By: Denise M. Gardner
In previous blog posts, we covered an introduction to what anthocyanins (red wine color pigments) are and how they can be stabilized in wine. Additionally, Marlena Sheridan recently discussed current research on acetaldehyde-bridging amongst anthocyanins or anthocyanin and tannin substances in wine.
This post will evaluate several techniques used during red winemaking, and what the scientific literature has found regarding their impact on red wine color stability.
Anthocyanins undergo three main phases during the course of a wine’s life:
- Development in the grape
- Extraction during primary fermentation
- Stabilization through the life of the wine
While vineyard development is an important aspect of color stabilization, as starting anthocyanin concentration will ultimately determine potential processing decisions for winemakers, the following processes are reflective of winemaking techniques believed to affect red wine color stabilization. As you siphon through the various techniques, please remember that there is no one fix-all solution to improve red wine color stability. Wine is a complex matrix, and results may vary from one variety to the next, or from one vintage to the next.
Cold soak is a pre-fermentation process in which grape must is held at low (≤10°C, ≤50°F) temperatures. There are various ways to execute a cold soak step in wine production:
- Placing a holding vessel (i.e., a macrobin) in a cool, ambient environment
- Use of tank temperature control
- Use of dry ice
Cold soaking grape must is believed to increase anthocyanin extraction pre-fermentation. Increasing anthocyanin extraction would make stabilization reactions more favorable, pushing equilibrium to building stable anthocyanin-complexes through and after fermentation.
However, several studies have investigated the use of cold soak on various red wine varieties. In two Pinot Noir studies (Gerbaux 1993, Feuillat 1996, Sacchi et al. 2005*), detrimental effects to color were found on Burgundian wines when cold soak was used pre-fermentation. Similarly, Heatherbell et al. (1996) found no difference in wine color for those wines that were cold soaked versus the non-cold soaked controls.
A study that tested freezing must, however, had a different impact on the finished wine color. The variety evaluated was Merlot, and musts were frozen with dry ice. An increase in anthocyanin concentration by 50% and increase in overall tannin concentration by 52% was found in finished wines in which grape must had been frozen pre-fermentation, compared to an untreated grape must, control wines (Couasnon 1999, Sacchi et al. 2005*). Freezing may have a greater effect on anthocyanin concentration, as freezing physically causes berry cells to burst and release its contents.
Practical Winemaking Application: Winemakers do not need to utilize a cold soaking step to increase anthocyanin extraction or improve red wine color stability, as most research suggests there is no effect regarding red wine color stability. However, it is important to note that little research has been conducted regarding potential extraction of phenol and/or tannin complexes (including polymeric pigment content) during the cold soak step.
Saignée is the French term for “bleed,” and is utilized as a winemaking technique for making rosé wines by “bleeding off” free-run juice from macerated red grapes. While the free-run juice may be used for rosé production, many winemakers utilize the saignée technique to concentrate (increase extraction) of anthocyanins and tannins in the juice that will be made into a finished red wine. Secondary effects may also increase flavor concentration.
In 1972, Singleton found that the use of saignée increased the flavonoid and anothocyanin concentrations in the concentrated red wine, four months post-fermentation. Gerbaux (1993) found slight increases in color (through sensory analysis) and phenolics of young Pinot Noir wines that had been subjected to saignée practices. However, unlike Singleton, Gerbaux’s study did not find increases in anthocyanin concentration. However, Gawel et al. (2001) found initial increases in anthocyanin concentrations at the end of primary fermentation in pressed Syrah wines, but these concentrations were depleted after 6-months post-fermentation. This study did not investigate the fate of monomeric anthocyanins, and depleted concentrations of anthocyanins were likely caused by potential polymerization or adsorption of anthocynanins onto various other wine constituents (e.g. dead yeast cells, tartrates).
Practical Winemaking Application: While the causes of potential increased color stability are unclear, the use of saignée to concentrate red grape must appears to have a positive outcome on the wine’s color stability properties. Currently, there is no evidence that removal of 10% free-run juice is less beneficial than removal of 20%. However, as saignée is a concentration method, if the grapes are of low quality, the winemaker will only concentrate other poor quality components (i.e. off-flavors, excessive tannin, etc.) with use of this technique.
Micro-ox is the “addition of dissolved oxygen at controlled dosage rates at or less than the oxygen uptake rate of wine” (Paul 2002). According to Dykes (2007), typical dosages rates range from 2 – 90 mg of oxygen per liter of wine per month. The utilization of micro-ox is believed to affect the stabilization of red wine color pigments, and therefore requires adequate starting material (i.e. anthocyanins, phenolics/tannins) in order for this method to be effective.
Theoretically, when used between primary fermentation and malolactic fermentation, the integration of dissolved oxygen should provide the chemical constituents needed to initiate polymeric pigment formation of monomeric anthocyanins. Micro-ox is used as a driving force to influence acetaldehyde concentration and influence acetaldehyde-bridged complexes previously described by Marlena Sheridan. One previous study has shown no rise in acetaldehyde contraction by use of micro-ox (Pozo et al. 2010). However, this study did find that wines subjected to micro-ox treatment did have an increased concentration of sulfite-resistant pigments. Many other wine experts have written on the use of micro-ox, and there is a world of scientific literature available regarding its use and outcomes in red wines, with varied guaranteed consensus. Additionally, micro-ox has potential to alter other characteristics of wines, including mouthfeel or flavor, in both positive and negative ways, which is often dependent on the starting wine chemistry. The extent of this summary does not nearly cover the depth of research regarding micro-ox in wine production, and will be tabled for a later date.
Practical Winemaking Application: The use of micro-oxygenation may be a powerful tool to enhance anothocyanin stabilization. Winemakers are encouraged to work with the unit’s supplier or a consultant with micro-oxygenation experience prior to implementing this strategy into processing procedures. Anecdotally, at Penn State, we have noticed little success of micro-oxygenation to improve red wine color when used on wines that have relatively low anothocyanin concentrations (<200 mg/L GAE).
Thermovinification is a technique that uses a brief heating step to grape must or juice, and subjecting it temperatures above 60°C (140°F). It is believed that thermovinification enhances both extraction and stabilization of anthocyanins.
Auw et al. (1996) found that the use of thermovinification increased the concentration of free, monomeric anthocyanins in both Cabernet Sauvignon and Chambourcin wines. Additionally, this study also found increased concentrations of phenolics in the Chambourcin wine treated with thermovinification pre-fermentation, and a lower phenolic content in Cabernet Sauvignon wines treated with thermovinification. This emphasizes that solutions to improve color stability may vary depending on the grape variety and its heritage (i.e. native variety vs. hybrid vs. V. vinifera). Additionally, Sacchi et al. (2005) also concluded that it is necessary to have some skin contact time with grape skins after thermovinification treatment in order to enhance extraction of anthocyanins.
Practical Winemaking Application: The use of thermovinification to improve red wine color stability may be a practical tool for red wines, especially those red wines with minimal aging requirement. Thermovinification is not recommended for red wines destined for long term aging. It should be noted that thermovinification may alter flavor of the finished wines. A winery should evaluate the potential sensory impact of thermovinification prior to committing all wines to this process.
Extended Maceration is the process of allowing skins and seeds in contact with the finished red wine, post-fermentation, for an extended period of time. Various studies researching the effects of extended maceration on red wines have found increased concentrations of tannins, especially tannins from grape seeds. However, this process has not been shown to increase extraction or concentration of anthocyanins.
Auw et al. (1996) found that a thermovinification treatment was more effective at increasing phenolic composition compared to extended maceration for Chambourcin wines, but that for Cabernet Sauvignon wines, extended maceration was more effective at increasing phenolic concentrations. Watson et al. (1994, 1995) also found an increase in flavanol and polymeric pigment extraction in Pinot Noir wines that underwent extended maceration.
Practical Winemaking Application: Extended maceration will not increase free monomeric anthocyanin concentrations. This practice should only be utilized for winemakers wishing to increase tannin-based extractions. For a review on why the effects of extended maceration may be focused on phenolic extraction, please see Dr. Anna Katharine Mansfield’s recently published article, “A Few Truths About Phenolics,” in Wines & Vines.
Delayed Malolactic Fermentation (MLF)
The most current scientific literature on delayed MLF is coming out of Dr. James Osborne’s lab in Oregon. This practice is literally as it sounds: winemakers allow a wine to finish primary fermentation and wait (without addition of sulfur dioxide) for a specific period of time until MLF progresses naturally or is inoculated. This is an anthocyanin stabilization processing technique.
On studies in Pinot Noir, James and Osborne (2014) found that a 200 day delay in MLF was required for wines that went through MLF to reach a similar concentration of polymeric pigment, statistically, as the control wine that did not undergo MLF. It is important to remember that in order to maintain stability of wines not treated with sulfur dioxide, adequate temperature control (i.e. maintaining the cellar at 50-55°F or 10-13°C) will cause polymeric pigment formation reactions to progress slowly, which may influence why so much time is needed in delaying MLF. While increase temperature would increase the rate of polymeric pigment formation reactions, the increase in temperature also puts wines at greater risk for microbial spoilage.
Practical Winemaking Application: The jury is not out on this practice! Although some winemakers swear this practice works, it is important to remember than many wineries do not run “control” treatments for various practices. As there is much vintage-to-vintage variation amongst wines, it is challenging to draw solid conclusions from commercial wineries that do not utilize a control treatment. Currently, the literature states a delay in MLF may effectively improve color, but the time required for that delay may not be practical from a commercial operation standpoint. Additionally, winemakers must maintain effective strategies at monitoring potential spoilage during a vulnerable period of time when the wine is not protected by preservatives (sulfur dioxide).
While this blog post covers several techniques believed to affect red wine color stability, the review article by Sacchi et al. covers several additional topics including: yeast selection, fermentation temperature, the effects of sulfur dioxide, carbonic maceration, the use of pectolytic enzymes, and utilization of pump-overs and punch downs during primary fermentation. The review of the current scientific understanding of these practices (up to research literature published through 2005) can be found in the American Journal of Enology and Viticulture (AJEV).
Sacchi et al. 2005* The following authors (Couasnon 1999, Feuillat 1996, and Gerbaux 1993) were included in the Sacchi et al. 2005 review article. As initial research article was in another language, information regarding these studies was obtained from Sachhi et al. 2005.
Auw, J.W., V. Blanco, S.F. O’Keefe, and C.A. Sims. 1996. Effect of processing on the phenolics and color of Cabernet Sauvignon, Chambourcin, and Noble wines and juices. Am. J. Enol. Vitic. 47(3):279-286.
Burns, T.R. and J.P. Osborne. 2014. Loss of Pinot Noir wine color and polymeric pigment after malolactic fermentation and potential causes. Am. J. Enol. Vitic.
Couasnon, M.B. 1999. Une nouvelle technique: La maceration préfermentaire à froid-extraction à la neige carbonique. Premiér partie: Résultats oenologiques. Rev. Oenol. 92:26-30.
Dykes, S. 2007. The effect of oxygen dosage rate on chemical and sensory changes occurring during micro-oxygenation of New Zealand red wine. Diss. Food Sci. Univ. of Auckland.
Feuillat, M. 1996. Vinification du Pinot Noir en Bourgogne par maceration préfermentaire à froid. Rev. Oenol. 83:29-31.
Gawel, R., P.G. Iland, P.A. Leske, and C.G. Dunn. 2001. Compositional and sensory differences in Syrah wines following juice run-off prior to fermentation. J. Wine Res. 12(1): 5-18.
Gerbaux, V. 1993. Etude: de quelques conditions de cuvaison susceptibles d’augmenter la composition polyphénolique des vins de Pinot Noir. Rev. Oenol. 69:15-18.
Heatherbell, D., M. Dicey, S. Goldsworthy, and L. Vanhanen. 1996. Effect of cold maceration on the composition, color, and flavor of Pinot Noir wine. In Proceedings of the Fourth International Symposium on Cool Climate Enology and Viticulture. T. Henick-Kling et al. (Eds.), pp. VI: 10-17. New York State Agricultural Experiment Station, Geneva.
Paul, R. 2002. Micro-oxygentation – Where now.” Australian Society of Viticulture and Oenology, Uses of Gases in Winemaking Seminar Proceedings.
Pozo, A.G., I. Arozarena, M.-J. Noriega, M. Navarro, and A. Casp. 2010. Short- and long-term effects of micro-oxygenation treatments on the colour and phenolic composition of a Cabernet Sauvignon wine aged in barrels and/or bottles. Eur. Food Res. Technol. 231: 589-601
Sacchi, K.L., L.F. Bisson, and D.O. Adams. 2005. A review of winemaking techniques on phenolic extraction in red wines. Am. J. Enol. Vitic. 56(3):197-206.
Singleton, V.L. 1972. Effects on red wine quality of removing juice before fermentation to simulate variation in berry size. Am. J. Enol. Vitic. 23:106-113.
Watson, B.T., S.F. Price, H.P. Chen, and M. Valladao. 1994. Pinot Noir processing effects on wine color and phenolics. Abstr. Am. J. Enol. Vitic. 45:471-472.
Watson, B.T., S.F. Price, and M. Valladao. 1995. Effect of fermentation practices on anthocyanin and phenolic composition of Pinot Noir wines. Abstr. Am. J. Enol. Vitic. 46:404.