Getting Ready for Harvest – Part 3: Reducing “Green” Flavors in Red Wines

By: Denise M. Gardner

The “Getting Ready for Harvest” seminar featuring José Santos from Enartis Vinquiry (California) included a detailed discussion about the technical aspects of several key processes that are currently of importance to Pennsylvania winemaking. Some of these topics included:

  • White wine oxidation protection
  • Yeast nutrition and its importance during fermentation
  • Reducing “green” aromas and flavors in red wines
  • Color stability in red wines

In this four part series, I will summarize some of the discussions led by José during the 2014 “Getting Ready for Harvest” workshop.

Generation of “Green” Flavors in Wine

Immature grapes concentrate green flavors in berry skins. Methoxypyrazines, in particular, act as repellants to potential predators that may attempt to eat the berries prior to ripeness. After veraison, berries begin to increase sugar concentrations and redistribute methoxypyrazine flavor compounds to green matter throughout the vine. In exchange, many aromatic, varietal flavor compounds develop in the berry skin. However, some varieties (like Cabernet Sauvignon, Sauvignon Blanc, and Cabernet Franc) have a higher prevalence of retaining some of these green flavors, and the characteristic “green bell pepper” flavor has become synonymous with these and other varieties’ varietal character.

Additionally, several other flavor compounds can be responsible for green-related aromas and flavors. For example, the aldehyde hexanal is commonly associated with a “green grass” or “veggie” aroma/flavor. Previous research at UC Davis  has shown that the presence of these green-related aromas masks, or subdues, the perception of fruit aromas and flavors in wine.

Unripe, green grapes.

Unripe, green grapes.

In some years, especially in cool-climate regions, ripening may be very dependent on weather conditions. Grape flavor development, referred to as the engustment stage in ripening (Coombe and McCarthy, 2000), occurs well after sugar ripeness has been established. The engustment stage lasts only for a few days, dependent on variety, before flavor compounds begin to break down into post-ripening flavors (i.e. prune juice, raisin-like). This is one of the reasons why learning berry sensory analysis for vineyard sampling can be an essential and critical tool for growers and winemakers trying to make premium wines.

Techniques Associated with Reducing Green Flavor in Wine

Some wine experts discuss the potential to integrate green (and Brettanomyces-produced) flavors into red wines through tannin and reductive strength. Clark Smith’s recent book Postmodern Winemaking discusses this topic at length.

José discussed two other options available for wineries to tinker with during production: eliminating or minimizing the concentration of green flavor compounds during production, or masking their aroma and flavor by enhancing the fruit characteristics.

One way to try to minimize green aroma and flavor is through fast and hot fermentations, in addition to decreasing the maceration time, which allows for less extraction of these compounds. Starting a red wine fermentation at the optimum 75-85°F allows for adequate extraction of tannins and color compound. Wine should remain at this temperature for at least 24 hours prior to ramping up fermentation temperature to about 90-95°F. This temperature should help “blow off” some of those green-related flavors retained in the red wine. Of course, volatility of flavor compounds is non-specific, and winemakers should be aware that they will lose other fruity aromas as well. Bring the fermentation temperature back down to 75-85°F to finish (to limit the toxicity of ethanol at higher temperatures), which produces optimum conditions for red color stability management practices. This will also help retain the remainder of aroma and flavor left in the red wine.

Vigorous red wine fermentation.

Vigorous red wine fermentation.

Additionally, winemakers can opt to use enological products that help enhance the red fruit characters of wine. Through fermentation, winemakers should choose yeast strains that have a high ability to produce secondary byproducts related to aromas and flavors. Yeast strains that highlight enhanced aromatics beyond varietal character should be considered.

Additionally, yeast nutrition is essential for these fermentations. Yeasts will need an adequate amino acid supply in order to produce a variety of fruity aromas and flavors. Amino acids offer the backbone structure for many aromatic compounds. Having a pool of many different amino acids, allows for a multitude of aromatic compounds to be produced during fermentation. José highlighted that several amino acids in particular are essential for aromatic compound synthesis: valine, methionine, cysteine, leucine, isoleucine, histidine, phenylalanine, alanine, and tyrosine. These amino acids are contributed by the Enartis line products Nutriferm Arom and Nutriferm Arom Plus, which are added at yeast hydration or inoculation. For more information related to yeast nutrition, please visit the Part 1 blog post to this series.

Finally, José introduced a product line of tannins that offer aromatic precursors, which exist in a non-aromatic form until chemically rearranged. Specifically, he discussed the use of Enartis Tan Red Fruit, which contains condensed tannin and glycol-conjugated nor-isoprenoids (a precursor to the nor-isoprenoid flavor compounds) sourced from cherry wood. Additions of these types of tannins can help increase the concentration of fruit-based aromas and flavors, and enhance a wine’s fruity character.

Practicality to Production

While all of these products offer some practical solutions, it is essential that these winemaking steps are considered with purpose in the winery. Winemakers are presented with a plethora of enological products, and should approach each new product on a trial basis to ensure that it works for the winery. As a research, I would have to encourage wineries to leave a control (i.e. a batch of the same wine without use of the product) to evaluate the quality of the new product addition. If additions are made post-fermentation, always do bench trials.

Harvest is an incredibly busy time for the winery. It is helpful if wineries have standard operating procedures (SOPs) in place for incoming fruit in various quality categories. For example, red grapes with high sugar and flavor ripeness should be treated differently during fermentation compared to red grapes with low sugar and flavor ripeness or high sugar and low flavor ripeness. Red grapes with higher quantities of disease should also have a different fermentation plan. Determining the wineries fermentation procedures for various types of fruit, and distributing that information among cellar employees, can help get everyone on the same page prior to harvest. This practice also releases the tension caused by “on-the-fly” decisions that may not be practical or optimum for a given variety or lot of grapes.

Finally, when implementing new procedures in the winery, winemakers should take extra care to develop them. It may take a few years, for example, for winemakers to become comfortable with high mid-fermentation temperatures in red wines that have a higher prevalence of green flavors. Taking adequate notes of the process can be helpful in recalling what worked and what did not work during that particular harvest season.

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