To: Regional Wine Producers
From: Bruce Zoecklein, Head, Enology-Grape Chemistry Group, Virginia Tech
Subject: Apologies & Structural Balance and Mouthfeel
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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. Limiting new oak and Brettanomyces growth are also important in optimizing red wine mouthfeel and balance.
Each will be outlined in subsequent editions.
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Dr. Bruce Zoecklein
Professor and Enology Specialist Head Enology-Grape Chemistry Group
Department of Food Science and Technology, Virginia Tech
Blacksburg VA 24061
Enology-Grape Chemistry Group Web address: http://www.vtwines.info/
Phone: (540) 231-5325
Fax: (540) 231-9293