be assessed by a sensory panel in summer 2023. Color analysis of the wines is also underway as is analysis of acetaldehyde concentrations throughout cold soak, AF, and MLF. Findings from this study will help determine the implications of MLF timing and the use of a non-Saccharomyces yeast in conjunction with a concurrent MLF. This will allow strategies to be developed for the use of MLF and non-Saccharomyces yeasts to improve Pinot noir wine color as well as the impact on other sensory characteristics.

Achieving Tropical Fruit Aroma in White Wines: From Winemaking to Consumer Acceptance

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

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 project specific 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 2 nd semester of 2020 have been to design and perform the winemaking experiment for objective 1, measure the basic wine quality parameters (pH, titratable acidity, malic acid, acetic acid, and ethanol content), and collect wine samples for the analytical chemistry analysis. Much of 2021 has been spent on developing the analytical methods to measure thiols and esters on wine samples from objective 1. Treatments that presented higher concentrations of both aroma families were scaled up in objective 2. Winemaking experiment for objective 2 was performed and juice and wine samples were collected for basic wine quality parameters and analytical chemistry analysis. Treatment wines were bottled and stored for sensory descriptive analysis (objective 2) and consumer testing (objective 3). We are currently designing and recruiting panelists for sensory analysis and extracting free thiols for HPLC analysis for wines in objective 2, and purchasing chemicals for thiol precursor analysis for wines from objective 1 and 2. We are on schedule for this project except for the thiol precursor analysis which has been delayed due to the standards being backordered. They are anticipated to ship in March 2022.

Baseline Levels of Smoke-related Volatiles and their Glycosidic Precursors in California Grapes and Wines

AVF Proj. ID: 2595 / /Cat.:
Primary Investigator(s): Dr. Susan Ebeler and Anita Oberholsterby

The increasing incidence of wildfires in grape growing regions of California and the West Coast has highlighted the need for enhanced understanding of the levels of volatile phenols and their non-volatile glycoside precursors that contribute to smoke taint off-flavors in grapes and wines. In this project, we measured ten volatile phenols in non-smoke exposed grapes to begin to understand baseline levels of these compounds in red and white grape varieties. Free and total levels of guaiacol, creosol, phenol, 4-ethylguiacol, o-, m-, p-cresol, 4-ethylphenol, 4- methylsyringol, and syringol were measured in grapes from different regions of California. Air quality data for these regions is also presented. We will obtain data over a minimum of two years in order to begin to assess year to year variability. We have submitted a proposal to continue this work in 2022-23.

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

Tropical Fruit Aroma in Wine

AVF Proj. ID: 2479 / /Cat.: ,
Primary Investigator(s): Elizabeth Tomasino, Ph.D.by

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 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 project specific 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 6 months have been to design and perform the
winemaking experiment for objective 1, measure the basic wine quality parameters (pH, titratable
acidity, malic acid, acetic acid, and ethanol content), and collect wine samples for the analytical
chemistry analysis. We have also performed a preliminary sensory descriptive analysis panel in
December 2020 (Projective Mapping combined with Ultra-Flash Profiling), but the results have
not been analyzed. Despite the Covid-19 lockdowns we are on track with this project and we are
currently developing a method to measure fermentation esters in the wines. To keep on track with
the project timetable we are working with a colleague at the University of Adelaide to have thiols
analyzed, as the access to the OSU MS facilities is limited due to COVID.

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.