October 2018 Issue of Wines & Vines
 
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Improving Red Wine Color and Mouthfeel Over Time

Maximizing polymeric pigments can help winemakers improve red-wine quality

 
by Caroline Merrell and Melissa Hansen
 
 

Formation of polymeric pigments is important for successful cellaring of red wine as they help soften wine’s astringency and provide long-lasting color. Research supported by the Washington State Wine Commission has identified factors that can maximize polymeric-pigment formation to help improve red-wine quality.

During fermentation and while red wine ages, polymeric pigments form from the reaction of anthocyanins and tannins, phenolic compounds that come mainly from the skin and seeds of the fruit. Anthocyanins contribute to the red color of grapes and wine; tannins are astringent but add flavor complexity and structure to a wine.

A study by Washington State University scientists examined the effects of fruit maturity, alcohol and wine aging on the concentration of anthocyanins, tannins and polymeric pigments in Cabernet Sauvignon and Syrah. The goal was to determine the most important factors involved in forming polymeric pigments and provide winemakers with practical guidelines to keep polymeric pigments stable in a wine environment over time.

This article summarizes the research that answers the following questions: 1) What drives polymeric pigment formation—the concentration of anthocyanins or tannins? 2) Is there a critical anthocyanin-to-tannin ratio in the fruit or wine that winemakers should target to maximize the formation of polymeric pigments?

Constant vineyard conditions
Syrah and Cabernet Sauvignon grapes were used to obtain different anthocyanin and tannin concentrations and ratios between the two compounds. Cabernet Sauvignon generally produces grapes with darker color and high levels of tannins. Syrah grapes are typically dark but lower in tannins than Cabernet Sauvignon. The two cultivars are prevalent in Washington State.

The trial was conducted in a commercial vineyard in the Columbia Valley AVA during the 2015 growing season. Fruit (1.5 tons) was harvested at three different maturity levels: 20o, 24o and 28o Brix. Harvest dates were separated by approximately three weeks between each pick.

Initial fruit-soluble solids concentration (Brix) was manipulated in the winery by removing juice (saignée) and then either sugar adjustment or water-back prior to fermentation to have three alcohol concentrations (low 11-12%, medium 14-15% and high 17%) represented at each grape maturity. (See Figure 1, Three Harvest Dates, Nine Wines.) Saignée occurred immediately after the crush to minimize anthocyanin loss while maintaining the juice-to-solids ratio across all treatments.



Picking the fruit at different maturities and making wines with different alcohol levels created variations in the wine anthocyanin and tannin concentrations and resulted in a range of anthocyanin-to-tannin (A:T) ratios from a constant set of growing conditions and vineyard location.

Effect of fruit maturity and alcohol
In the trial, ripe fruit in both Cabernet Sauvignon and Syrah had the highest anthocyanin levels among the three harvest treatments (unripe 20o Brix, ripe 24o and overripe 28o). However, wine made from overripe fruit had equal or greater anthocyanin content than wine made from ripe fruit. Wine alcohol treatments did not affect anthocyanin extraction but did increase tannin extraction. Tannin concentration was not always influenced by pick date, although the unripe Cabernet Sauvignon had significantly more tannin than wines made from the ripe and overripe fruit. Generally, riper fruit led to wine with more anthocyanins, while higher alcohol led to wine with higher tannin concentration.

Polymeric pigment content increased with both increasing fruit maturity and wine alcohol. (See Figure 2, Effect of Fruit Maturity and Alcohol on Polymeric Pigments.)

Polymeric pigment formation: no A:T ratio
Based on previous research that examined the interaction of anthocyanins and tannins, it has been suggested that the A:T ratio plays an important role in polymeric pigment formation because both tannin and anthocyanin are needed for development of polymeric pigments.6 However, past studies were conducted in isolated systems, and few have followed the polymeric pigment formation over time due to the difficulty of manipulating treatments while keeping grape growing and winemaking factors constant.

The variation of anthocyanin concentration in the trial was considerable. Anthocyanin content varied up to about two-fold in the same cultivar, and tannin concentration varied up to 1.5-fold in response to ripeness or alcohol. These variations gave a two- to three-fold difference in the A:T ratio for the same variety.

This study found the A:T ratio was a very poor predictor of polymeric pigment concentration. The best single predictor for polymeric pigment formation over time was initial wine anthocyanin content, which increased with more fruit maturity. This result contradicted the importance of A:T from previous literature.

Although initial wine anthocyanin content in this study was a strong polymeric pigment predictor, fruit anthocyanin levels did not directly correlate to wine anthocyanin content. Based on findings from this study, winemakers should focus on the initial anthocyanin concentration of wines — not fruit anthocyanin concentration — because it was the strongest predictor of polymeric pigments in Cabernet Sauvignon and Syrah wines.

Maximize polymeric pigmentation
This study found that higher fruit maturity increased anthocyanin concentrations and that higher wine alcohol increased tannin levels. Both the increased ripeness and alcohol led to the highest polymeric pigment concentrations. Therefore, the easiest way to maximize polymeric pigment formation is to use ripe, mature fruit (24°-28° Brix) and make medium- to high-alcohol (14%-17%) wine.

In regions or growing seasons where it is difficult to harvest mature, ripe fruit—but tannin levels are not a problem—the focus should be to maximize fruit and wine color. Growers can use vineyard-management practices such as keeping the canopy open, growing low-vigor vines, removing leaves in the fruit zone and implementing deficit-irrigation strategies to encourage maximum color (anthocyanin) development in the fruit.

But once grapes are picked, it is difficult for winemakers to increase color; extraction of anthocyanins in the winery is relatively quick, and concentration reaches maximum levels early in fermentation and then declines.

The trend of cold soak—holding the must at a low temperature for hours to days before fermentation—has become popular in some regions as a technique to increase color, although there is conflicting research on its effectiveness. Cold soak might extract more anthocyanin temporarily, but it does not extract additional tannins and research shows no increase in polymeric pigment formation from cold soak.1

To maximize polymeric pigment formation in low-tannin varieties such as Pinot Noir or Syrah, use vineyard and winery techniques to increase both color (see above) and tannins in the wine. Efforts to increase tannin levels are most successful at the winery level, although some research found that low-vigor vines within an individual vineyard had higher grape-tannin levels.

No relationship has been found between tannin levels of fruit and tannin concentration in the resulting wine. It is difficult to predict tannin extraction from fruit ripeness or maturity, but earlier research2,3,4,5 found that winemakers can manipulate tannin extraction through extended maceration (minimum of 20 days needed to see differences), increased fermentation temperature (keep as warm as conditions allow without killing yeast) and higher alcohol (an increase of 2%-3% above normal winemaking practices).


This article was condensed from the report “Effects of Berry Maturity and Wine Alcohol on Phenolic Content during Winemaking and Aging,” published in the American Journal of Enology & Viticulture, January 2018.

Dr. Caroline Merrell was a post-doctorate research associate in the Viticulture and Enology Program of Washington State University, where she focused on wine chemistry and sensory research. She recently joined California’s Jackson Family Wines as a research and development chemist.

Melissa Hansen, research program manager for the Washington State Wine Commission, works to make viticulture and enology research supported by the Washington wine industry more accessible to the state’s winemakers and grape growers. Hansen spent nearly 20 years as a journalist for Good Fruit Grower magazine and was involved with California’s table-grape and tree-fruit industries for 15 years.

References
1. Sacchi KL, Bisson LF and Adams DO. 2005 A review of the effect of winemaking techniques on phenolic extraction in red wines. Am. J. of Enology & Viticulture, 56: 197-206.
2. Harbertson JF, Kennedy JA and Adams DO. 2002 Tannin in skins and seeds of Cabernet Sauvignon, Syrah and Pinot Noir berries during ripening. Am. J. of Enology & Viticulture, 53: 54-59.
3. Singleton VL and Drape DE. 1964 The transfer of polyphenolic compounds from grape seeds into wines. Am. J. of Enology & Viticulture, 43: 63-70.
4. Glawel R, Iland PG, Leske PA and Dunn CG. 2001 Compositional and sensory differences in Syrah wines following juice run-off prior to fermentation. J. of Wine Research, 12:5-18.
5. Casassa LF, Larsen RC, Beaver CW, Mireles MS, Keller M, Riley WR, Smithyman R and Harbertson JF. 2013b Impact of extended maceration and regulated deficit irrigation in Cabernet Sauvignon wines: Characterization of proanthocyanidin distribution, anthocyanin extraction and chromatic properties. J. of Agricultural & Food Chemistry, 61: 6446-6457.
6. Fulcrand H, Atanasova V, Salas E and Cheynier V. 2004 The fate of anthocyanins in wine: Are there determining factors? In Red Wine Color: Revealing the Mysteries. Waterhouse AL and Kennedy JA (eds.), pp 68-88. American Chemical Society.

 
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