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February 2016 WINES&VINES 59 PRACTICAL WINERY & VINEYARD WINEMAKING W ine 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 col- ored 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 However, the color of a red wine is not solely determined by the concentration of anthocy- canins. Following extraction, anthocyanins can react with a number of other compounds pres- ent in wine to form more complex color com- pounds. For example, anthocyanins can react with tannins to form polymeric pigments. The formation of polymeric pigments can be ac- celerated 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 (SO 2 ) than individual antho- cyanins and tend to increase as a wine ma- tures, accounting for the majority of color in older wines. 18 Impact of microorganisms on red wine color A number of viticultural and winemaking prac- tices have been demonstrated to impact the formation of polymeric pigments such as in- creased fermentation temperature, 17 extended maceration 20 and saignée. 10 In addition, a num- ber of studies have reported that yeast can impact color through the adsorption of antho- cyanins to their cell walls 12,15 or through produc- tion 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 impor- tant 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 acetalde- hyde do not remain stable during a wine's life. In particular, Oenococcus oeni is known to de- grade acetaldehyde and pyruvic acid during malolactic fermentation (MLF). 16,19 MLF and red wine color Anecdotally, winemakers have reported a de- crease 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 Shiraz 1 and Cabernet Sauvignon 6 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 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 re- Loss of Pinot Noir Color and Polymeric Pigment Measuring the effects of malolactic fermentation and possible mechanisms By James Osborne and Tresider Burns MLF AND PINOT NOIR WINE COLOR Storage time (days) Day 0 Day 270 Absorbance @ 520 nm 4.0 3.5 3.0 2.5 2.0 1.5 1.0 .5 0 n = Control n = SIM n = VP41 n = VFO n = Alpha Day 0 Day 270 Storage time (days) Absorbance @ 520 nm 1.6 1.4 1.2 1.0 .8 .6 .4 .2 0 Day 0 Day 270 Storage time (days) Anthocyanins (mg/L M-3-G eq.) 140 120 100 80 60 40 20 0 Color at 520nm (top), polymeric pigment (middle), and monomeric anthocyanins concentration (bot- tom). SIM=simultaneous alcoholic and malolactic fermentation.