Oxidation in wine production can result in loss or alteration of varietal specific aroma/flavor compounds.  Glutathione is a naturally occurring compound in wine which is produced in grapes as well as yeast and acts as a strong anti-oxidant which can protect delicate oxidizable wine compounds such as thiols, terpenes and norisprenoids.

This trial will assay the performance of glutathione and precursor molecules to enhance the concentration of glutathione in aromatic white wines.  Previous work has shown that glutathione concentrations can be elevated by the proper application of a proper glutathione supplement during fermentation. Findings from the previous trial established that the aromatic perception can be enhanced by elevation of glutathione concentration in wine as well as aid in the long term preservation of delicate flavor/aroma molecules.  This study will additionally look specifically at the impact of the elevated glutathione levels on the preservation of SO2 throughout the cellaring process of aromatic white wine production in both barrel and tank programs.

Experimental Questions: Can increasing the glutathione concentration in finished wines help the sensory characteristics of the wine? How does glutathione concentration impact the management of SO2 in the cellar post-fermentation through bottling?

Strategy: In parallel tanks or barrels use two different process regimens varying the application of Fresharom®® glutathione supplement in rose/white juice lots from the same vineyard.  Keep fermentation process conditions as similar as possible. Monitor free and total SO2 in cellar closely. Log all cellar manipulations such as topping, rack and return, QC/QA sampling, SO2 additions, capturing all possible opportunities for oxygen to enter the vessel for comparative analysis.

Control treatment vs Experimental for this trial is as follows:

No Fresharom® added control vs Fresharom® supplement added during fermentation.

Fresharom® should be utilized at a 300 ppm dose.

SO2 monitoring post-fermentation in cellar through bottling.

General Concepts

  • Juice should be identically sourced and processed in parallel for trial and experimental treatments.
  • Document a process map for handling of fruit/must/juice to include all SO2 additions, pick time/temp, enzyme name and dose, press regimen, time in process, inerting of press/tank(s), fermentation parameters (yeast, nutrients, Fresharom® addition, all other additions/adjustments and fermentation curve-time/brix).
  • In parallel tanks or barrel programs use two different process regimens only varying the addition of Fresharom® glutathione supplement to Sauvignon Blanc or Rose’ juice lots from the same vineyard.
  • Keep fermentation process conditions/additions as similar as possible. Source Control and Experimental fruit from the same vineyard keeping control and trial juices as homogeneous as possible.
  • At the completion of primary fermentation monitor SO2 in wines throughout the cellaring time and document all cellar manipulations and wine movements.

Which varietal(s)?

  • Rose’ (many varietals)
  • Sauvignon Blanc


Fresharom® at 300ppm at ~1/3 brix depletion

Sample – Time Points – Documentation

  • Juice sample Glutathione pre-fermentation (Freeze 45 mL in a 50 mL tube with SO2 added to 50ppm for future analysis)
  • Juice YAN and juice chemistry (pH, TA, SO2 other routine analyses)(Target 250-300 ppm YAN for fermentation)
  • Document yeast selection, preparation and yeast nutritional plan, all addition dose rates. Yeast recommendations – X16, VL2, X5, VL3, Delta
  • Glutathione post-fermentation (Freeze 45 mL in a 50 mL tube with SO2 added to 50ppm)(samples to be shipped to ETS Labs)
  • Document all SO2 additions throughout process
  • Free and Total SO2 post-fermentation and at least monthly in cellar post-fermentation
  • Document all cellar manipulations (topping, QC/QA checks, movements, etc) and dates of SO2 sampling, measurements and additions.
  • A420 wine color check
  • Sensory evaluation pre-bottling/pre-blending.

(Set aside 2 x 750 bottles of control and treatment)


  • Glutathione – ETS Labs
  • Free & Total SO2 – to be done by participating winery
  • YAN and Juice Chemistry – to be done by participating winery
  • A420 wine color check – to be done by participating winery
  • Sensory Evaluation, difference and preference testing – by ARC member sensory panel

ARC Summary

Trial commitments/completed trials                        19 / 10

ARC member tasting panel opportunities              4 (Edna Valley, Sonoma Co. Paso Robles, Santa Rosa)

Presentation of Stabulation Trial Wines                  3 Events, 6 wines presented (control and treatment for each)

ARC Seminar at the Unified Symposium Sacramento – Schug Carneros Estate Winery, J Lohr Vineyards

WiVi Central Coast  Paso Robles – Fresno State University, Gainey Vineyards

ARC Strategic Planning Meeting – A to Z Wineworks, Van Duzer Vineyards

Trial Results

There were both qualitative measurables (sensory evaluation – ARC panels, public tasting – ARC Seminar) and quantitative measurables (Glutathione and Iron – ETS Laboratory, A420, A280 – ARC members) for the Glutathione in wine trial.  A sensory evaluation was performed at a series of regional tasting events and also at the public ARC seminar presented in Sacramento the week of the Unified Symposium. The sensory evaluations were structured and data analyzed by Larry Brooks, Instructor for Sensory Analysis at Fresno State University. All of these tests were presented to the groups as a triangle/preference test. This is a test in which three glasses are presented blind to the tasters. Two of the three are identical, and one is different. The tasters have two tasks. First to identify correctly which two are similar and which one different. Secondly to make a preference between them. This type of test is recommended when there is a small group of technical tasters as was the case here. The probability of guessing correctly with this test is low – only one in six.

The number of correct answers to achieve a statistical variance of less than 5% depends on the number of tasters. For ten tasters it is seven. For twenty it would be eleven. Results were held to the 5% standard, which some hold to be overly rigorous for sensory work. It remains the scientific standard, but it should be kept in mind that this is a very high bar for the sensory realm.

Glutathione Measurement in Finished Wine

Over the course of two harvest seasons Fresharom® glutathione enhancing yeast nutrient supplementation of fermentations was completed in 17 separate trials.  The results are summarized in Figure 1 and the average increase in glutathione in the treated fermentations was two times (2x) that of the control fermentations. Past experimentation has shown that a level of ~12 to 15 ppm of glutathione is needed to provide oxidative protection from aroma decay. Higher levels may be even more advantageous. In the control fermentations (no Fresharom® added) the glutathione level was below that ascertained to be important for the oxidative protection of the wines in 10 of the 17 trials. In the Fresharom® treated fermentations of the deficient trials, the glutathione level was elevated to protective levels in all but two of the trials.

In the seven trials where the control fermentations had glutathione levels above the minimum for protection, the Fresharom® addition elevated the glutathione levels even further to levels well above the minimum for protection.

Figure 1. Glutathione measurement in wines from 2015 and 2016 trials

The effect of Fresharom® supplementation on the increase of glutathione in finished wine showed both yeast strain and winegrape varietal influences as previously reported in the MS thesis of Kritzinger, Stellenbosch University, 2012. Laffort yeast Zymaflore® VL3, VL2, X-PURE and Actiflore® Rose’ were all effective at increasing the final glutathione levels above the protection minimum. Sauvignon Blanc, Rose’ and Chardonnay all showed a positive response to glutathione enhancement, while Riesling was resistant to significant change in glutathione increase in both vintages.  These yeast and varietal observations are all tempered by the caveat of small sample size.

Interpretation of the effects of glutathione concentration on the varietal freshness of finished wines is predicated on the effect of glutathione, a powerful antioxidant, on the oxidation state of the wine and the prevention of oxidative damage to fragile aroma molecules.

To support the interpretation of the glutathione effects on aroma, measurements were made of Iron in the finished wines as well as the absorbance at 420nm for brown color influence by oxidized phenolics such as quinones and 280nm as a measure of total phenolics. Iron can be a key influencer of oxidative damage due to its initiation of the Fenton reaction and subsequent cascade of oxidative reactions through highly reactive radical intermediates such as hydrogen peroxide.

Figure 2. Spectral Data and Iron Concentration for Glutathione Enhanced Wines

As illustrated in figure 2, neither the absorbance data nor the Iron measurements indicate any abnormal chemical balances in the wines.  The Iron concentrations were all very similar and fairly low while the phenolic load (A280) and the oxidative browning (A420) of the wines were all similar and seemingly insignificant.  The interpretation of the impact of glutathione on the aromatic freshness of the wines would not seem to be impacted by either Iron or phenolic chemical balance or reactivity.

ARC Member Winemaker Tasting Panel Sensory Evaluation

Over the course of four months, four different ARC member tasting panels were convened where Fresharom®/Glutathione trial wines were evaluated.  A total of 11 wines were evaluated in 13 separate tastings.  In those 13 tasting opportunities there were 9 examples of statistically significant differences detected.  In a cumulative data analysis, of the 9 wines determined to be different the preference was 8 for the Fresharom®/Glutathione treatment and 1 for the standard control process. These results clearly indicate the positive effect on wine perception by increased glutathione concentration in the wines.  The enhanced perceptions of fruitiness, crispness, acidity and freshness were most prevalent in observational comments by the tasting panelists.

Figure 3. Sensory Evaluation Data for Glutathione Trial.

ARC Seminar at the Unified Symposium Sensory Evaluation

An ARC seminar public event was held during the week of the Unified Symposium in Sacramento in January 2016. Attendance of over 120 wine industry professionals including production, marketing and publishing personnel formed a large and diverse industry group and provided a unique opportunity for evaluation of the ARC Glutathione trial wines.  Two ARC member wineries took part in providing their wines for evaluation.  A blind tasting was held with feedback from the participants including some personal and industry demographic data as well as difference and preference evaluations for the two separate control/treatment wine pairings.

The tasting was structured by Larry Brooks, 2016 Fresno State University instructor for wine sensory evaluation.  Mr. Brooks also analyzed the resulting demographic and sensory evaluation data. The demographics showed a bias towards male representation at this event, not dissimilar to the proportion of production employees in the wine industry.  The age and professional experience of the participants indicated a very experienced group.

Figure 4. Participation and Sensory Preference Data from ARC Unified Symposium Seminar Tasting Event

With 96 seminar participants taking part in the tasting event, this marked the largest panel to evaluate these trial wines. A very strong result of preference for the Fresharom® treated wines for both trials supported the previously determined ARC member winemaker panel results. A very strong preference, at a margin of error of only 0.01% had the Schug Carneros Sauvignon Blanc Fresharom® treated wine preferred by a margin of 62 to 32. The Schug Sauvingon Blanc was fermented with the Laffort Zymaflore® DELTA yeast and the glutathione increase was up 8.2ppm from 18.4ppm up to 26.4ppm A similar, but slightly weaker preference, with a margin of error at 0.05%, had the J Lohr Central Coast Sauvignon Blanc Fresharom® treated wine preferred by a margin of 56 to 32. The J Lohr Sauvignon Blanc was fermented with Laffort’s yeast Zymaflore® VL3 and the glutathione increase was up 12ppm from 14.8ppm up to 26.8ppm

Case Study A – Sonoma-Cutrer Vineyards

Sonoma-Cutrer has been an active ARC member since the group’s inception. As such the winery participated in both vintages of the Glutathione trials.  In the 2015 vintage of Chardonnay fruit, Sonoma-Cutrer winemaker Cara Morrison added implementation of the trial with the added variables of yeast and tannin addition. She selected two different yeast, Laffort’s Zymaflore® VL2 and Zymaflore® X-PURE, and also added the variable of fermentation tannin addition at 50ppm (Figure 5). In a subsequent vintage Cara utilized the commercial yeast CY3079 in a parallel trial with Fresharom®.

Figure 5. Glutathione Trial Wine Chemistry

As evidenced by the data in figure 5 the trial variables had little to no influence on the measurable chemistry of the finished wines. There were slight differences in residual sugars and malic acid which may have a slight impact on the sensory evaluation of the wines.

A panel consisting of Sonoma-Cutrer winemakers and Laffort personnel participated in a blind tasting of the wines from the trial.  Figure 6 lists the wines, the volumes produced and the forced ranking preference as determined by the tasting panels’ combined scores.  The Fresharom treated wines were preferred for both yeast strains tested while the tannin addition was ranked last in each flight. The wines were very young so the tannin addition may have had an exaggerated effect due to the timing of the sensory evaluation.

Figure 6. Sensory Preference for Glutathione Trial Wines

Sonoma-Cutrer used three different yeast strains in Fresharom® glutathione enhancement trials over the course of two vintages (Figure 7). Results show that glutathione levels that were well below those needed for aroma protection can be elevated to protective levels.  Sensory evaluation also indicate that the Fresharom® treated wines are preferred.

Figure 7. 2015 and 2016 Vintage Glutathione Trial Results

Case Study B – Castoro Cellars

The glutathione trial at Castoro Cellars was done using Sauvignon Blanc fruit.  The control and treatment lots were 5000 gallons each. The fruit was machine harvested and 40ppm SO2 was added at the crusher. Lafazym Extract was added at 20 gm/ton in the press and the juice was centrifuged with a solids target of 50 NTU within 20 hours. The juice had a pH of 3.60 and a TA of 6.4 gm/L at 21.4 brix.

Fermentation was initiated with Zymaflore® VL3 yeast and all adds except Fresharom® were identical in both control and treatment lots. Fresharom® was added to the treatment lot at 300ppm when the fermentation was at 16 brix. Fermentation proceeded for both control and treatment lots through completion with negligible differences.

Figure 8. Brix Depletion and Temperature Plots for Control and Glutathione Fermentations

The wines were kept in stainless steel tanks in cellar and the SO2 regimen was monitored and recorded. On October 4 both lots received a 40ppm addition and on October 22 both lots received a 30ppm addition. Both lots exhibited similar response to the SO2 additions and no chemistry changes were observed.

The glutathione level in the control wine was measured at 8.4ppm after primary fermentation while the Fresharom® treated wine was measured at 13.8ppm, above the minimum level for oxidation protection. When the Castoro Cellars Sauvignon Blanc was presented in blind at an ARC member winemaker tasting panel, a statistically significant difference was determined by the panel with the preference being for the Fresharom® treated wine with a 0.01 margin of error.

Figure 9. Glutathione Trial Wine Chemistry

While the chemistry remained unchanged in any significant way, the sensory preference for the treated wine with an elevated glutathione level was determined.

As shown in consecutive vintages the level of glutathione in finished wines can be elevated with the proper application of a yeast nutritional supplement, in this trial, Fresharom® from Laffort. The level of glutathione needed to impact sensory properties of wine has been shown to be anywhere from 10 to 15ppm.  We saw many examples where non-supplemented juice was well below the impact level of glutathione and was able to be elevated to impactful levels by supplementation.  The sensory evaluation of the treated wines validated the aroma improvements associated with elevated glutathione levels in finished wines.

The empirical observation of a positive impact on the SO2 management in the cellaring of treated wines was investigated in year two of this study, however due to a limited number of data points reported, it was impossible to come to any conclusions regarding this past observation.

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