Report

LEES MANAGEMENT

 

Introduction

In white winemaking ageing on the lees, or sur lie ageing, is frequently used to enhance many properties of the wine including both aesthetic and physical characteristics.  The autolysis of yeast cells after alcoholic fermentation releases many compounds which impact the final properties of the wine, most notably the sensory characteristic of mouthfeel/weight/volume is enhanced.

The properties of tartaric acid stability and protein stability can also be impacted. The release of yeast components from autolysis can also improve subsequent malolactic fermentation as nutrients for the ML bacteria if MLF is desired for the specific wine.

In this trial the mouthfeel character of the wine is the focus.  Use of frequent stirring over time is the main manipulation used in cellar for sur lie aged wines.  The use of specific enzyme blends containing B-glucanase and pectinase enzyme activities may also enhance the sur lie character of wines over a shorter timeline thus reducing the cellar risks of spoilage and flavor deterioration related to microbial risk as well as oxidation. Accelerated sur lie character can also lead to bringing the wine to bottle sooner.

Experimental Question: Which white wine lees management options deliver the most impact? Which wine quality parameters are most impacted by different lees management practices?

Strategy: In parallel tanks or barrels use two different process regimens in the lees management of white wine lots from the same vineyard.

Control treatment vs Experimental for this trial is as follows:

Control will be standard cellar practice for sur lie aging including documentation of the stirring method and timing.

The treatment for this trial will be a B-glucanase/pectinase enzyme addition (Laffort enzyme Extralyse) using identical cellar practices as control.

*Use of a sur lie adjunct such as Laffort Oenolees may also be evaluated post-sur lie ageing as an added level of trial complexity.

Scope

Varietal Application – Chardonnay, other sur lie program white wines as agreed upon

Process conditions – Barrel Program or Tank Program

Stirring mechanism, tools and frequency and duration are critical factors to record consistently and accurately

The general procedural guidelines listed below may not be ideal for all participating wineries and some variation may occur.  The winery variability was discussed in project harmonization meetings before harvest and all changes were determined to be acceptable.  The slight processing variations builds robustness into the trial and in no way eliminates the individual trial iteration from proper comparison with other trials.

General Concepts

  • Experimental Question: Which white wine lees management options deliver the most impact? Which wine quality parameters are most impacted by different lees management practices?
  • Strategy: In parallel tanks or barrels use two different process regimens in the lees management of white wine lots from the same vineyard, juice source tank or wine post-fermentation.
  • Wine should be taken through alcoholic fermentation and be ready for cellar ageing. MLF should be completed if desired for the specific wine.

Varietal(s)

  • Chardonnay

Dosages

  • Laffort Extralyse should be dosed at 10 g/hL and held for a minimum of 3-6 weeks
  • Laffort Extralyse should be added directly after primary fermentation is completed

Sample – Time Points – Documentation

  • Document all basic fermentation parameters such as temperatures and brix drop.
  • Document a complete log of additions including enzymes, tannins, fining applications, yeast selection, yeast rehydration protocol, yeast nutrition regimen and any other additions should be kept.
  • Post-fermentation wine chemistry – pH, TA, EtOH, SO2, VA, etc – should be documented (ARC member winery analysis).
  • Once the wine is ready for cellaring, baseline measurement of stirred NTU should be captured as a measure of total wine solids/yeast content, this will be the “substrate” for autolysis and yeast contribution to sur lie character. Target NTU/% solids TBD. Dilutions may be necessary to get accurate readings depending upon meter.
  • Strict records of all cellar manipulations of the wine should be documented with the most critical being the stirring frequency, mechanism and duration. Log cellar temperature throughout trial.
  • SO2 measurements and additions should be noted.
  • Lees Management Practices to consider and document thoroughly:
    • Barrel or Tank cellaring, volume, temperature
    • Time in barrel/tank
    • Stirring: frequency – mechanism – duration
    • B-Glucanase/Pectinase (Laffort Extralyse) dose and addition timing
    • *Laffort Oenolees addition (lees replacement) – after normal sur lie ageing is completed as an adjunct
  • Samples of control and experimental treatment should be taken at 6 to 8 weeks post-fermentation (Laffort Extralyse addition) for polysaccharide and mannoprotein analysis (SARCO). (1 x 750 mL)
  • Amount of bentonite needed for protein (heat) stability (80C for 2 hrs, less than 2 NTU change).
  • % DIT, (log whether doing Laffort CeLstab-CMC KHT stabilization or traditional chill KHT stabilization)
  • Sensory evaluation pre-bottling/pre-blending.

Set aside 2 x 750 bottles of control and treatment) (timing of ARC member sensory panel TBD) Sensory evaluation of wines at blending/bottling – as late as possible with trial lots kept separate (Difference, Preference and Descriptive – body/mouthfeel, complexity, intensity, sweetness testing).

Analyses

  • Wine chemical analysis – to be done by participating winery
  • Finished wine NTU – to be done by participating winery
  • % DIT – My Enologist
  • Total Polysaccharide and Mannoprotein – SARCO Laboratory (Bordeaux, France)
  • Sensory evaluation – ARC member panel

ARC Summary

Trial commitments/completed trials                        24 / 17

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

Presentation of Lees Management Trial Wines                    5 Events, 13 wines presented (control and treatment for each)

ARC Seminar at the Unified Symposium Sacramento – Sonoma-Cutrer Vineyards, Benziger Family Winery

Oregon Wine Symposium Portland – Grand Moraine Winery, Edgefield Winery

WBM Innovation & Quality St Helena –Sonoma-Cutrer Vineyards, J Lohr Vineyards and Wines

WBM WiVi Central Coast Paso Robles – Hope Family Wines, Castoro Cellars

ARC Strategic Planning Meeting Santa Rosa – Grand Moraine Winery, Sonoma-Cutrer Vineyards, Judds Hill Winery, J Lohr Vineyards and Wines, Frank Family Winery

Trial Results

There were both qualitative measurables (sensory evaluation – ARC panels, public tasting – ARC Seminar) and quantitative measurables (% DIT – My Enologist, Total Polysaccharides and Mannoproteins – SARCO Laboratory, Bordeaux, France, Wine Chemistry – ARC members) for the Lees Management/Sur Lie Aging 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.

% DIT; Degree of Tartaric Instability

The trial goal of acceleration of the sur lie aging character of the wines is certainly a qualitative factor and is best determined by sensory evaluation.  In the course of sur lie aging many characteristics of the wine are modified (Laffort MP40 patent), some in a measurable fashion. One of the factors which can be impacted is the tartrate stability of the wine, a property mediated in part through the release of a specific 40 kDa protein from the yeast Saccharomyces as the cells degrade and release their components into the wine.

The measurement of the DIT, or degree of tartrate instability, could serve as a marker for the progress of the sur lie aging of the wine.  In order to test for this a DIT analysis was performed on the ARC trial samples by the commercial laboratory My Enologist in Napa CA.

The samples were taken approximately six to eight weeks post-fermentation and the data in figure 1 shows no consistent trend in tartrate stability across the samples for this sampling time point.

Figure 1. DIT Analysis of select Lees Management Trials

Total Polysaccharides and Mannoproteins

The desired sur lie character of wines in multi-dimensional.  One of the predominant characteristics is an increased perception of volume, mouthfeel, weight and sweetness. While this perception is best evaluated by sensory analysis the molecules thought to mediate most of the effect of these characteristics are polysaccharides and mannoproteins released into the wine as the yeast lees go through autolysis.

Wine samples were submitted to the SARCO Laboratory in Bordeaux France for total polysaccharide and mannoprotein analysis by HPLC.  The results reported in figure 2 show that most of the trial resulted in an increase in the polysaccharide and mannoprotein content up to 25%.

There were six samples submitted that in sensory evaluation showed a statistically significant difference and also had a statistically relevant preference for the treated wines. Of those six wines where the treatment was preferred, three had a significant increase in total polysaccharides and mannoproteins, while 2 had insignificant differences and one displayed a reduction.

The preferred wine that exhibited a decrease in total polysaccharides and mannoproteins may have been influenced by the timing of the sample used for analysis versus the timing of the sample taken for sensory evaluation.  The analytical sample was from an early time point before the wines were showing much differentiation while the tasting sample had spent more time in cellar.

Figure 2. SARCO Laboratory total polysaccharide and mannoprotein measurement

ARC Member Winemaker Tasting Panel Sensory Evaluation

Over the course of four months, four different ARC member tasting panels were convened where Extralyse® treated Lees Management trial wines were evaluated.  A total of 14 wines were evaluated in 23 separate tastings.  In those 23 tasting opportunities there were 8 examples of statistically significant differences detected.  In a cumulative data analysis, of the 8 wines determined to be different the preference was 8 for the Extralyse® Lees Management treatment and 0 for the standard control process. These results clearly indicate the positive effect on wine perception by beta-glucanase/pectinase treatment in the sur lie aged wines.  The enhanced perceptions of roundness, volume and sweetness were most prevalent in observational comments by the tasting panelists.

The timing of the sensory panels had a profound effect on the outcomes.  The early panels which were held in early December and January were approximately five to six weeks post fermentation while the ARC Seminar at the Unified was approximately eight weeks post fermentation. These early evaluation opportunities yielded observations where no difference was detected in the wines. The Wine Business Monthly Innovation & Quality and WBM WiVi Central Coast in early and mid-March, respectively, and the ARC Strategic Planning Meeting in late March provided later time points for evaluating the wines.  The later sensory evaluations showed that differentiation was occurring and that the treatment was unanimously preferred in all eight wines tasted at that time point.

Figure 3. Sensory Evaluation Data for Lees Management 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 Lees Management 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. This evaluation took place approximately ten weeks post-fermentation and the results showed no statistically relevant differentiation of the wines.

In an informal tasting at a Benziger Family Winery days before the ARC Unified Seminar event, five panelists including Benziger winemakers, enologists and Laffort ARC personnel found differentiation between the treatments of the Lees Management trial as well as additional treatments undertaken at Benziger including an Oenolees application and a combination Extralyse and Oenolees application. The preference was for the treated wines with the combination treatment grading out as most preferred. These results are informal and the sample size too small for meaningful statistical evaluation, but bear mentioning due to the experience of the panel and the controlled environment the tasting took place in.

Case Study A – Blenheim Vineyards, Virginia – Winemakers Research Exchange

Chardonnay Lees Management with Extralyse (ARC)
Blenheim Vineyards
Submitted by Kirsty Harmon

Summary


This study examined the impact of lees stirring and batonnage enzyme addition during Chardonnay aging on the chemical and sensory qualities of the wine.  It is a companion study to Blenheim’s Chardonnay Lees Management (2016), which compared the effects of not stirring Chardonnay to stirring Chardonnay.  Chardonnay juice was fermented in barrels, and afterwards two different treatments were imposed: stirred, and stirred with Extralyse (Laffort).  Stirring occurred once per week for 8 weeks.  No major chemical differences could be observed between the finished wines. Wine tended to become more cold stable over time.  Additionally, increased bentonite additions to become heat stable were necessary after aging.  In general, people often could not distinguish between stirring and stirring with Extralyse.  When people could distinguish, there appeared to be a slight preference for wine made with Extralyse.  The descriptors used generally did not help elucidate which qualities in wine were affected by stirring.  There may be a small tendency for Extralyse to enhance Fruit Intensity and Depth of Flavor, but these tendencies were weak. However, the stirring regime for this study was relatively short (8 weeks).  In the future, more realistic stirring regimes should be implemented to see whether differences tend to increase over time.

Introduction

Marchal et al. (2011) provide an excellent brief review of yeast autolysis in their introduction.  Lees are mainly composed of yeast, bacteria, tartaric acid, polysaccharides, and protein-tannin complexes (Zoecklein 2013).  Heavy lees generally refers to lees which precipitate 24 hours after fermentation (generally grape particles and large complexes of other lees particulates), and can often lead to off-aromas in wine.  Light lees precipitate later and are generally beneficial to wine quality, and have less grape particulates and less heavily complexed yeasts and other lees particulates (Zoecklein 2005; Zoecklein 2013). Lees aging can decrease vanilla flavors from oak, and increase toasted flavors (Chatonnet et al. 1992; Tominaga et al. 2000).  Others have observed that lees stirring increases yeast character in the wine, decreases fruit and oak character.  In some cases, this reduction in oak character can increase the perception of fruit (relative to very oaky control wines) (Zoecklein 2005).

Lees aging also increases the polysaccharide content of wines, particularly mannoproteins, which may enhance wine protein and tartrate stability (Llaubères et al. 1987; Ledoux et al. 1992; Moine-Ledoux et al. 1997; Feuillat 2003; Zoecklein 2005; Zoecklein 2013).  Sur lies aging releases mannoproteins and other cell wall polysaccharides which can enhance the colloidal structure, stability, and aromatic quality of red wines while reducing their astringency, making sur lie aging of red wines important (Zoecklein 2005).  Although yeast-derived proteins can increase during lees aging, these proteins are not involved in protein instability (Zoecklein 1991).

Lees may also act to preserve fruity and varietal characteristics by preventing oxidation and producing a reducing environment (Marchal et al. 2011; Zoecklein 2013).  The release of thiols into the wine from yeast has been attributed to lowering reductive characteristics by being able to oxidize methanethiol and ethanethiol into their non-volatile disulfide forms (Lavigne and Dubourdieu 1996); however, this greatly depends on other factors in the aging process, and could impart a more reductive character to the wine.  Yeast glycoproteins from autolysis may also decrease astringency in wines through interaction with phenolic compounds (Escot et al. 2001).  Lees autolysis can also impart sweetness to wine (Zoecklein 2005; Marchal et al. 2001), which may be in part due to sweet peptide fractions released during cell autolysis.  One such fraction appears to be derived from heat shock proteins (Hsp12p) (Marchal et al. 2011), which is expressed from high temperature, ethanol, oxidative stress, and glycerol concentrations (Varela et al. 1995).  All of these factors are present under winemaking conditions (Marchal et al. 2011).  The breakdown of peptides can result in aromatic precursors in wines (Zoecklein 2005), but may also provide more nitrogen for spoilage organisms to consume.  Many of these impacts of lees aging can be affected by winemaking practices, such as frequency of stirring, amount of lees present, amount of oxygen ingress, pectinase/glucosidase enzyme additions (such as Extralyse by Laffort), and perhaps even quality of lees.  This study examines the impact of one such lees stirring regime on the chemical and sensory qualities of wine.

Results and Discussion

No major chemical differences could be observed between the finished wines. Wine tended to become more cold stable over time.  Additionally, increased bentonite additions to become heat stable were necessary after aging.

Juice Chemistry

Chemistry after Primary Fermentation

Wine Chemistry
Lab Results from Enology Analytics from Early January, 2017

Wine Chemistry
Lab Results from ETS and My Enologist from Early January, 2017

The wine was tasted at two different sensory sessions. In the January 25 session at Early Mountain Vineyards, of 37 people who answered, 13 people chose the correct wine (35%), and thus these wines were not significantly different.  In general, there was a slight preference for the treatment with Extralyse by those who chose the correct wine.   No strong trends were found between wines using the descriptors in this study.

In the February 15 session at Williamsburg Winery, 7 out of 10 judges were able to correctly distinguish the stirred from the stirred wine with Extralyse, suggesting that these wines were significantly different (p<0.05).  The wines were voted to have an average degree of difference of 3.1 (out of 10), suggesting that the difference between these wines was not great.  Of those judges that correctly distinguished the wines, out of 6 votes 33% of judges preferred the stirred wine and 66% of judges preferred with stirred wine with Extralyse. However, this number of judges is very small.  No strong trends were found between wines based on the descriptors used in this study.  Stirring with Extralyse had a slight tendency to increase Fruit Intensity and Depth of Flavor. 

In general, people often could not distinguish between stirring and stirring with Extralyse.  When people could distinguish, there appeared to be a slight preference for wine made with Extralyse.  The descriptors used generally did not help elucidate which qualities in wine were affected by stirring.  There may be a small tendency for Extralyse to enhance Fruit Intensity and Depth of Flavor, but these were not significant in these studies. These results may have been enhanced if the stirring regime was allowed to continue for a longer period of time, or if panelists had been trained more rigorously in descriptors and had had more replications.

Methods

Approximately 1.83 tons of Chardonnay were sourced from the same vineyard on 8/24, refrigerated at 50°F, and were whole cluster pressed on 8/26 for approximately 1250L of juice.  50 mg/L of sulfur dioxide were added at processing.  Bentonite (AEB Bentogran) was added at a rate of 30g/hL as the juice exited the press and was settled overnight at 35°F.  Tartaric acid was added at a rate of 1g/L to bring pH into a range of 3.4-3.6.  The morning after settling (8/27), the juice was racked off of sediment to another tank to ensure homogeneity.  Juice was then racked into two identical barrels.  Juice was allowed to warm to approximately 50°F and 15g/hL of EC1118 yeast was added to each barrel. Fermentation was monitored daily.

After alcoholic fermentation was complete (residual sugar as measured by enzymatic assay was 2g/L or less), samples were taken from each barrel for in-house post fermentation wine chemistry.  Additionally, samples were taken for heat stability and cold stability analysis.  Sulfur dioxide was added at a rate of 50mg/L.  These samples were taken before Extralyse addition or initiation of the stirring regime.  Extralyse was added at a dose of 8 g/hL to the second barrel and the stirring regime was started at 1 time per week for 45 seconds per barrel with a stainless steel barrel stirrer. Stirring was done by the same individual each time to ensure consistent and repeatable technique.

Post-Fermentation heat and cold stability were performed by ETS.  All cold stability trials on finished wine was performed by My Enologist.  All general wine chemistry on finished wine was performed by Enology Analytics.  The rest of the results were gathered in-house.  8 weeks after Extralyse addition occurred (December 2016), samples were taken of all barrels for polysaccharide, protein heat stability, cold stability, basic chemistry, and sensory analysis.

For the triangle test and preference analysis for the January 25 tasting, anybody who did not answer the form were removed from consideration for both triangle, degree of difference, and preference.  Additionally, anybody who answered the triangle test incorrectly were removed from consideration for degree of difference and preference.  Additionally, any data points for preference which did not make sense (such as a person ranking a wine and its replicate at most and least preferred, when they correctly guessed the odd wine) were removed.

In order to balance the data set to perform statistical descriptive analysis on the January 25 tasting, any judge who had not fully completed the descriptive analysis ratings were removed.   In order to then make the amount of judges between groups equivalent, two judges from group 2 were transferred to group 1, and then an extra judge was eliminated both from group 2 and group 3.  This resulted in a final data set of 3 groups, each with 9 judges (considered as replications within groups, and groups were considered as assessors).  Data was analyzed using Panel Check V1.4.2. Because this is not a truly statistical set-up, any results which are found to be statistically significant (p<0.05) will be denoted as a “strong trend” or a “strong tendency,” as opposed to general trends or tendencies.  The statistical significance here will ignore any other significant effects or interactions which may confound the results (such as a statistically significant interaction of Judge x Wine confounding a significant result from Wine alone). The descriptors used in this study were Fruit Intensity, Yeast Character, Depth of Flavor, Sweetness, Bitterness, and Body.

The procedures for analyzing sensory analysis were the same for the February 15 tasting.  In order to balance the data set for descriptive analysis, one judge was randomly moved from group 1 to group 3, to result in 3 groups each with 3 judges.

References

Chatonnet, P., Dubourdieu, D., and Boidron, J. N. 1992. Incidence des conditions de fermentation et d’èlevage des vins blancs secs en barriques sur leur composition en substances cèdèes par le bois de chêne. Sci. Aliments. 12:665–685.

Escot, S., Feuillat, M., Dulau, L., and Charpentier, C. 2001. Release of polysaccharides by yeasts and the influence of released polysaccharides on colour stability and wine astringency. Aust. J. Grape Wine Res. 7:153–159.

Feuillat, M. 2003. Yeast macromolecules: Origin, composition, and enological interest. Am. J. Enol. Vitic. 54:211-213.

Lavigne, V. and Dubourdieu, D. 1996. Demonstration and interpretation of the yeast lees ability to adsorb certain volatile thiols contained in wine. J. Int. Sci. Vigne Vin. 30:201–206.

Ledoux, V., Dulau, L., and Dubourdieu, D. 1992. Interprètation de l’amèlioration de la stabilitè protèique des vins au cours de l’èlevage sur lies. J. Int. Sci. Vigne Vin. 26:239–251

Llaubères, R.-M., Dubourdieu, D., and Villettaz, J.-C. 1987. Exocellular polysaccharides from Saccharomyces in Wine. J. Sci. Food Agric. 41:277–286.

Marchal, A., Marullo, P., Moine, V., and Dubourdieu, D. 2011. Influence of yeast macromolecules on sweetness in dry wines: role of the Saccharomyces cerevisiae protein Hsp12. Journal of Agricultural and Food Chemistry. 59:2004-2010.

Moine-Ledoux, V., Perrin, A., Paladin, I., and Dubourdieu, D. 1997. Premiers rèsultats de stabilisation tartrique des vins par addition de mannoprotèines purifièes (Mannostab). J. Int. Sci. Vigne Vin. 31:23–31.

Tominaga, T., Blanchard, L., Darriet, P., and Dubourdieu, D. 2000. A powerful aromatic volatile thiol, 2-furanmethanethiol, exhibiting roast coffee aroma in wines made from several Vitis vinifera grape varieties. J. Agric. Food Chem. 48:1799–1802.

Varela, J. C. S., Praekelt, U. M., Meacock, P. A., Planta, R. J., and Mager, W. H. 1995. The Saccharomyces cerevisiae HSP12 gene is activated by the high- osmolarity glycerol pathway and negatively regulated by protein kinase A. Mol. Cell. Biol. 15:6232–6245.

Zoecklein, B. 1991. Protein stability determination in juice and wine.  Virginia Cooperative Extension.  http://www.apps.fst.vt.edu/extension/enology/downloads/ProteinS.pdf.

Zoecklin, B. 2005. Lees Management. Enology Notes #106. http://www.apps.fst.vt.edu/extension/enology/EN/106.html.

Zoecklein, B. 2013. Nature of wine lees. Practical Winery and Vineyard. July.  http://www.apps.fst.vt.edu/extension/enology/downloads/wm_issues/Nature%20of%20Wine%20Lees.pdf.

Case Study B – Horton Vineyards, Virginia – Winemakers Research Exchange

Chardonnay Lees Management with Extralyse (ARC)
Horton Vineyards
Submitted by Michael Heny

Summary

This study examined the impact of lees stirring and batonnage enzyme addition during Chardonnay aging on the chemical and sensory qualities of the wine.  Chardonnay juice was fermented in barrels, and afterwards 3 different stirring regimes were imposed: unstirred, stirred, and stirred with Extralyse (Laffort).  Stirring occurred once per week for 8 weeks.  The finished wines showed decreasing levels of residual sugar with stirring and with enzyme addition.  Some malolactic fermentation could be observed in the stirred wine with Extralyse as well.  Wine tended to become more cold stable over time, but the unstirred wine showed the highest level of cold stability but also the highest level of bentonite addition necessary to become heat stable. These results suggest that stirring may enhance Sweetness, Depth of Flavor, Yeast Character, and Body, although many of these effects were weak.  The effect of Extralyse in combination with stirring was not too different than from stirring itself.  However, the stirring regime for this study was relatively short (8 weeks).  In the future, more realistic stirring regimes should be implemented to see whether differences tend to increase over time, particularly with respect to Extralyse.

Introduction

Marchal et al. (2011) provide an excellent brief review of yeast autolysis in their introduction.  Lees aging can decrease vanilla flavors from oak, and increase toasted flavors (Chatonnet et al. 1992; Tominaga et al. 2000).  Lees aging also increases the polysaccharide content of wines, particularly mannoproteins, which may enhance wine protein and tartrate stability (Llaubères et al. 1987; Ledoux et al. 1992; Moine-Ledoux et al. 1997).  Lees may also act to preserve fruity and varietal characteristics by preventing oxidation and producing a reducing environment (Marchal et al. 2011).  The release of thiols into the wine from yeast has been attributed to lowering reductive characteristics by being able to oxidize methanethiol and ethanethiol into their non-volatile disulfide forms (Lavigne and Dubourdieu 1996); however, this greatly depends on other factors in the aging process, and realistically should impart a more reductive character to the wine.  Yeast glycoproteins from autolysis may also decrease astringency in wines through interaction with phenolic compounds (Escot et al. 2001).  Lees autolysis can also impart sweetness to wine, which may be in part due to sweet peptide fractions released during cell autolysis.  One such fraction appears to be derived from heat shock proteins (Hsp12p) (Marchal et al. 2011), which is expressed from high temperature, ethanol, oxidative stress, and glycerol concentrations (Varela et al. 1995).  All of these factors are present under winemaking conditions (Marchal et al. 2011).  Many of these impacts of lees aging can be affected by winemaking practices, such as frequency of stirring, amount of lees present, amount of oxygen ingress, pectinase/glucosidase enzyme additions (such as Extralyse by Laffort), and perhaps even quality of lees.  This study examines the impact of one such lees stirring regime on the chemical and sensory qualities of wine.

Results and Discussion

The finished wines showed decreasing levels of residual sugar with stirring and with enzyme addition.  Some malolactic fermentation could be observed in the stirred wine with Extralyse as well.  Wine tended to become more cold stable over time, but the unstirred wine showed the highest level of cold stability but also the highest level of bentonite addition necessary to become heat stable.  This increase in heat stability agrees with results seen by Ledoux et al. 1992, but the tartrate stability decrease disagrees with results obtained by Moine-Ledoux et al. 1997.  By 10/20, the barrels had a strange aroma (lacked fruitiness), and instead was described by the winemaker as stinky, gluey, butterscotch, with a Burgundian character.  The strange aroma in this wine may have originated from Captan fungicide residue, although this has not been confirmed.

Juice Chemistry

Chemistry after Primary Fermentation

Wine Chemistry

Lab Results from Enology Analytics from Early January, 2017

Stability before and after Stirring Regimes

The wine was tasted at two different sensory sessions. At the January 25 session at Early Mountain Vineyards, no real preference trend could be observed (Table 1).  The comments made on these wines suggest a strong oak presence, especially in the stirred wines.

Lab Results from ETS from Early January, 2017

There was a strong trend for the Stirred wine to have higher Sweetness scores than the unstirred wine for the January 25 tasting session. This could correspond to the general characterization of the stirred wines as being oaky by the judges.  However, the stirred wine with Extralyse was only weakly scored as being sweeter than the unstirred wine.  In general, stirred wines had a slight tendency to have more Yeast Characteristics, more Body, and more Sweetness.

In the February 15 session at Williamsburg Winery, there was no preference for any of the kinds of stirring regimes.

No strong trends were found for the descriptors used in this study on the February 15 tasting.  No major trends could be observed in these wines as well, except that stirring tended to increase Body.

These results suggest that stirring may enhance Sweetness, Depth of Flavor, Yeast Character, and Body, although many of these effects were not strong.  The effect of Extralyse in combination with stirring was not too different than from stirring itself.  However, the stirring regime for this study was relatively short (8 weeks).  In the future, more realistic stirring regimes should be implemented to see whether differences tend to increase over time, particularly with respect to Extralyse.

Methods

7.5 tons of identically sourced Chardonnay  grapes from Silver Creek Vineyard (Glen Anne, 3 year old vines) were hand harvested on 9/15/16, chilled overnight then whole cluster pressed.    The juice received 30 ppm Sulfur dioxide and 30 mls/ton Color Pro enzyme.  Tartaric acid was added as needed to adjust the pH to 3.44.    Following cold settling (9/18) the juice was racked off of lees to 143 NTUs and inoculated with 25 g/hl CY3079 to reach a fermentation NTU of 195.  Following lag phase, when the fermentation had begun (9/20), the juice was aeratively racked with lees inclusion to barrels and an NTU of 110 in order to homogenize and aerate for barrel fermentation.  Each treatment was in 4 barrels.

Following alcoholic fermentation (10/17), barrels were stabilized with 50ppm sulfur dioxide, topped, and samples from each treatment were taken and sent off for cold stability and heat stability analysis.  Since each treatment had 4 barrels, these samples were taken by mixing equal sample volumes from each barrel belonging to a specific treatment.  On 10/20, to a trial lot of 4 barrels, 6 g/hl of Extralyse was added.   The control and trial were stirred 1 time per week with a stainless steel “baton”, using 6 to 8 strokes until the lees were back in suspension.  A set of barrels was left unstirred. The NTUs at the beginning of the stirring regime was 1097 NTU in the barrel with Extralyse, and 1085 NTU in the barrel that was stirred (ARC wanted a target of 2000-3000 NTU).  All barrels received 50 ppm SO2on 12/7.

Post-Fermentation heat and cold stability were performed by ETS.  All cold stability trials on finished wine from the second set of barrels was performed by My Enologist.  All general wine chemistry on finished wine was performed by Enology Analytics.  The rest of the results were gathered in-house.

In order to balance the data set to perform statistical descriptive analysis on the January 25 tasting, any judge who had not fully completed the descriptive analysis ratings were removed.   In order to then make the amount of judges between groups equivalent, one judge from group 1 was transferred to group 2.  This resulted in a final data set of 3 groups, each with 10 judges (considered as replications within groups, and groups were considered as assessors).  Data was analyzed using Panel Check V1.4.2.  Because this is not a truly statistical set-up, any results which are found to be statistically significant (p<0.05) will be denoted as a “strong trend” or a “strong tendency,” as opposed to general trends or tendencies.  The statistical significance here will ignore any other significant effects or interactions which may confound the results (such as a statistically significant interaction of Judge x Wine confounding a significant result from Wine alone).  The descriptors used in this study were Fruit Intensity, Yeast Character, Depth of Flavor, Sweetness, Bitterness, and Body.

The procedures for analyzing sensory analysis were the same for the February 15 tasting.  For descriptive analysis, in order to balance the data set one judge from group 1 was assigned to group 2, resulting in 3 groups each with 3 judges.

References

Chatonnet, P., Dubourdieu, D., and Boidron, J. N. 1992. Incidence des conditions de fermentation et d’èlevage des vins blancs secs en barriques sur leur composition en substances cèdèes par le bois de chêne. Sci. Aliments. 12:665–685.

Escot, S., Feuillat, M., Dulau, L., and Charpentier, C. 2001. Release of polysaccharides by yeasts and the influence of released polysaccharides on colour stability and wine astringency. Aust. J. Grape Wine Res. 7:153–159.

Lavigne, V. and Dubourdieu, D. 1996. Demonstration and interpretation of the yeast lees ability to adsorb certain volatile thiols contained in wine. J. Int. Sci. Vigne Vin. 30:201–206.

Ledoux, V., Dulau, L., and Dubourdieu, D. 1992. Interprètation de l’amèlioration de la stabilitè protèique des vins au cours de l’èlevage sur lies. J. Int. Sci. Vigne Vin. 26:239–251

Llaubères, R.-M., Dubourdieu, D., and Villettaz, J.-C. 1987. Exocellular polysaccharides from Saccharomyces in Wine. J. Sci. Food Agric. 41:277–286.

Marchal, A., Marullo, P., Moine, V., and Dubourdieu, D. 2011. Influence of yeast macromolecules on sweetness in dry wines: role of the Saccharomyces cerevisiae protein Hsp12. Journal of Agricultural and Food Chemistry. 59:2004-2010.

Moine-Ledoux, V., Perrin, A., Paladin, I., and Dubourdieu, D. 1997. Premiers rèsultats de stabilisation tartrique des vins par addition de mannoprotèines purifièes (Mannostab). J. Int. Sci. Vigne Vin. 31:23–31.

Tominaga, T., Blanchard, L., Darriet, P., and Dubourdieu, D. 2000. A powerful aromatic volatile thiol, 2-furanmethanethiol, exhibiting roast coffee aroma in wines made from several Vitis vinifera grape varieties. J. Agric. Food Chem. 48:1799–1802.

Varela, J. C. S., Praekelt, U. M., Meacock, P. A., Planta, R. J., and Mager, W. H. 1995. The Saccharomyces cerevisiae HSP12 gene is activated by the high- osmolarity glycerol pathway and negatively regulated by protein kinase A. Mol. Cell. Biol. 15:6232–6245.

The purpose of the Stabulation and Thiol Enzyme trials was to investigate the impact of increasing aromatic thiols in thiol driven varietals and winestyles. The quantitative data indicates that the treatments were able to increase the amount of the target thiol molecules in most instances.  Variables which can impact the increase of thiols include winegrape varietal, vineyard quality in terms of precursor thiol molecules, yeast selection, proper yeast rehydration, yeast nutrition for strong fermentation and process options such as Stabulation and Thiol Enzyme addition. ENose evaluation of the resulting wines shows that there are clear differences between control and treated wines.

The sensory evaluations did not always follow intuition that increases in the quality parameter of aromatic thiol molecules would result in a better perception of the resulting wines.  The confounding factors such as yeast and fermentation treatments, while bringing variation to this study, do allow for optimization in concert with a Stabulation or Thiol Enzyme treatment. Biolaffort recommends the use of specific thiol revealing yeast strains with the Thiol Enzyme application. The small size of the tasting panels, usually less than 15, can also cause some unexplainable variation in the perception aspect of the evaluation.

The Stabulation and Thiol Enzyme treatments can be unequivocally viewed as beneficial tools in a winemaker’s arsenal in dealing with either fruit limitations or driving specific wine styles including differentiation of finished wines from similar incoming fruit especially when taking the aforementioned variability factors into account.

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