No. 6 November - December, 2003
Bruce W. Zoecklein
Department of Food Science and Technology
VPI & SU - 0418
Blacksburg, VA 24061
Web site: http://www.vtwines.info/
Table of Contents
I. Structural Balance and Mouthfeel
One of the current winemaking challenges is to determine how best to deal with the structural/mouthfeel disbalance in some of our 2003 red wines. For reasons outlined in previous editions, this season resulted in generally high TAs, notably high malic acid concentrations, and immature tannins. Each can contribute detrimentally to structural balance and mouthfeel. The following is a review of some of the important issues, and several post-fermentation recommendations. Generally, structural balance can be viewed in the following relationship that I have called the palate balance equation.
Sweet <--> Acid + Phenolics. This inverse relationship suggests that an increase in the perception on one side decreases the perception of components on the other. The converse is also true. With this in mind, it is easy to understand how the specific components of wine mouthfeel interact. The sweet elements in a red wine include carbohydrates, polysaccharides and ethanol. The acid elements are grape-derived organic acids. The phenolic elements in the above relationship include components which impact the tannin intensity, astringency, bitterness, and dryness, as described by Delteil, 2003.
Sweet. In a dry red wine, the sweet elements are frequently not perceived as sweet, due to the impact of the acid and phenolic elements. These so-called sweet elements do still contribute to the perception of body or volume.
Again, as the components on the right side of the palate balance relationship are quantitatively or qualitatively reduced, body or volume increases. This is one reason for the interest in microoxygenation. The polymerization of tannins reduces their intensity, and usually their astringency, resulting in an increased perception of the sweet elements. The converse is also true. If the phenolic load increases as a result of oak extraction, for example, there is a resultant decrease in the perception of body.
Acidity. Acidity usually increases the perception of the phenolic elements, including tannin intensity, astringency, bitterness, and dry tannins. Increases in acidity decrease the perception of body, or the left side of the palate-balance relationship. The converse is also true, as the polysaccharide concentration (from grapes, yeast, bacteria, or commercial products) is increased, the perception of acidity is reduced.
Tannin Intensity and Astringency. Tannin intensity and astringency follow the relationships for phenols shown above. In addition, these sensory responses to phenolic elements are increased with the presence of VOCs (volatile sulfur compounds, see Enology Notes #70, 71), the presence of herbaceous components, and suspended yeasts and bacteria.
In our trials on the use of microoxygenation, we have seen a reduction in both tannin intensity and astringency, in part, due to the reduction in red wine herbaceousness.
As a practical note, the evaluation of young red wines, particularly from 2003, is best done on a sample where there is adequate clarification to remove a large percentage of the suspended yeast/bacterial cells, because the perception of the phenolic elements may be higher in a clarified sample (Delteil, 2003).
Most things are not as simple as they appear, including the palate balance relationship. Alcohol is a major contributor to the sweet elements in a wine. Up to about 14%, it reduces the perception of acid and phenolic elements (Delteil, 2003). Beyond that level, it can enhance the perception.
Dry Tannins and Bitterness. These sensations are a tactile response, and true taste, respectively. Both can contribute to a red wine’s finish, sometimes positively, however, frequently not. Dry or dusty tannins, and those that contribute to bitterness, are phenols which have certain size and structural qualities. The perception of dry tannins and bitterness is not necessarily correlated to carbohydrates or polysaccharides. This is due to the nature of these phenolic elements, and how and where they are perceived by the palate. These phenolic-derived sensations are also positively correlated with VOCs, herbaceous compounds, and suspended yeasts.
One of the true difficulties this season is that both dry tannins and bitterness perceptions are increased with high levels of malic acid. Most of our red grape varieties this season came in with elevated to very-high levels of malic acid.
Post-fermentation Modification. What are the steps that can be used to help improve post-fermentation structural and mouthfeel balance? Unfortunately, the options are not nearly as extensive post-fermentation as pre-fermentation. These include biological and non-biological deacidification, fining, including yeast fining, addition of compounds such as gum Arabic, thermal processing, microoxygenation and sur lie storage.
II. Sur lie
As has been previously suggested, it is important not to overlook the power of macromolecules. Polysaccharides are found in wines at concentrations ranging from 300-1000 mg/L. They are of two general types, those found in the fruit, such as pectins, and those produced by yeast and bacteria during fermentation and released during autolysis. A number of compounds classified as polysaccharides also have significant protein components, and vice versa. The yeast cell wall is composed largely of ß-glucans and mannoproteins. Mannoproteins are released during sur lie storage. This release post-fermentation is the result of enzyme hydrolysis of the lees caused by ß-glucanases, present in the cell wall. This enzyme retains activity for several months after cell death, releasing mannoproteins into the wine. This increase can be as much as 30% in four months of aging sur lie. Heavy lees contact results in a high concentration of polysaccharides, compared to light lees; the difference can be as much as 200 mg/L (Ribereau-Gayon et al., 2000). Lees contact can have a major impact on structural balance. Polysaccharides have the ability to bind with phenols, thereby lowering the perception of the tannin elements and, therefore, acidity. The impact of polysaccharides on astringency is evidenced by a reduction in the gelatin index (see Zoecklein et al., 1995). This reduction can cause an increase in the wine’s volume or body. Lees contact is particularly effective at modifying wood tannin astringency by binding with free ellagic tannins, thus lowering the proportion of active tannins. Sur lie storage can reduce the free ellagic acid by as much as 60%, while increasing the percentage of ellagic tannins bound to polysaccharides by 24% (Ribereau-Gayon et al., 2000).
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