Loss of Pinot Noir Color and Polymeric Pigment

Wine quality is determined by many different sensory attributes including aroma, taste and mouthfeel. For red wines, color is an additional sensory attribute that plays a significant role in perceived quality.13 This is particularly true for lighter colored red wines such as Pinot Noir. Because of this, a large amount of research has been conducted to understand factors that impact red wine color so that viticultural or winemaking practices can be modified to improve it. Red wine color primarily results when anthocyanins present in the skins of red grapes are extracted while the skins remain in contact with the fermenting juice.9

Color at 520nm (left) and polymeric pigment (right) of Pinot Noir wine with restoration of acetaldehyde (A) and/or pyruvic acid (P) after malolactic fermentation at bottling (day zero) and 90 days after bottling.

However, the color of a red wine is not solely determined by the concentration of anthocycanins. Following extraction, anthocyanins can react with a number of other compounds present in wine to form more complex color compounds. For example, anthocyanins can react with tannins to form polymeric pigments. The formation of polymeric pigments can be accelerated through reactions with acetaldehyde that result via ethyl-linked bridges between anthocyanins and tannins.5

Stable anthocyanin-derived pigments also can be formed through reactions with pyruvic acid and acetaldehyde to form vitisin A and vitisin B, respectively.3,8 All of these pigments are more resistant to oxidation and bleaching by sulfur dioxide (SO2) than individual anthocyanins and tend to increase as a wine matures, accounting for the majority of color in older wines.18

Impact of microorganisms on red wine color A number of viticultural and winemaking practices have been demonstrated to impact the formation of polymeric pigments such as increased fermentation temperature,17 extended maceration20 and saignée.10 In addition, a number of studies have reported that yeast can impact color through the adsorption of anthocyanins to their cell walls12,15 or through production of acetaldehyde and pyruvic acid.11,14

For example, Antonio Morata reported yeast strains that produced higher concentrations of acetaldehyde resulted in wines with increased vitisin B,14 a compound that can play an important role in red wine color.2 In addition to yeast, other microorganisms may play a role in red wine color development, as the concentration of compounds like pyruvic acid and acetaldehyde do not remain stable during a wine’s life. In particular, Oenococcus oeni is known to degrade acetaldehyde and pyruvic acid during malolactic fermentation (MLF).16,19

MLF and red wine color Anecdotally, winemakers have reported a decrease in red wine color post-MLF. While some of this observed color loss is undoubtedly due to the increase in pH that occurs as a result of MLF, additional impacts of O. oeni on red wine color have not been well studied. Some recent studies have reported that MLF can impact the color of Shiraz1 and Cabernet Sauvignon6 wines, but the underlying cause for the color loss was not noted. Therefore, a study to better understand the impact of MLF on red wine color was conducted.4

References

1. Abrahamse, C.E. and E.J. Bartowsky. 2012 “Timing of malolactic fermentation inoculation in Shiraz grape must and wine: influence on chemical composition.” World J. Microbiol. Biotech. 28: 255-265. 2. Alcalde-Eon, C., E. Boido, F. Carrau, E. Dellacassa and J.C. Rivas-Gonzalo. 2006 “Pigment profiles in monovarietal wines produced in Uruguay.” Am. J. Enol. Vitic. 57: 449-459. 3. Bakker, J., and C.F. Timberlake. 1997 “Isolation, identification and characterization of new color-stable anthocyanins occurring in some red wines.” J. Ag. Food Chem. 45: 35-43. 4. Burns, T.R., and J.P. Osborne. 2013 “Impact of malolactic fermentation on the color of Pinot noir and Merlot wine.” Am. J. Enol. Vitic. 64: 370-377. 5. Burns, T.R., and J.P. Osborne. 2015 “Investigating the loss of Pinot noir wine color and polymeric pigment due to malolactic fermentation and possible mechanisms.” Am. J. Enol. Vitic. 66. 130-13. 6. Costello, P.J., I.L. Francis and E.J. Bartowsky. 2012 “Variations in the effect of malolactic fermentation on the chemical and sensory properties of Cabernet sauvignon wine: interactive influences of Oenococcus oeni strain and wine matrix composition.” Aust. J. Grape Wine Res. 18: 287-301. 7. Escribano-Bailon, T., M. Alvarez-Garcia, J.C. Rivas-Gonzalo, F.J. Heredia and C. Santos-Buelga. 2001 “Color and stability of pigments derived from acetaldehyde-mediated condensation between malvidin-3-O-glucoside and (+)-catechin.” J. Agric. Food Chem. 49: 1213-1217. 8. Fulcrand, H., C. Benabdeljalil, J. Rigaud, V. Cheynier and M.A. Moutounet. 1998 “A new class of wine pigments generated by reaction between pyruvic acid and grape anthocyanins. Phyto. 47: 1401-1407. 9. Fulcrand, H., M. Duenas, E. Salas and V. Cheynier. 2006 “Phenolic reactions during winemaking and aging.” Am. J. Enol. Vitic. 57: 289-297. 10. Harbertson, J.F., M.S. Mireles, E.D. Harwood, K.M. Weller and C.F. Ross. 2009 “Chemical and sensory effects of saignee, water addition, and extended maceration on high brix must.” Am. J. Enol. Vitic. 60: 450-460. 11. Hayasaka, Y., M. Birse, J. Eglinton and M. Herderich. 2007 “The effect of Saccharomyces cerevisiae and Saccharomyces bayanus yeast on colour properties and pigment profiles of Cabernet sauvignon red wine.” Aust. J. Grape Wine Res. 13: 176-185. 12. Medina, K., E. Boido, E. Dellacassa and F. Carrau. 2005 “Yeast interactions with anthocyanins during red wine fermentation.” Am. J. Enol. Vitic. 56: 104-109. 13. Mercurio, M.D., R.G. Dambergs, D. Cozzolino, M.J. Herderich and P.A. Smith. 2010 “Relationship between red wine grades and phenolics. 1. Tannin and total phenolics concentrations.” J. Ag. Food Chem. 58: 12313-12319. 14. Morata, A., M.C. Gomez-Cordoves, B. Colomo and J.A. Suarez. 2003 “Pyruvic acid and acetaldehyde production by different strains of Saccharomyces: Relationship with vitisin A and B formation in red wines.” J. Agric. Food Chem. 51: 7402-7409. 15. Morata, A., M.C. Gomez-Cordoves B. Colomo and J.A. Suarez. 2005 “Cell wall anthocyanin adsorption by different Saccharomyces strains during the fermentation of Vitis vinifera L. cv Graciano grapes.” Eur. Food Res. Technol. 220: 341-346. 16. Osborne, J.P., R. Mira de Orduña, G.J. Pilone and S.-Q. Liu. 2000 “Acetaldehyde metabolism by wine lactic acid bacteria.” FEMS Microbiol. Lett. 191: 51-55. 17. Reynolds, A.G., M. Cliff, B. Girard and T.G. Kopp. 2001 “Influence of fermentation temperature on composition and sensory properties of Semillon and Shiraz wines.” Am. J. Enol. Vitic. 52: 235-240. 18. Salas, E., H. Fulcrand, E. Meude and V. Cheynier. 2003 “Reaction of anthocyanin and tannins in model solutions.” J. Agric. Food Chem. 51: 7951–7961. 19. Wells, A., and J.P. Osborne. 2012 “Impact of acetaldehyde and pyruvic acid bound sulfur dioxide on wine lactic acid bacteria.” L. Appli. Microbiol. 54: 187-194. 20. Zimman, A., S. Joslin, M.L. Lyon, J. Meier and A.L. Waterhouse. 2002 “Maceration variables affecting phenolic composition in commercial-scale Cabernet sauvignon winemaking trials.” Am. J. Enol. Vitic. 53: 93-98. 21. Zuehlke, J.M., and C.G. Edwards. 2013 “Impact of sulfur dioxide and temperature on culturability and viability of Brettanomyces bruxellensis in wine.” J. Food Protec. 76: 2024-2030.

Pinot Noir wines were produced using standard winemaking practices and then sterile filtered prior to MLF. Wines were inoculated for MLF using three different commercial O. oeni strains—Vinoflora Oenos (VFO), Enoferm Alpha and VP41—while a portion of wine remained uninoculated for a control. At the completion of MLF, different color components were measured, and the wines were aged for nine months, throughout which time color was also assessed.

Wine was also produced where the alcoholic and malolactic fermentations were carried out simultaneously with the addition of O. oeni VFO at the beginning of the alcoholic fermentation. Lower red color (measured as absorbance at 520 nanometers, or nm) was noted in wines that had undergone MLF compared to the control wine, which did not undergo MLF (see graphs on page 59).

The reduced color persisted throughout aging, as after 270 days there was up to 20% lower red color measured in wines that had undergone MLF compared to the control. Wines that were produced by simultaneous MLF demonstrated the same decrease in color as wines that were inoculated for MLF post-alcoholic fermentation.

The lower color in the MLF wines corresponded with decreased polymeric pigment and higher concentrations of the more unstable monomeric anthocyanins. Analysis of the wines also revealed that the majority of acetaldehyde and pyruvic acid was degraded by O. oeni during MLF. Because of the potential role that acetaldehyde and pyruvic acid can play in the formation of color compounds, an additional study was performed to understand the significance of their removal by O. oeni on red wine color development.5

Pinot Noir wines were inoculated for MLF with O. oeni VFO. At the completion of MLF, acetaldehyde and pyruvic acid concentrations were measured in these wines as well as a control wine that did not undergo MLF. Acetaldehyde or pyruvic acid was then added back to the MLF wines so as to equal the concentration measured in the control wine.

Color was assessed at zero and 90 days aging. While addition of pyruvic acid did not significantly impact color, addition of acetaldehyde reduced the amount of color difference between the control wine and MLF wines (see graphs on page 60). This was also reflected in the amount of polymeric pigment and monomeric anthocyanins in these wines.

Wines where acetaldehyde had been added back had significantly higher polymeric content than MLF wines that had no addition. For example: After 90 days of aging, MLF wine with no addition had approximately 41% less polymeric pigment than the control wine, while the acetaldehyde addition treatment only had an 18% reduction.

Delaying MLF to improve color One strategy that winemakers adopt to improve Pinot Noir color is to delay MLF. Anecdotally, winemakers have reported that long or delayed MLF tends to produce wines with greater color. This observation was investigated by delaying MLF for up to six months.5 Although delaying MLF did not have a significant impact on color loss at 520 nm (see graphs above), it did impact the formation of polymeric pigments.

As MLF was delayed for longer periods of time, the polymeric pigment content and monomeric anthocyanin concentration of wines that underwent MLF became more similar to those of the control. In fact, when MLF was delayed for 200 days, the polymeric pigment content and monomeric anthocyanin concentrations were the same as the control wine that did not undergo MLF. From a practical winemaking point of view, delaying the MLF for 200 days to improve color does carry some risk.

No SO2 additions can be made until MLF has been completed. Wine would therefore be at risk for microbial spoilage during this time, and so it would need to be stored cool (under 55o F) to minimize the risk of microbial growth. The risk of delaying the addition of SO2 versus improving wine color would have to be carefully considered by the winemaker on a case-by-case basis.

The improved polymeric pigment formation in wines where MLF was delayed was likely due to acetaldehyde being present in the wine for an extended period of time. A number of studies have reported the ability of O. oeni to degrade acetaldehyde in wine,16,19 and acetaldehyde is known to play a role in the formation of polymeric pigments. This is also supported by improved color and polymeric pigment content when acetaldehyde was added back to the wine post-MLF.

While metabolism of acetaldehyde by O. oeni explained some color loss, it did not explain all of it. Therefore, an experiment was conducted to investigate the adsorption of anthocyanins to O. oeni cell walls (as has been shown to occur with yeast cell walls),12,15 to determine whether this could account for the remainder of the observed color loss.

Addition of inactivated O. oeni cells at a high cell population that would be found at the end of MLF did not, however, cause a loss in color at 520 nm or monomeric anthocyanin concentration. This is in contrast to what has been reported for wine yeast but may be due to the smaller relative surface area of the bacteria or due to the likely different electrostatic nature of a bacterial cell wall compared to a yeast cell wall.

Conclusions Anecdotally, winemakers have reported that MLF can cause a loss of color in red wines, but the cause of this has not been known. In the present study it was demonstrated that MLF can cause a significant loss of color independent of the pH change that always accompanies this metabolic process. The color loss corresponded with lower polymeric pigments in wine that underwent MLF and may be related to the degradation of acetaldehyde by O. oeni. Lower color and polymeric pigment content was observed regardless of whether MLF occurred simultaneously or after alcoholic fermentation, and no differences between O. oeni strains were noted.

Results from this study suggest that winemakers may be able to improve the polymeric pigment content of Pinot Noir by delaying MLF. The wine would, however, be at risk for microbial spoilage during this time and should be stored at a cool temperature (under 55° F) to minimize the risk of microbial growth.21

Research will continue into additional techniques that may add to the formation of polymeric pigment prior to MLF. As only three O. oeni strains were utilized in the present study, additional malolactic bacteria strains will be tested to determine if strain selection can aid in the retention of color and polymeric pigments during the MLF process.

James Osborne is an associate professor and enology extension specialist in the Department of Food Science and Technology at Oregon State University. His research focuses on the impact of wine microorganisms such as wine lactic acid bacteria and Brettanomyces on wine quality. Osborne also teaches undergraduate and graduate classes in wine production and analysis. This work was made possible by grants from the Oregon Wine Board and the American Vineyard Foundation. The authors would like to acknowledge support from the Oregon Wine Research Institute and OSU.