Sulfur Dioxide Management during Aging is an Important Factor for the Development of Rosé Wine Color

Transcription

1 ASEV CATALYST REPORT Sulfur Dioxide Management during Aging is an Important Factor for the Development of Rosé Wine Color Caroline P. Merrell 1 and James F. Harbertson 1,2 * 1 Washington State University, 2710 University Drive, Richland, WA ; and 2 Associate Professor of Enology, Washington State University, Viticulture and Enology Program, School of Food Science. *Corresponding author (jfharbertson@wsu.edu) Acknowledgments: Ste. Michelle Wine Estates are thanked for fruit donation. Richard Larsen and Colin Hickey are thanked for winemaking assistance, and Maria Mireles is thanked for harvest laboratory analysis. The Wine Research Advisory Committee, the Washington Wine Commission, the Washington Grape and Wine Research Program, and the WSU Agricultural Research Center are thanked for their generous funding of this research. Manuscript submitted Feb 14, 2017, revised Aug 10, 2017, accepted Aug 18, 2017 Copyright 2017 by the American Society for Enology and Viticulture. All rights reserved. Summary Goals: The goal of this project was to determine the impact of sulfur dioxide (SO2) and berry maturity on the color of Syrah rosé wines through fermentation and accelerated aging. This project also set out to determine the best methodology for measuring potential color of rosé wines, by measuring anthocyanin bound to SO Key Findings: Acetaldehyde was found to be the most suitable reagent for reacting with SO2 bound to anthocyanin and releasing potential color of rosé wines. Color in rosé wines was impacted by fruit maturity and decreased during fermentation. SO2 treatment had no impact on rosé color by the end of fermentation. 1 Copyright 2017 by.

2 During aging, absorbance at 520nm increased over time, and was impacted by fruit maturity and SO2 treatment. Final absorbance at 520nm after 8 weeks accelerated aging was accurately predicted by a reaction with acetaldehyde prior to aging. When analyzed with tri-stimulus color measurements, fruit maturity and SO2 content impacted visual intensity of red and yellow hue over time. Impact and Significance: This study gives winemakers tools to measure apparent and potential color in rosé wines. In both 22 and 24 Brix fruit, wines retained only 27-38% of the initial color by the end of fermentation. The level of SO2 added to wine had no impact on post fermentation color, but levels of SO2 added prior to aging did impact long-term color. The potential for a rosé wine to darken over time was influenced by how much color the wine initially had, and SO2 concentrations had a larger impact on color development in wines with more color initially. 40 Key words: color, color stability, polymeric pigment, rosé wine, sulfur dioxide, wine aging Overview The color of rosé wines is a major quality indicator and largely impacts consumer preference. Anthocyanins, which are extracted from grape skins during maceration, are responsible for color in wine grapes and therefore, rosé wines. 1 Once anthocyanins are extracted into solution, they are relatively unstable and react with sulfite and water to form colorless compounds. 2 Over time anthocyanins react to form more stable color compounds, called polymeric pigments, which are resistant to bleaching by sulfite. In red wine, polymeric pigments are primarily the result of reactions between anthocyanins and tannins. 3-5 However, in rosé wine there is limited extraction of tannins due to limited skin and seed contact. Therefore, polymeric pigments in rosé wine are primarily low molecular weight compounds, which are formed by reactions 2

3 between anthocyanins and yeast metabolites. 6-8 While these compounds are not all polymers, this nomenclature is commonly used to describe the diverse group of pigments. Additionally, copigmentation is a phenomenon that occurs in red wines when anthocyanins interact with other molecules, called co-factors, and results in an overall color that is greater than the concentration of anthocyanin alone accounts for. 9 However, the concentration of anthocyanins must be greater than 18.5 mg/l, which is not normally reached in rosé wines. 9 There are multiple ways to produce a rosé wine, from simply a short maceration time, to saignée of red juice, to blending red and white wines together. Regardless of the way the rosé wine is produced, anthocyanins are extracted from the grape skins. With anthocyanin present in the wine, polymeric pigments can form over time. 4 The formation of polymeric pigments over time, as well as the loss of SO2 and the release of bleached monomeric anthocyanins contributes to the darkening color of rosé wine over time. Studies have examined various winemaking treatments on rosé wine color such as maceration time, temperature, and the addition of enzymes However, there is limited work on the effect of SO2 during fermentation and aging. Additionally, many of the previous studies have not tracked color during both fermentation and wine aging. Since color is a major quality indicator, this study set out to determine the extent of color change with different levels of initial color (resulting from different fruit maturities) and SO2 levels. Additionally, research on rosé wine color measurements has been focused on developing CIE or tristimulus values, 13 or HPLC techniques. 11 However, due to cost many wineries do not have access to these techniques. This work also sets out to determine a simple absorbance method for measuring rosé wine color, which could be easily implemented in wineries. 3

4 Major Observations and Interpretations Color Measurement Nomenclature Throughout this study, color was measured by the absorbance at 520 nm, due to the simplicity of the measurement and the ability to implement these readings into a practical winery setting. Other methodology to measure anthocyanin content also relies on absorbance at 520 nm, since the pigments absorbance at this wavelength. 14 Polymeric pigments were measured by reading absorbance at 520 nm after bleaching monomeric anthocyanin with SO2. Potential color was measured by reacting acetaldehyde with wine to release any anthocyanin that was bound to and temporarily bleached by SO2. Finally, CIELAB data was collected in order to gather more descriptive information on color changes Fermentation Results Syrah fruit was harvested at approximately 22 and 24 Brix (Table 1). Fruit did not have significantly different levels of anthocyanin, but post press juice did differ significantly (Figure 1). For all the wines, color dropped dramatically throughout fermentation. In both 22 and 24 Brix fruit, low and high SO2 treatments had the same color by the end of fermentation. In the wine made from the 22 Brix fruit, the high SO2 treatment had significantly less color throughout fermentation. However, by day 8 of fermentation, the color was the same as the low SO2 treatment. For the wine made from the 24 Brix fruit, the low and high SO2 treatments had the same color by day 4 of fermentation. Polymeric pigment (pigment that was resistant to bleaching by SO2) and potential color measurements also dropped throughout fermentation (data not 4

5 94 95 shown). The amount of color retained from press to end of fermentation was only approximately 38% for 22 Brix fruit and approximately 27% for the 24 Brix fruit Development of Potential Color Measurements After fermentation, the color of rosé wines cannot always be measured directly by absorbance at 520 nm, due to some anthocyanins being bound and bleached by SO2. Therefore, total potential color can be obtained by adding a strong electrophile, like hydrogen peroxide or acetaldehyde to free the bound SO2. Due to the cost and availability of hydrogen peroxide as compared to acetaldehyde it is an attractive option. However, hydrogen peroxide released bound anthocyanin only briefly, before continuing to oxidize and degrade the anthocyanin. This is evidenced by a decline in absorbance after a peak was reached (Figure 2). Additionally, when higher quantities of hydrogen peroxide were added to wine, this degradation occurred even faster. In contrast, the reaction with acetaldehyde reached a maximum after approximately 45 minutes, and absorbance did not decline. The absorbance was also measured 24 hours after addition and only decreased approximately 5%, suggesting that the reaction could be left overnight. Finally, the maximum absorbance after hydrogen peroxide was added was less than what was reached with acetaldehyde. Therefore, hydrogen peroxide was not a suitable reagent for determining potential (bound) color, but acetaldehyde could be utilized

6 Aging Results In both wines, absorbance at 520 nm (Figure 3) and polymeric pigment content (Figure 4) increased over time. For the wine made from 22 Brix fruit, absorbance at 520nm increased slightly, but then leveled off over time. At week 8 of incubation, all treatments (Brix and SO2 level) were significantly different for absorbance at 520nm and polymeric pigment content. Wine made from 24 Brix fruit had a higher absorbance than wine made from 22 Brix fruit, and the low SO2 treatments were always higher in absorbance than the high SO2 treatments. For both 22 and 24 Brix wines, the potential color (A520nm) measured prior to incubator aging (week 0) of was approximately equal to the final color after 8 weeks in the incubator (Figure 5). While there are statistical differences between some of the potential and final color readings, there was not a large practical or visual difference. The statistical significance is due to the small standard error (maximum of 1.5%). However, the largest variation between predicted color and final color was only 9%. For wines made from 24 Brix fruit, time and SO2 treatment were statistically significant for red and yellow hue of wines. Red hue decreased slightly over time for wine made from 22 Brix fruit, and differences between SO2 treatments were negligible (Figure 6). For wine made from the 24 Brix fruit, redness increased over time and reached a steady value. After 8 weeks aging, the low SO2 treatment had a significantly higher intensity of red hue. Yellow hue also increased as wine aged for both maturities, and similarly to red hue, the effects were much greater for wines made from 24 Brix fruit (Figure 7). At week 8, the wines made from 22 Brix fruit were at similar levels of yellow hue, while in the wine made from 24 Brix fruit, the low SO2 treatment was more yellow than the high SO2 treatment. Wine made from 22 Brix fruit was 6

7 significantly lower in red and yellow hue intensity than wine made from 24 Brix fruit. As discussed previously, polymeric pigment formation, which most likely corresponds to this yellowing, also increased over time and treatment trends were similar for polymeric pigment formation (Figure 4) and yellow hue increase (Figure 7). The lightness attribute decreased slightly over time, but no major changes were observed (data not shown). This indicates that the changes to red and yellow hue correspond to the perceived darkening over time rather than an actual decrease in lightness. Figure 8 illustrates the color changes over time from CIELAB data. Color changes to the wine made from 22 Brix fruit were minimal, however, the wine made from the 24 Brix fruit became more intensely colored over time. Broader Impact Pinking is a phenomenon that is characterized by the development of a pink color in wines made from white grape cultivars. This phenomena occurs in wine made from white grapes that have a small amount of anthocyanin pigment in the skins, such as Pinot Gris or Gewürztraminer. In white wine, it has been observed that pinking occurs over time when SO2 levels decrease, therefore releasing bound anthocyanin that was present in the wine. 15 Over time, this free anthocyanin reacts to form polymeric pigments that are then resistant to bleaching by SO2. This evolution of white wine pinking is extremely similar to the chemical evolution of rosé wine color, which leads to the darkening of color over time. In order to measure potential pinking in white wines, the use of hydrogen peroxide has been suggested. 15, 16 However, hydrogen peroxide cannot adequately predict the total color of wines due to the oxidative degradation of anthocyanins. For both potential pinking due to the presence of anthocyanins, as 7

8 well as potential color of rosé wines, acetaldehyde is potentially a better option due to the persistence of the color. Since the majority of color (including bound anthocyanin) was lost during fermentation, measuring potential color during active fermentation was not beneficial. A decline in anthocyanin concentration in the absence of grape skins has been observed previously and can be partially attributed to interactions with yeast. 17 Additionally, fermentation in the absence of skins and seeds leads to wines without significant extraction of tannins. Reactions between anthocyanin and tannin have been observed to increase stability of the pigments. 18 Therefore, this loss of anthocyanin during fermentation is due to both adsorption on lees and the instability of the pigment. While not beneficial during fermentation, potential color measured immediately prior to aging (after SO2 addition) was a good predictor of final wine color (Figure 5). While tri-stimulus color measurements continue to be the most descriptive tool for measuring rosé wine color and change, absorbance at 520 nm can also be utilized to track and estimate final color. Absorbance values are also more realistic for wineries to measure than CIELAB or HPLC, making this methodology practical for predicting and measuring color changes. The use of SO2 is a valuable tool to control color in rosé wines. Levels of SO2 prior to fermentation did not impact post-fermentation color. However, the level of SO2 added before aging had a significant impact on the absorbance and hue of the wine. Additionally, polymeric pigment content was dependent on both fruit maturity and SO2 treatment. Wines higher in SO2 had a lower formation of polymeric pigment. With increasing levels of SO2, there is an increased number of anthocyanins weakly bound with SO2. Our results suggest that anthocyanins 8

9 that are bound to SO2 don t appear to react with other compounds to form polymeric pigments. Additionally, wines that began with more color post-fermentation had more polymeric pigment formation, due to an increased amount of anthocyanin. In wines made from 24 Brix fruit, the increase in red hue for the low SO2 treatment corresponds to more monomeric (and not sulfite bleached) anthocyanin and the increase in yellow hue corresponds to higher polymeric pigment content. Due to this impact on polymeric pigment formation, hue and absorbance at 520 nm, SO2 management before bottling is the most critical time point for managing long-term rosé wine color. The wine made from 24 Brix fruit had slightly different aging patterns than the wine made from 22 Brix fruit. This indicates that when wines have more color initially, they have more potential to change color in the bottle. Wine made from 24 Brix fruit had significantly higher absorbance after fermentation, and a higher potential color at week 0 of incubator aging, indicating the wines had more color than wines made from 22 Brix fruit. The wine made from the 22 Brix fruit did not increase color in the bottle drastically, and SO2 level had less of an impact on color changes. However, the wine made from the 24 Brix fruit had large color changes in the bottle and SO2 treatment had a major impact on color. Special attention should be paid to SO2 decisions to limit color darkening in the bottle when fruit is riper or has more initial color. Incubator aging has been utilized in previous studies to accelerate the effects of aging. 3,19 In red wine, it has been observed that approximately one month in the incubator corresponds to one year in the cellar. 19 While red and rosé wines age slightly differently due to differences in phenolic content, the 8-week time point roughly correlates to 2 years in the cellar. Additionally, 9

10 plastic tubes used in the study for aging allow slightly more oxygen into the samples than glass wine bottles. Tubes were flushed with argon prior to aging to minimize these effects. However, this increase in oxygen content may oxidize anthocyanins, lowering absorbance at 520 nm in incubated samples as compared to cellar-aged samples. From a practical winemaking point of view, winemakers can set final color absorbance goals and adjust winemaking decisions accordingly. In this study, picking decisions were varied in order to manipulate starting wine color. However, pressure reached during the press cycle or time on skins can also change extraction levels. Since wines are expected to retain only between 27-38% of post press color, final absorbance values can be estimated from initial, post-press color. Riper fruit can be desirable for rosé wine production due to the increase in ripe aromas and flavors. However, wine made from less ripe fruit, which finished fermentation at an absorbance value below 0.1 did not drastically change color during aging, while wine with more initial color, which finished fermentation at an absorbance of 0.2, did darken substantially in the bottle. If riper fruit is desired, the potential color reading could be utilized before bottling to predict final color based on anthocyanin release from SO2 over time, and SO2 could be adjusted accordingly. While lowering initial wine color through fruit maturity was the most effective way to limit darkening over time, the use of SO2 can also help winemaker s control color increase during aging

11 223 Experimental Design Winemaking The experiment was conducted during the 2016-growing season in the Columbia Valley AVA of Washington State. Syrah was manually harvested at 22 and 24 Brix (day of year 242, 265) in order to have fruit with different levels of initial color. Fruit went direct to press (bladder press; Zambelli Enotech, Camisano Vicentino, Italy) with a final pressure of 2 bar. Winemaking was conducted in triplicate on a 20 L scale at the Washington State University Wine Science Center. Potassium metabisulfite was added directly after juice was pressed to reach a final SO2 concentration of 25 and 50 ppm (low and high treatments, respectively). KS enzyme was added prior to inoculation at ml/l juice (Scott Laboratories, Petaluma, CA). Juice was inoculated with Lalvin EC 1118 at 10 6 cells/ml (Lallemand, Montreal, Canada). Fermaid K (0.25 g/l) and GoFerm (0.3 g/l in yeast rehydration) were added to the each carboy immediately after inoculation (Scott Laboratories, Petaluma, CA). Fermentations were sampled every other day and fermentations were monitored with a portable density meter (Anton Paar, Ashland, VA). When fermentation had finished, wines were cold stabilized at 0 o C. After cold stabilization, samples were collected and potassium metabisulfite was added to reach 0.4 and 0.8 mg/l free molecular SO2 (low and high SO2 treatments, respectively). SO2 levels were measured enzymatically (Admeo, Hollister, CA) and further additions were made until the concentration of free SO2 was stable. Four 50 ml samples from each fermentation replicate were then placed in centrifuge tubes, topped with argon gas, and placed in a 30 o C incubator (VWR, Radnor, PA) in order to simulate aging. One set of 11

12 sample tubes was analyzed every 2 weeks for 8 weeks, giving triplicate aging samples for each maturity and SO2 treatment Color Measurements Acetaldehyde has long been used in excess to react with SO2, and free bound anthocyanin pigment. 20, 21 Hydrogen peroxide has similar chemical properties to acetaldehyde, 15, 16 and is an inexpensive option. In order to test the suitability of both acetaldehyde and hydrogen peroxide for this reaction, different concentrations were added to wine samples, and absorbance readings were taken every 5 minutes. During fermentation and aging, absorbance was measured at 520 nm (Agilent, Santa Clara, CA). Potassium metabisulfite was added to wine samples (80 μl in 1 ml wine; 10 minute incubation) to measure total polymeric pigment. 22 Acetaldehyde was added to samples (10 μl of 10% acetaldehyde solution in 1 ml wine; 45 minute incubation) to measure total potential color. 20, 21 During incubator aging, samples were also measured for tri-stimulus color values using a CR-400 Chroma Meter (Konica Minolta, Ramsey, NJ). Fermentation samples were not measured with tri-stimulus color due to limited sample volume Statistical Analysis Statistical analysis was performed with one- and two-way analysis of variance using Minitab 17 (State College, PA). Separation of the means was accomplished using Fisher s LSD with a significance value established as p<

13 References and Footnotes 1. Mazza G, and Francis FJ Anthocyanins in grapes and grape products. Crit Rev Food Sci Nutr 35: Fulcrand H, Dueñas M, Salas E, and Cheynier V Phenolic reactions during winemaking and aging. Am J Enol Vitic 57: Salas E, Fulcrand H, Meudec E, and Chéynier V Reactions of anthocyanins and tannins in model solutions. J Agric Food Chem 51: Somers TC The polymeric nature of wine pigments. Phytochemistry 10: Remy S, Fulcrand H, Labarbe B, Cheynier V, and Moutounet M First confirmation in red wine of products resulting from direct anthocyanin-tannin reactions. J Sci Food Agric 80: Fulcrand H, Cameira dos Santos P, Sarni-Manchado P, Chenyier V, and Favre-Bonvin J Structure of new anthocyanin-derived wine pigments. J Chem Soc, Perkin Trans. 1 1: Fulcrand H, Benabdeljalil C, Rigaud J, Cheynier V, and Moutounet M A new class of wine pigments generated by reaction between pyruvic acid and grape anthocyanins. Phytochemistry 47: Bakker J, and Timberlake CF Isolation, identification, and characterization of new color-stable anthocyanins occurring in some red wines. J Agric Food Chem 45: Boulton R The copigmentation of anthocyanins and its role in the color of red wine: a critical review. Am J Enol Vit 52: Pue rtolas E, Saldan a G, A lvarez I, and Raso J Experimental design approach for the evaluation of anthocyanin content of rose wines obtained by pulsed electric fields. Influence of temperature and time of maceration. Food Chem 126: Kelebek H, Canbas A, and Selli S HPLC-DAD-MS Analysis of anthocyanins in rosé wine made from cv. Öküzgözü grapes, and effect of maceration time on anthocyanin content. Chromatographia 66: Salinas MR, Garijo J, Pardo F, Zalacain A, and Alonso GL Color, polyphenol, and aroma compounds in rose wines after prefermentative maceration and enzymatic treatments. Am J Enol Vit 54: Ayala F, Echávarri JF, and Negueruela AI A new simplified method for measuring the color of wines. I. Red and rosé wines. Am J Enol Vit 48: Harbertson JF, and Spayd S Measuring phenolics in the winery. Am J Enol Vitic 57: Andrea-Silva J, Cosme F, Ribeiro LF, Moreira ASP, Malheiro AC, Coimbra MA, Domingues MRM, and Nunes FM Origin of the pinking phenomenon of white wines. J Agric Food Chem 62: Simpson RF Oxidative pinking in white wines. Vitis 16: Medina K, Boido E, Dellacassa E, and Carrau F Yeast interactions with anthocyanins during red wine fermentation. Am J Enol Vitic 56:

14 Singleton VL, and Trousdale EK Anthocyanin-tannin interactions explaining differences in polymeric phenols between white and red wines. Am J Enol Vitic 43: Merrell CP Phenolic evolution in wine: determination of new methodology to measure phenolic content and the impact of maturity, alcohol, and sulfur dioxide on wine color during aging. Thesis, Washington State University, Richland. 20. Somers TC, and Evans ME Spectral evaluation of young red wines: anthocyanin equilibria, total phenolics, free and molecular SO2, "chemical age". J Sci Food Agric 28: Levengood J, and Boulton R The variation in the color due to copigmentation in young Cabernet Sauvignon wines. In Red Wine Color. pp American Chemical Society. 22. Harbertson JF, Picciotto EA, and Adams DO Measurement of polymeric pigments in grape berry extracts and wine using a protein precipitation assay combined with bisulfite bleaching. Am J Enol Vit 54:

15 Table 1 Fruit chemistry from each harvest date show an increase in fruit sugar over the 2 pick dates, but no other significant changes. Values in a column not sharing a letter are significantly different at p < 0.05 (Fisher LSD). Harvest Brix ph TA Avg berry wt (g) Anthocyanin (mg/g fresh wt) DOY ± 0.2 b 3.68 ± ± ± ± 0.18 DOY ± 0.4 a 3.72 ± ± ± ± 0.14 Figure 1 Fermentation graphs of 22 Brix fruit (A) and 24 Brix fruit (B) indicate that color drops dramatically during fermentation. Means presented with standard error (n = 3). 15

16 Figure 2 Reaction kinetics for releasing bound pigment with acetaldehyde and hydrogen peroxide (H2O2) at different concentrations shows that hydrogen peroxide degrades the anthocyanin pigment. Means presented with standard error (n = 3). Figure 3 Absorbance values over incubator aging indicate a general increase in color for wine made from 24 Brix fruit but a leveling off for wine made from 22 Brix fruit. Means presented with standard error (n = 3). At week 8, data points sharing a star are not significantly different at p < 0.05 (Fisher LSD). 16

17 Figure 4 Formation of polymeric pigments (pigments resistant to bleaching by SO2) increased over time for all treatments. Means presented with standard error (n = 3). At week 8, data points sharing a star are not significantly different at p < 0.05 (Fisher LSD). Figure 5 For each maturity and SO2 treatment, potential color (measured immediately before aging) corresponds to final color after 8 weeks of incubator aging. Means presented with standard error (n = 3). Bars sharing a star are not significantly different at p < 0.05 (Fisher LSD). 17

18 Figure 6 Tri-stimulus color measurements for red hue show an increase in red hue over time for wine made from 24 Brix fruit but not 22 Brix fruit. Means presented with standard error (n = 3). At week 8, data points sharing a star are not significantly different at p < 0.05 (Fisher LSD). Figure 7 Tri-stimulus color measurements for yellow hue show an increase in yellow hue over time. Means presented with standard error (n = 3). At week 8, data points sharing a star are not significantly different at p < 0.05 (Fisher LSD). 18

19 Figure 8 CIELAB color representations of rosé wines after incubator aging. 19