Co-fermentation of Petit Verdot and Petit Manseng at King family Vineyards. Photo Credit: Matthieu Finot

Simply stated, co-fermentation as “the simultaneous fermentation of two or more varieties in the same vessel”(1). This ancient technique likely arose from a time when vineyards were interplanted with several varieties, either due to the availability of replacement vines or simply the lack of techniques to determine varietal identity. Some well known wines have traditionally been produced as co-ferments including Côte Rôtie from the Northern Rhône which usually includes 5-10% Viognier added to Syrah. Chianti Classico was historically a co-ferment of Sangiovese with the indigenous red grape Canaiolo Nero as well Trebbiano and Malvasia, both white varieties. Interplanted vineyards can also be found in the New World. Bucklin’s Old Hill Ranch vineyard, one of the oldest in California, is an interplanting of 16 varieties on 12 acres, all harvested and vinified together(2). On a recent trip to California, my husband and I visited Ridge Vineyards, whose Geyserville “Old Patch” contains vines up to 130 years old that include Zinfandel interplanted with Carignane, Petit Syrah and Mourvedre. This vineyard is picked and vinified as a co-fermented field blend with stunning results.

Winemakers use co-fermentation for many reasons. Some cite a “lifting of the aromas”, “enhanced texture”, “softening of the wine” or “improved brilliance and intensity of color”(1,3), while others, like Bucklin and Ridge, honor their terroir and history. In many cases, increased color stability is cited as a reason for co-fermentation. It is counterintuitive to add a white wine to a red to stabilize color, Roger Boulton (2001)(4) provided a chemical explanation for this approach in his work on co-pigmentation. When anthocyanins, the main pigments in red wines, are extracted from grapes, they can take on five different chemical forms, only one of which has red color(3). Anthocyanins are also subject to loss of color through the bleaching effects of SO2 or by binding with other chemical constituents, including oxygen(3). The colored form of anthocyanins is more prevalent in lower pH wines, and can be stabilized by association with other anthocyanins or other phenolics in the wine. These other phenolics, referred to as co-pigments, form weakly bonded stacks of flat molecules, sandwiching the anthocyanins in a way that that protects them from bleaching, and may increase the likelihood of forming long-term bonds with tannins, further stabilizing color. Co-pigmented anthocyanins take on a slightly bluer form, leading to the purple tones found in young red wines. Boulton (2001) hypothesized that some varieties have more co-pigments than others, and, in red wines with poor color stability, color could be enhanced by addition of co-pigments)3,4).

from  https://www.buckzin.com

When tested directly, though, co-fermentation has variable effect on color, as reviewed by Casassa et al (2012)(5). Gigliotti found increased color in one-year old Sangiovese wine co-fermented with Trebbiano and Malvasia. The same was not the case for co-fermentation of Tempranilo with Viura (a Spanish white variety) studied by Etaio et al. In a study of co-fermentation of Syrah with 5, 10, and 20% Viognier, Casassa et al (2012) found that addition of 10 and 20% Viognier led to wine with lower color measurements. Both Syrah and Viognier were measured to have the same amount of skin and seed tannins, and there were no differences in tannins in the finished wines(5). So it seems that co-fermentation may lead to color enhancement or color dilution, depending on the circumstances.

Co-fermentation of hybrid grapes with Vitis vinifera varieties is even more complicated. Hybrid grapes contain on average 1.8 times lower levels of tannin than vinifera grapes, as well as higher levels of protein in pulp cells and higher levels of pectin in skin cells(6). During fermentation, tannins bind to these proteins and pectins and are removed, leading to a 5-fold difference in tannin in the finished wine6. Norton et al (2017) studied co-fermentation of a high tannin, low protein Vinifera variety, Cabernet Sauvignon, with a low tannin, high protein hybrid variety, Marquette. They found that finished Cabernet Sauvignon wine had five times the tannin concentration of the finished Marquette wine, with three times less protein. When co-fermentations included a high proportion of Marquette, tannin concentrations were significantly lower than calculated due to dilution alone, indicating that protein and tannin are binding during fermentation and reducing the overall tannin concentration. Based on this result, they suggest blending post-fermentation may be a better approach for tannin enhancement of hybrids(7).

So in the end, it is difficult to predict the outcome of co-fermentation. The best approach is to try it on a pilot scale and carefully observe the results. When considering co-fermentation in your own winery, there are a few practical considerations to keep in mind:

• Co-fermentation can include addition of whole fruit or addition of pressed skins.
• Varieties to be co-fermented must be ripe at the same time.
• If pressed skins need to be held for any period of time, adequate refrigeration, SO₂, chitosan, and/or non-Saccharomyces yeast call be useful tools to prevent oxidation and microbial spoilage.

References

(1) Robinson, J. The Oxford Companion to Wine, 3rd Edition.; Oxford University Press: Oxford, 2006.

(2) Bucklin, W. Vineyard Map. Bucklin Old Hill Ranch.

(3) Jackson, R. S. Wine Science: Principles and Applications, 4th Edition.; Academic Press: Amsterdam, 2014.

(4) Boulton, R. The Copigmentation of Anthocyanins and Its Role in the Color of Red Wine: A Critical Review. Am J Enol Vitic. 2001, 52 (2), 67–87.

(5) Casassa, L. F.; Keirsey, L. S.; Mireles, M. S.; Harbertson, J. F. Cofermentation of Syrah with Viognier: Evolution of Color and Phenolics during Winemaking and Bottle Aging. Am J Enol Vitic. 2012, 63 (4), 538–543. 

(6) Springer, L. F.; Sacks, G. Protein-Precipitable Tannin in Wines from Vitis Vinifera and Interspecific Hybrid Grapes (Vitis Sp.): Differences in Concentration, Extract- Ability, and Cell Wall Binding. Journal of Agricultural and Food Chemistry 62, 7515–7523.

(7) Norton, E. L.; Sacks, G. L.; Talbert, J. N. Nonlinear Behavior of Protein and Tannin in Wine Produced by Cofermentation of an Interspecific Hybrid (Vitis Spp.) and Vinifera Cultivar. Am J Enol Vitic. 2020, 71 (1), 26–32. 

In April of 2020, the WRE hosted a virtual panel discussion with three winemakers to discuss co-fermentation experiments from the 2019 vintage. Michael Heny (Michael Shaps Wineworks) used pressed Viognier skins to increase fruitiness and volume in a Chambourcin fermentation. Doug Fabbioli (Fabbioli Cellars) tested the effects of both Vidal skins and Merlot pressings during co-fermentation with Chambourcin. Matthieu Finot (King Family Vineyards) co-fermented Petit Manseng with Petit Verdot as a pilot for a potential field pick.

Watch Video Here

Summary

The purpose of this experiment was to explore the chemical and sensory effects of the co-fermentation of Chambourcin with Viognier pomace. Final chemistry, phenolics and sensory properties were compared for two treatments: 100 % Chambourcin and 80% Chambourcin/20% Viognier skins. Addition of Viognier skins to Chambourcin fermentation had an immediate impact on the chemistry of the juice, lowering the TA and increasing the pH. The cofermentation bin produced the same yield as the bin with only Chambourcin, indicating a substantial increase in yield from Viognier skins. The co-fermented wine had much lower color intensity and total anthocyanins than the control wine, but higher concentrations of other phenolics including catechin (seed tannin) and total tannins. A panel of four winemakers tasting the wines blind noted that the co-fermented wine did not balance well, less like a red wine, more rustic, potentially with some reduction.

Introduction

            The purpose of this experiment was to explore the chemical and sensory effects of the co-fermentation of Chambourcin with Viognier pomace. With thick skins and expressive flavors, Viognier has been an integral part of Virginia wine production since the early 1990’s. However, the same thick skins that make it more resistant to fungal pressure than some other Vinifera varieties also makes it more difficult to extract the juice from the berry. Producers typically see up to 50 liters per ton lower yield than with other white wine varieties. This study aims to find a synergistic use for Viognier pomace, an otherwise discarded raw material, with Chambourcin, the most widely planted red hybrid grape in the state¹.

Winemakers use co-fermentation for many reasons. Some cite a “lifting of the aromas”, “enhanced texture”, “softening of the wine” or “improved brilliance and intensity of color”^1,2. Previous published studies have found varying results when examining the effects of co-fermentation. One study found color enhancement when Sangiovese was co-fermented with Malvasia and Trebbiano while another found color was diluted in a co-fermentation of Syrah with Viognier⁵. Neither of these studies examined sensory aspects, however. In a previous WRE study in 2015, Emily Pelton from Veritas Vineyard and Winery found lower color when Cabernet Franc was co-fermented with 6% Viognier pomace. These wines were significantly different, with a preference for the control (100% Cabernet Franc) wine. In 2017, Milt and Sandy McPherson from Hunting Creek Vineyards co-fermented Petit Verdot with 10% Viognier pomace. In this trial, color was also lower in the co-fermented wines, but there were no sensory differences.

Several considerations led to the co-fermentation of Chambourcin with pressed Viognier skins:

1. As an inter-specific hybrid, Chambourcin is expected to have lower tannin than Vitis vinifera species⁵, so unlike tannic varieties like Petit Verdot or Cabernet Franc, it is possible Chambourcin may gain phenolics from the addition of Viognier.
2. Chambourcin sometimes has an off-putting acidity. Co-fermentation with skins from a high pH white grape variety may help temper the acidity of the Chambourcin.
3. One of the Chambourcin-based red table blends produced at Michael Shaps Wineworks already includes Viognier as part of the blend. Co-fermentation may offer the opportunity to better integrate those flavors. 
4. Many East Coast wineries produce varietal Chambourcin wines. In a time when we are looking for ways to grow varieties that are tolerant to Virginia terroir (i.e. rain), Chambourcin shows promise. However, varietal Chambourcin wines can lack the complexity and phenolic structure desired in fine red wines. Identification of winemaking procedures to improve the sensory characters of Chambourcin could have a significant impact on acceptance and marketability of wine made from this grape variety. Co-fermentation with other varieties is one potential approach.
5. In this study, final chemistry, phenolics and sensory properties were compared for two treatments: 100 % Chambourcin and 80% Chambourcin/20% Viognier skins.

Methods

Viognier was pressed the day before Chambourcin processing. Pomace was collected at the time of pressing, sparged with CO₂ gas, covered with plastic wrap, and stored in a refrigerated room overnight until use in co-fermentation. Chambourcin was hand harvested and refrigerated overnight. The following day, macrobins were randomized for processing and destemmed into TBins. One bin received 1639 pounds of Chambourcin while the other received 1288 pounds of Charbourcin and 350 pounds of Viognier skins. Both bins were totaled 0.8 tons. All other additions and cellar operations were the same among bins. Each fermentation received 30 ppm SO₂ and 0.1 mL/L Scottzyme Color Pro at destemming. Fermentations were inoculated with 0.25 g/L ICV GRE (Scottlabs) rehydrated in 0.15 g/L GoFerm. Fermentations were punched down twice per day and monitored daily for Brix and temperature. Superfood (0.6 g/L) and DAP (0.18 g/L) were added at 1/3 Brix depletion. Fermentations were pressed on the same day, at the completion of Brix depletion. Volume after pressing was recorded for yield calculation. Wine settled for 2 days prior to racking and transfer to comparable barrels. Malic acid depletion was monitored in barrel until completion and addition of 50 ppm SO₂.

Due to restrictions put in place during the COVID-19 pandemic, group sensory analysis was not done on these wines. However, four winemakers tasted the wines blind and wrote open ended notes. A panel discussion was recorded; the full video can be found on the WRE YouTube channel.

Results/Discussion

The addition of Viognier skins to the Chambourcin fermentation had an immediate impact on the chemistry of the juice (Table 1), lowering the TA and increasing the pH considerably. This is likely due to an increase in the proportion of potassium coming from the skins of Viognier. Fermentation proceeded quickly at high temperature, with little difference in kinetics between the two lots (Figure 1). The pH difference seen in the juice persisted in the finished wine chemistry (Tables 2, 3), which also shows lower titratable acidity in the co-fermented wine. Differences in lactic acid between the two wines likely reflects differences in initial malic acid between Chambourcin and Viognier. The co-fermented wine had higher potassium, a result consistent with the addition of skins and the pH effect already observed.

Each bin received the same overall weight of grapes, and each treatment had the same yield after pressing (Table 4). This indicates that co-fermentation on pressed skins succeeded in extracting much more volume from the Viognier skins than pressing alone. It is surprising this volume was equal to that of fresh fruit, indicating this may be an economical way to utilize this otherwise wasted resource and augment volumes in Chambourcin.

The co-fermented wine had much lower color intensity and total anthocyanins than the control wine (Figure 2, Table 5). There is approximately 20% reduction in anthocyanins, indicating dilution in direct proportion to the addition of white grapes. The difference in color, however, is considerably larger. Color is affected by many factors, including pH. Anthocyanins are more likely to be found in their colored form at lower pH. The control wine has notably lower pH and much higher color expression. 

With the exception of anthocyanins, co-fermentation of Chambourcin with Viognier appeared to increase other phenolics (Table 5); both catechin (seed tannin) and total tannins were higher in the co-fermented wine. There is little difference in phenolic content between red wine skins and white wine skins, with anthocyanins the sole exception. Instead, the difference is in the winemaking, with little skin contact time and limited extraction of phenolics in white wines vs. red wines⁶. In their study of co-fermentation of Viognier with Syrah, Casassa et al (2012) measured total skin and seed tannins in both varieties and found they were nearly the same⁴. Hybrid grapes, on the other hand, are known to contain lower levels of tannin (as much as five times less) as well as higher levels of protein that may remove tannin during fermentation^5,7. In this case, addition of Vinifera to Chambourcin improved the proportion of extractable tannin available during fermentation, potentially leading to more structure in the finished wine. 

Based on comments from four winemakers who tasted these wines blind, this Chambourcin was very concentrated with deep color, rich, ripe aromatics of raspberry and cranberry and noticeable acidity. The co-fermented wine was described as fruity with floral and sweet citrus aromas, black raspberry flavors and softer structure. Several winemakers noted that the co-fermented wine did not balance well, less like a red wine, more rustic, potentially with some reduction. One also noted bitterness, which may be a biproduct of added pomace contact.

Table 1: Primary juice chemistry for two treatments of Chambourcin (in-house data)

Figure 1: Fermentation kinetics for two treatments of Chambourcin (in-house data)

Table 2: Post-malolactic fermentation chemistry for two treatments of Chambourcin (in-house data)

Table 3: Wine chemistry for two treatments of Chambourcin (ICVLabs, March 2020)

Table 4: Yield for two treatments of Chambourcin (in-house data)

Figure 2: Color Intensity for two treatments of Chambourcin (ICVLabs, March 2020)

Table 5: Phenolic analysis for two treatments of Chambourcin (mg/L) (ETSLabs March 2020)

References

(1) Wood, V.; Custer, S.; Watson, K.; Alper, D. Virginia 2018 Commercial Grape Report. 11.

(2) Robinson, J. The Oxford Companion to Wine, 3^rd Edition.; Oxford University Press: Oxford, 2006.

(3) Jackson, R. S. Wine Science: Principles and Applications, 4^th Edition.; Academic Press: Amsterdam, 2014.

(4) Casassa, L. F.; Keirsey, L. S.; Mireles, M. S.; Harbertson, J. F. Cofermentation of Syrah with Viognier: Evolution of Color and Phenolics during Winemaking and Bottle Aging. Am J Enol Vitic. 2012, 63 (4), 538–543. 

(5) Springer, L. F.; Sacks, G. Protein-Precipitable Tannin in Wines from Vitis Vinifera and Interspecific Hybrid Grapes (Vitis Sp.): Differences in Concentration, Extract- Ability, and Cell Wall Binding. Journal of Agricultural and Food Chemistry 62, 7515–7523.

(6) Price, S. F. Phenolic Analysis in White Wines and Juices at ETS Laboratories; Geneva, New York, 2006.

(7) Norton, E. L.; Sacks, G. L.; Talbert, J. N. Nonlinear Behavior of Protein and Tannin in Wine Produced by Cofermentation of an Interspecific Hybrid (Vitis Sp.) and Vinifera Cultivar. Am J Enol Vitic. 2020, 71 (1), 26–32.

Summary

The purpose of this experiment was to explore the chemical and sensory effects of the co-fermentation of Chambourcin with pomace from Vidal and Merlot. In three separate fermentations, Chambourcin was fermented alone, with 15% Vidal pomace and with 15% Merlot pomace. Co-fermentation lowered pH in both cases. Co-fermentation of Chambourcin with Vidal led to higher color measures, but not higher anthocyanins. This wine was described as bright with berry aromas and noticeable acidity. Co-fermentation with Merlot pomace led to wine with less color but higher tannin concentration and perceived tannin structure. A panel of four judges indicated the wines were different but had no consensus favorite.

Introduction

The purpose of this experiment was to explore the chemical and sensory effects of the co-fermentation of Chambourcin with pomace from Vidal and Merlot. Chambourcin, a French-American hybrid variety, is relatively resilient to the wet growing conditions that can occur in Virginia. After the 2018 vintage, there was a renewed discussion around growing varieties that are tolerant to this aspect of our terroir (i.e. rain). However, varietal Chambourcin wines often lack the complexity and phenolic structure desired in fine red wines. Hybrid wines can have as much as five times lower concentration of tannins than Vinifera wines made with comparable winemaking techniques¹. In general, phenolic composition and color, along with polysaccharides, have been shown to be primary drivers of perceived wine quality². These characteristics have also been correlated with consumer liking and bottle price in red wines². Identification of winemaking procedures to improve the sensory characters of Chambourcin could have a significant impact on acceptance and marketability of wine made from this grape variety. Co-fermentation with other varieties is one potential approach.

Winemakers use co-fermentation for many reasons. Some cite a “lifting of the aromas”, “enhanced texture”, “softening of the wine” or “improved brilliance and intensity of color”^1,2. Previous published studies have found varying results when examining the effects of co-fermentation. One study found color enhancement when Sangiovese was co-fermented with Malvasia and Trebbiano while another found color was diluted in a co-fermentation of Syrah with Viognier⁵. Neither of these studies examined sensory aspects, however. In a previous WRE study in 2015, Emily Pelton from Veritas Vineyard and Winery found lower color when Cabernet Franc was co-fermented with 6% Viognier pomace. These wines were significantly different, with a preference for the control (100% Cabernet Franc) wine. In 2017, Milt and Sandy McPherson from Hunting Creek Vineyards co-fermented Petit Verdot with 10% Viognier pomace. In this trial, color was also lower in the co-fermented wines, but there were no sensory differences.

In this study, Chambourcin was fermented three ways:

• 100% Chambourcin
• 85% Chambourcin, 15% Vidal pomace
• 85% Chambourcin, 15% Merlot pomace

When pressed, Vidal pomace often contains notable residual pulp. Additional flavor could be extracted from these skins during a red wine fermentation, leading to a lifting of the sensory characteristics and production of a lighter, fruitier wine. Merlot pomace was thought to have the potential to convey higher tannin to the wine, producing a more structured expression.

Methods

Vidal was pressed on 9/17/19, two days prior to Chambourcin processing. Pomace was collected and SO₂ was drizzled over the top to protect against oxidation and microbial spoilage. This pomace was stored in a cool cellar until use. Merlot was pressed on the same day as destemming for co-fermentation and therefore received no additional processing.

Macrobins were randomized at the time of Chambourcin processing. Grapes were destemmed and crushed into three bins: 

1. Control (100% Chambourcin)
2. Vidal Co-ferment (85% Chambourcin, 15% Vidal pomace)
3. Merlot co-ferment (85% Chambourcin, 15% Merlot pomace)

Each bin contained 0.8 ton total weight of fruit after the addition of skins.  For both Vidal Blanc and Merlot treatments, 225 lbs of pomace were added. All other additions and cellar operations were the same among bins. Each fermentation received 25 ppm SO_2, 1 lb/ton Med Plus French oak chips, and 100 ml/ton Color X. Bins were inoculated with D80 yeast rehydrated in GoFerm. Fermentations were punched down twice per day and monitored daily for Brix and temperature. VP41 malic acid bacteria was added after Brix depletion, prior to pressing (on 9/24). All three bins were pressed on 9/26, at the completion of alcoholic fermentation. Wine was settled for two days then racked to comparable barrels. After the completion of malolactic fermentation, wine was racked and returned to barrel with the addition of 55 ppm SO₂.

Due to restrictions put in place during the COVID-19 pandemic, group sensory analysis was not done on these wines. However, four winemakers tasted the wines blind with randomly assigned codes and wrote open ended notes followed by a recorded panel discussion of the sensory properties of the wines. The full discussion can be found on the WRE YouTube channel.

Results

Chambourcin fruit measured 21.6° Brix with a pH = 3.42 at harvest. Vidal used for co-fermentation measured 21.6 ° Brix with a pH = 3.67. Fermentation kinetics were faster and warmer for the co-fermentation with Merlot skins, likely due to a higher initial inoculant of yeast from previously fermented Merlot (Figure 1). This fermentation also reached the highest temperature. The Vidal co-fermentation had the lowest overall temperature, never rising above 72°F though the fermentation kept pace with the control. 

The pH of the finished wine was lower in both co-fermentations than in the control (Table 1). Color intensity was higher for the Vidal co-fermentation than the other treatments (Table 2). Color can be influenced by pH (higher at lower pH) and SO₂ levels. Free SO₂ was within 4ppm for all treatments at the time of color measurement (data not shown). The pH in the Vidal co-ferment was lower, which may have contributed to higher color. However, pH of the Merlot was also lower than control without this color enhancement effect, indicating other factors may be contributing. In some co-fermentations with white wine, cofactors from the white variety help stabilize color to prevent SO₂ bleaching and oxidative loss⁵. This effect is variable and dependent on relative cofactor concentration in each variety but may be the mechanism leading to higher color intensity in the Chamboucin-Vidal conferment. The wine did not have higher anthocyanins overall (Table 3), further implicating co-pigmentation.

Co-fermentation with Merlot pomace lowered anthocyanins considerably (Table 3) relative to control, also lowering color intensity (Table 2). Most of the available anthocyanins in Merlot skins were likely extracted in the initial fermentation (anthocyanins are usually extracted within the first 6 days of fermentation⁶) and thus the addition of Merlot pomace may have diluted the concentration of extractable anthocyanins in the bin. Catechin and tannins, however, were notably higher in this wine. Though anthocyanins are quickly released, other phenolics continue to extract over time (at least 40 days) when in contact with ethanol⁶. Seed phenolics like catechin are not available until the waxy cuticle has been weakened by ethanol⁷ and were also likely still intact after the first fermentation. When ethanol from the co-fermentation began to build, cell walls were already weakened and extraction of phenolics could continue where they left off in the first fermentation. 

In a panel discussion of four winemakers who tasted the wines blind, the Chambourcin only wine was noted as a good, fruity, easy drinking wine with varietal character, soft tannins and magenta/purple color. The Chambourcin/Vidal co-fermented wine was noted to be bright with berry aromas, but with an acidity that some liked and others did not. The Chambourcin/Merlot co-ferment was noted by one winemaker to have riper fruit character, and all of the winemakers noted this wine had more perceived tannic structure. There was no consensus on a preferred wine, but comments during discussion indicate the three wines had sensory differences.

Figure 1: Fermentation kinetics for three treatments of Chambourcin (in-house data)

Table 1: Finished wine chemistry for three treatments of Chambourcin (ICV Labs)

Table 2: Color metrics for three treatments of Chambourcin (ICV Labs)

Table 3: Phenolic analysis for three treatments of Chambourcin (mg/L) (ICV Labs)

References

(1) Springer, L. F.; Sacks, G. Protein-Precipitable Tannin in Wines from Vitis Vinifera and Interspecific Hybrid Grapes (Vitis Ssp.): Differences in Concentration, Extract- Ability, and Cell Wall Binding. Journal of Agricultural and Food Chemistry 62, 7515–7523.

(2) Fanzone, M.; Peña-Neira, A.; Gil, M.; Jofré, V.; Assof, M.; Zamora, F. Impact of Phenolic and Polysaccharidic Composition on Commercial Value of Argentinean Malbec and Cabernet Sauvignon Wines. Food Research International 2012, 45 (1), 402–414. 

(3) Robinson, J. The Oxford Companion to Wine, 3^rd Edition.; Oxford University Press: Oxford, 2006.

(4) Jackson, R. S. Wine Science: Principles and Applications, 4^th Edition.; Academic Press: Amsterdam, 2014.

(5) Casassa, L. F.; Keirsey, L. S.; Mireles, M. S.; Harbertson, J. F. Cofermentation of Syrah with Viognier: Evolution of Color and Phenolics during Winemaking and Bottle Aging. Am J Enol Vitic. 2012, 63 (4), 538–543. 

(6) Ribereau-Gayon, P.; Dubourdieu, D.; Doneche, B.; Lonvaud, A. Handbook of Enology Volume 1: The Microbiology of Wine and Vinifications, 2nd ed.; John Wiley & Sons: West Sussex, England, 2006.

(7)        Razungles, A. Extraction Technologies and Wine Quality. In Managing Wine Quality: Volume 2 – oenology and wine quality; Woodhead Publishing: Cambridge, 2010; Vol. 2.

Summary

The purpose of this experiment was to explore the chemical and sensory effects of co-fermenting Petit Verdot with Petit Manseng. Chemical and sensory characteristics of a co-fermentation using 75% Petit Verdot/25% Petit Manseng were compared to those from a fermentation of 100% Petit Verdot. The co-fermented wine had higher alcohol (despite very similar starting Brix), higher potassium, slightly higher pH, and notably lower color intensity. Anthocyanin concentrations were also lower in the co-fermented wine. Other phenolic measurements were largely the same, with the co-fermented wine having only 7% lower tannin than the control wine. In a blind tasting by four winemakers, the Petit Verdot was described as a dark, concentrated, structured wine with very positive and classic descriptors for varietal character. The co-fermented wine was noted as very different from the Petit Verdot with descriptors including tropical, citrus, floral aromas and noticeably lighter color. The mouthfeel was described as “bright”, “rounder but with length and sweetness”, but also “grippy”, with “more tannin perception”.

Introduction

The purpose of this experiment was to explore the chemical and sensory effects of co-fermenting Petit Verdot with Petit Manseng. Co-fermentation is “the simultaneous fermentation of two or more varieties in the same vessel”¹. This ancient technique likely arose from a time when vineyards were interplanted with several varieties, either due to the availability of replacement vines or simply the lack of techniques to determine varietal identity. Some well-known wines have traditionally been produced as co-ferments including Côte Rôtie from the Northern Rhône which usually includes 5-10% Viognier added to Syrah. Chianti Classico was historically a co-ferment of Sangiovese with the indigenous red grape Canaiolo Nero as well Trebbiano and Malvasia, both white varieties. Interplanted vineyards can also be found in the New World. Bucklin’s Old Hill Ranch vineyard, one of the oldest in California, is an interplanting of 16 varieties on 12 acres, all harvested and vinified together². Ridge Vineyards Geyserville “Old Patch” contains vines up to 130 years old that include Zinfandel interplanted with Carignane, Petit Syrah and Mourvedre. This vineyard is picked and vinified as a co-fermented field blend with stunning results.

Winemakers use co-fermentation for many reasons. Some cite a “lifting of the aromas”, “enhanced texture”, “softening of the wine” or “improved brilliance and intensity of color”^1,3, while others, like Bucklin and Ridge, honor their terroir and history. Co-fermenting Petit Verdot and Petit Manseng stems from several factors:

1. Petit Verdot is a dark fruited red variety with poor acidity, likely due to high potassium load in the skins.
2. Petit Manseng is a high acid, high Brix white variety that is ripe around the same time as Petit Verdot.
3. The Petit Verdot block of the Crown Orchard in Batesville, Virginia contains four short rows of Petit Manseng. Though this was not the Petit Manseng used in this trial, it presents a possible co-harvest in the future.

In this trial, the chemical, phenolic and sensory characteristics of a co-fermentation using 75% Petit Verdot/25% Petit Manseng are compared to those from a fermentation of 100% Petit Verdot.

Methods

Petit Manseng and Petit Verdot grapes were hand harvested on the same day (9/23) and chilled overnight. Grapes were destemmed to 1.5 ton Bins the following day with the addition of 15ppm SO₂. Grapes were loaded into bins according to weight, with the treatment bin receiving 75% Petit Verdot and 25% Petit Manseng by weight (Figure 1). The control bin received 100% Petit Verdot. The following day (9/26), bins were inoculated with 12 g/hL D254 yeast (Scottlabs). Fermentations were punched down twice per day and monitored daily for Brix and temperature. Tartaric acid (1 g/L) was added after fermentation, before pressing (on 10/10). Both bins were pressed the same day (10/11) after 7 days of extended maceration. Wine was allowed to settle for 1-2 days prior to racking and transfer to identical barrels. Malolactic conversion occurred naturally in barrel. At the completion of malolactic fermentation, 3 g/hL Stab Micro (Enartis), 2 g/L tartaric acid, and 66ppm SO₂ were added to each barrel. Due to restrictions put in place during the COVID-19 pandemic, group sensory analysis was not done on these wines. However, four winemakers tasted the wines blind and wrote open ended notes, followed by a panel discussion of the wines. The full recording of this panel discussion can be found on the WRE YouTube channel.

Results

Initial juice chemistry shows very similar sugar levels with slightly lower pH for the co-ferment (Table 1). The control wine fermented faster and finished earlier than the co-fermented wine. The cap on the control wine had dropped by the time both bins were pressed while the co-fermented wine still had an intact cap when pressed (Matthieu Finot, personal communication).

Figure 1: Petit Verdot and Petit Manseng grapes were destemmed into the same TBin for co-fermentation (photo by Matthieu Finot)

Table 1: Red fruit chemistry after crush for two treatments of Petit Verdot (in-house lab)

The co-fermented wine had higher alcohol, consistent with slower (cooler) fermentation, as well as higher potassium and slightly higher pH (Table 2). Though Petit Verdot is thought to contain high levels of potassium that contribute to its high pH, Petit Manseng may also have high potassium. Petit Manseng has very small berries, leading to a high skin:pulp ratio. The drop in acidity often attributed to high potassium is not seen as often in Petit Manseng white wines due to limited if any skin contact in wines made from this variety. However, in a WRE experiment testing skin fermentation of Petit Manseng in 2018, Emily Pelton found finished Petit Manseng wine with pH values of 4.1 and 4.2. Addition of Petit Manseng to red wine fermentations, therefore, may not help acidity but rather have a detrimental effect on this parameter.

Table 2: General wine chemistry for two treatments of Petit Verdot (ICV labs)

The co-fermented wine also had notably lower color intensity (Figure 2), with a hue of 0.80 compared to a hue of 0.70 in the control wine. Higher hue indicates a shift toward the yellow portion of the spectrum, away from the red. The difference in color intensity is likely due to dilution of anthocyanins, as seen in values for all categories of anthocyanins measured (Table 3). Though anthocyanins showed large differences, other phenolic measurements were largely the same (Table 4), with the co-fermented wine having only 7% lower tannin than the control wine.

In a blind tasting by four winemakers, the Petit Verdot was described as a dark, concentrated, structured wine with very positive and classic descriptors for varietal character. The co-fermented wine was noted as very different. Descriptors include tropical, citrus, floral aromas and noticeably lighter color. The mouthfeel was described as “bright”, “rounder but with length and sweetness”, but also “grippy”, with “more tannin perception”. This was a higher alcohol wine, and one winemaker remarked the alcohol was more apparent in the co-ferment.

Figure 2: Color intensity for two treatments of Petit Verdot (ICV labs)

Table 3: Anthocyanins for two treatments of Petit Verdot (mg/L) (ETS Labs)

Table 4: Phenolics for two treatments of Petit Verdot (mg/L) (ETS Labs)

References

(1) Robinson, J. The Oxford Companion to Wine, Third Edition.; Oxford University Press: Oxford, 2006.

(2) Bucklin, W. Vineyard Map. Bucklin Old Hill Ranch.

(3) Jackson, R. S. Wine Science: Principles and Applications, 4^th Edition.; Academic Press: Amsterdam, 2014.

In February of 2021, winemakers from across Virginia met to taste/discuss the results of two experiments focused on co-fermentation. Phil Ponton (Oakencroft Vineyards) co-fermented Chambourcin and Vidal to attain lift and fruitiness. Michael Heny (Michael Shaps Wineworks) co-fermented pressed Viognier skins in search of color stability and copigmentation.

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