Wine Compound Interactions That Cause Perceived Smoke Taint in Red Wines.

Objective 1:  Evaluate and select Pinot noir and Cabernet Sauvignon wines that contain various levels of smoke taint.

As detailed in the previous years report more than 120 wines were collected that have various levels of smoke taint. The majority of wines (~100) were Cabernet Sauvignon and Pinot noir, but a few other varietals were also included such as Petit Verdot, Merlot and Syrah. Sensory analysis for these wines were completed in August 2023. We spent 9 months, running weekly sensory panels. This was longer than anticipated but we managed to collect a significant number of smoke impacted wines and did not want to miss the opportunity for larger data set, which can result in stronger causation in the last objective. At the start of each term panelists went through training and they also had retraining after 5 weeks, half way through the 10 week school term. The sensory protocol that was used can be found in Fryer and Tomasino (2022).

Objective 2:  Measure the volatile and nonvolatile chemical composition of the wines from Objective 1.

Measurement of volatile compounds are in progress. We are about half way done with this analysis. The protocol for volatile analysis was adapted from Zhang et al. 2023. We are about 3 months behind on the chemical analysis due to an installation delay with the liquid nitrogen tank used to provide gas to the equeipment and several compounds (utilized as chemical standards) that were back ordered. As of December 2023 analysis was able to recommence. Now that the sample prep for measuring smoke compounds (free volatiles, bound compounds and thiophenols) have been completed the student has started prepping for nonvolatile analysis at the start of January 2023. Free smoke phenols are being measured according to Liu et al. (2020) and bound smoke glycosides according to Caffrey et al. (2019). We are in the process of developing the method to measure the smoke thiophenols. The timeline in the 3rd year grant has been updated to reflect this change in timeline.

Objective 3:  Determine the chemical interactions causing smoke taint perception in Pinot noir and Cabernet Sauvignon wines using fsQCA – this will commence once chemical testing is completed.

Objective 4:  Validate results for fsQGCA using sensory testing – this will commence once chemical testing is completed.

Achieving tropical fruit aroma in white wines: from winemaking to consumer acceptance.

Summary – Final Report

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.

In both micro ferments and larger research scale ferments the Skin contact and combination of skin contact and fermentation gradient resulted in wines with higher concentrations of esters and thiols.  Descriptive analysis (DA) showed that SC was significantly different from both FG and SCFG.  SC presented the most tropical fruit aromas, SCFG presented more stone fruit, and FG presented more honey and lemon/lime.  Liking, using a 7-point Likert scale, showed there was not a significant difference between treatments.  Emotional response, using a 5-point Rate-All-That-Apply (RATA) scale, showed significant differences for ‘calm’ and ‘disgusted’ emotions.  Although using Multiple factor analysis to investigate all the data it was shown that liking was associated with positive emotions which were also associated with tropical fruit aromas.

Together this research shows that skin contact and a fermentation temperature gradient have a positive effect on tropical aroma in Chardonnay wines.  Understanding the link between wine processing and quality and consumer desires is important as wine is subjected to different environmental conditions each year, and consistency can be difficult to achieve.  These conditions of winemaking using skin contact and fermentation temperature gradient would be recommendation for winemakers looking for this tropical fruit aroma sensory signature in Chardonnay wines.

Impact of malolactic fermentation timing and the use of non-Saccharomyces yeast during cold soaking on Pinot noir wine color and sensory properties. (2024-2704

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 addressed some of these concerns and determined the impact of MLF timing on Pinot noir wine chemical and sensory properties.  In addition, the use of non- Saccharomyces yeast during cold soaking and the potential impact on a concurrent MLF was determined.

The timing of MLF inoculation had a significant impact on color with wines produced using a concurrent MLF having lower color density and polymeric pigments.  Interestingly, lower color and polymeric pigment content was only present in concurrent wines that had undergone a cold soak.  While MLF timing affected color, the addition of Torulaspora delbrueckii during cold soaking did not.  For the sequential MLF treatments, there was no difference in color or polymeric pigment content in wines that underwent a cold soak compared to those that did not.  After nine months of aging, the color and polymeric pigment differences present at the end of MLF were no longer present.  Of note was that wines produced with a concurrent MLF increased in color while all other wines saw a reduction in color as is typical during aging.  In addition, all wines increased significantly in their polymeric pigment content.  While all treatments increased in polymeric pigments, the largest increases in polymeric pigment occurred for the three treatments that underwent concurrent MLF.

While measurable color differences in the wines declined during aging, sensory analysis did reveal color differences between some treatments.  Wine produced with a concurrent MLF was noted to be more violet in color than other wines while wine produced with cold soaking + T.delbrueckii + concurrent MLF had higher red intensity.  The more red colored wine was also liked significantly more than the other wines when evaluated in clear glasses.  However, there were no differences in liking when black glasses were used emphasizing the effect of color on liking.  Sensory evaluation also revealed significant differences between the wines in aroma and mouthfeel.  Wines produced without cold soaking had significantly different aroma than those produced with a cold soak, and non-cold soak wines were also significantly different from each other due to MLF timing.  In contrast, timing of MLF did not impact the aroma of the cold soaked wines, whether an addition of T. delbrueckii had been made or not.  Non-cold soaked wines made with a sequential MLF were described as having cedar, fruity, and herbal aromas while those made with a concurrent MLF were described as having spicy, dried fruit, and woody aromas.

Cold soaked wines made with a sequential MLF had dark berry fruit and leather aromas.  For mouthfeel, the major differences were between wines that had T. delbrueckii added and those that did not.  Cold soaked wines with an addition of T. delbrueckii produced wines with desirable mouthfeel characteristics such as smooth, soft, and balanced.

Wines produced in 2023 included an additional variable, the use of Lactiplantibacillus plantarum to conduct MLF.  As was seen with the 2022 wines, the use of T. delbrueckii and/or conducting concurrent MLF had minimal impact on the speed of the alcoholic fermentation.  MLFs conducted by L. plantarum proceeded rapidly due to the higher inoculation rate but those conducted by O. oeni also completed MLF in 14 days or less.  Early analysis of color and phenolic properties shows different color trends between wines produced with concurrent MLFs induced by O. oeni or L. plantarum.  Polymeric pigments  trended higher  in concurrent MLFs with L. plantarum compared to O. oeni, except for concurrent MLF wines with an addition of T. delbrueckii (no cold soak).  Further analysis of these wines will determine which variables are significant as well as any significant interactions between the treatments.

Smoke Taint Sensory Interactions

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.

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

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.

Investigating Fruitiness Perception in Red and White wines

This provides results and conclusions from the entire project, although we may refer to previous reports. We have had a very exciting accomplishment with the adaptation of a chemometric method that can calculate chemical interactions resulting in specific sensory perceptions. This method, fuzzy set qualitative comparative analysis (fsQCA), overcomes the issues with traditional correlation analysis that made determining aroma chemical interactions very difficult. To date we have investigated 87 different compound combinations and their impact to fruit aroma in Pinot noir wine. By applying fsQCA we have found 5 compound sets that result in red fruit aroma in Pinot noir wine and 2 compound sets that result in dark fruit aroma in Pinot noir wine. The necessary and sufficient conditions found in these sets are supported by other work, but our results are the first to show the multiple combinations of compounds that can result in specific fruity aromas. We have also investigated 57 compound combinations for fruitiness in white wine. Since we were less sure about the calibrations used for fsQCA we ended up creating unique set variables to determine the necessary and sufficient conditions for different fruity aromas in white wine. Overall we found 5 compound sets that cause tropical fruit aroma, 2 compounds sets that cause red apple aroma, 1 compound set for pineapple aroma, 2 compounds sets for pear aroma, 4 compound sets for peach aroma, 1 compound set for orange aroma and 1 compound set for lychee aroma. For the compounds we investigated we did not get any compounds sets for citrus aroma and green apple aroma. We also incorporated nonvolatile factors into the analysis. In red wine we are investigating the effect of phenolic composition on fruitiness perception and in white wine we changed the residual sugar and ethanol concentration to determine its impact on fruity perception in white wines. Phenolic content in red wine was found to alter fruitiness perception, but the change in ethanol and sugar in white wine did not have an impact to aromas perception. This work has shown huge strides in understanding compound interactions that cause specific aromas in wines. To the point that we will be able to start building predictive models in the future that have much better success than any previous ones. With these models it will be possible to determine the impacts of different viticulture and winemaking practices to these wines without having to go through lengthy sensory studies and make real time decisions during the season for the desired wine quality parameter.

Development of a Tribology Method to Assess Mouth-feel Perceptions of Red Wines

We have successfully extracted and chemically characterized red wine with tannins, as well as the interactions between red wine tannins and salivary proteins by chemical methods. The effect of tannin-protein interactions on friction forces has been introduced. A tribology method has been developed to show an effect of red wine tannin on mouth lubrication. The formation of turbidity had the strongest relationship to the sensory effect of astringency.
This research has successfully chemically characterized tannins and the consequences of their interaction with saliva or proteins. The tribology experiments carried out on the two red wines with different lubricant (saliva or mucin) has also given promising results, and received much attention in the press. The research is continuing with Watrelot and Kuhl.

Characterization of Aroma Volatiles and their Glyosidic Precursors in Grapes and Wines

Summary: The complex aroma of wine is derived from many sources, with grape-derived components being responsible for the varietal character. The ability to monitor grape aroma compounds would allow for better understanding of how vineyard practices and winemaking processes influence the final volatile composition of the wine. Previously we developed a procedure using GC-MS combined with solid-phase microextraction (SPME) for profiling the free volatile compounds in grapes and wines. We also developed a method for monitoring the ‘aroma potential’ of grapes and wines without the need for initial isolation of the glycoside precursor fraction. However, this method still depends on indirect measurement of the glycosides and acid or enzymatic hydrolysis is needed to release the volatile aglycone which can result in artifact formation. In the current project we validated a novel method using UHPLC-qTOF MS/MS for direct analysis of intact aroma glycosides in grapes with minimal artifactual changes in composition. Using this method we tentatively identified 27 monoterpene glycosides including two monoterpene trisaccharide glycosides, tentatively identified for the first time in any plant. We measured the terpene glycosides in six cultivars at three maturity time points and demonstrated differential profiles depending on cultivar and maturity. We also modified the method so that it can be used to monitor monoterpene glycosides in wines and during winemaking. We have analyzed the glycoside content during fermentation for wines made in fall 2016 and 2017 with different varieties (Chardonnay, Merlot, Cabernet Sauvignon) and winemaking/processing methods. Monoterpenyl glycoside profiles differed between the grapes and the first alcoholic fermentation samples. In red wines, malonylated monoterpenol glucosides and monoterpenol hexose-pentoses decreased after the completion of alcoholic fermentation. We also measured the volatile composition of the wines during fermentation and we have started to relate changes in terpene volatiles to changes in the glycoside profiles. This work sheds important insight into possible biochemical changes in glycosylation during grape berry maturation. In addition, this research will allow us to better understand the effects of viticultural and winemaking practices on grape and wine components that affect flavor.

Investigating Fruitiness Perception in Red and White Wines

This report details activities that occurred from February 2018 – January 2019. The final date of this project is August 2019 and the next 6 months will include completing the last of the sensory panels and combining all data analysis. A final report will be submitted in January 2020. We are still slightly behind on the timeline due to issues detailed in last year’s report and we also had to renew our IRB (human ethics approval) in June 2018. Once the renewal is submitted it is illegal to run sensory tests on the project until approval is given, which was obtained in September 2018. In January 2019 we completed the last of the Pinot noir sensory panels, although we have not yet done data analysis on the January 2019 panel. Also as stated previously, we have not been able to complete any predictive modeling, some initial reviewer comments said that this objective might have been too ambitious in the timeline and after the 1st year we have to agree and have since removed this objective. We plan on working on predictive modeling in the future but this would be after the current grant is completed.

To date we have investigated 80 different compound combinations and their impact to fruit aroma in Pinot noir wine. We have also completed a panel that shows the influences of phenolic content on fruity aromas in Pinot noir and one panel that shows the impact of ethanol content on fruity aroma in Pinot noir. We have 2 potential marker compounds for red fruit aroma in Pinot noir and 4 red fruit solution sets using fsQCA that show the cause of red fruit aroma in Pinot noir. We have also found 5 solution sets for dark fruit aroma in Pinot noir using fsQCA.

We have also investigated 49 compound combinations for fruitiness in white wine. We are still working on using fsQCA to analyze this data. Preliminary results suggest a combination of low thiols and high esters are responsible for tropical fruit aromas, low to no esters are needed for citrus aromas, and esters and terpenes cause pear, peach and apricot aromas.

We will be running the last 4 Pinot gris sensory panels from February2019-June 2019 and completing the final data analysis. We are in the process of writing the first paper for publication and have done 2 presentations at domestic conferences on the analytical data analysis. Spring /Summer 2019 we will be presenting at 4 different international conferences in Europe and have plans for at least 3 more peer-reviewed publications.

Characterization of Bitter and Astringent Proanthocyanidins During Winemaking

Project Title: Characterization of Bitter and Astringent Proanthocyanidins during


Principal Investigators

  • Dr. Susan E. Ebeler, Department of Viticulture & Enology, University of California, Davis,


  • Dr. Hildegarde Heymann, Department of Viticulture & Enology, University of California,

Davis, 530-752-0380


Polyphenols, including proanthocyanidins (i.e., tannins), are widely distributed in foods and

beverages, including grapes and wines and they are key constituents impacting bitter and

astringent perception. Due, at least in part, to their chemical complexity, the changes in

proanthocyanidin concentration and chemical structure that occur during winemaking and that

impact sensory properties have not been fully evaluated.

During the past year we have developed an ultra-high performance liquid chromatography

quadrupole time-of-flight mass spectrometry (UHPLC-qTOF MS) approach to characterize the

subunit composition and molecular weight/average degree of polymerization of wine

proanthocyanidins. Wines with different maceration treatments were analyzed and we are in the

process of completing the data analysis and comparison of the treatments. This work is

beginning to provide important insight into the impact of maceration treatments on

proanthocyanidin composition of wines.