Enology Notes

Enology Notes #76, July 3, 2003

To: Virginia Wine Producers

From: Bruce Zoecklein, Head, Enology-Grape Chemistry Group, Virginia Tech

Subject: Upcoming Enology Extension Programs: Mouthfeel Management, Wine Micro/Sulfur-containing Compounds, Cabernet Franc, Norton Roundtable

1. Mouthfeel Management. Winemaker Technical Roundtable - July 15, White Hall Vineyards, 1:00 p.m. - 4:30 p.m.

Dominique Delteil will be our guest. Dominique is the director of research and development for the Interprofessionalle Cooperaty du Vin in Montpellier, France. Dominique has conducted research on yeast selection, tannin management and mouthfeel. He and I will lead a discussion on mouthfeel management, including sensory evaluations involving yeast selection. At the meeting, we will review and discuss a number of topics related to mouthfeel.

Pre-registration required. Please send an email note to Terry Rakestraw at rakestra@vt.edu with "Technical Roundtable" in the subject line, and your name, company and phone number in the body of the email.

Mouthfeel balance is a critical feature influencing wine quality, by impacting the harmony and integration of structural components. The major factors governing palate balance in dry wines are the quantity and "quality" of tannins, concentration of alcohol, and concentration and types of acidity (see Enology Notes #68 and 69).

Mouthfeel issues. Wine mouthfeel is made in the vineyard (see Vintner's Corner Vol. 12, No. 1, 6). Vineyard row orientation and canopy management can influence both heat and light into the canopy. For example, fruit on the southern side of east-west rows receives more light and heat.

Heat and light interception can have an important influence on fruit chemistry, as we and others have seen. Based solely on the side of the canopy, we have noted a 31% difference in Cabernet Sauvignon skin tannin per berry. We have also noted differences in skin pigment components: a 13% difference in total skin color per berry, and a 43% difference in the concentration of small polymeric pigments (SPP) in the skins (small molecular weight tannins associated with anthocyanins). These changes have been noted in the absence of differences in degrees Brix (see Enology Notes #68).

Maturity. Maturity of skin and seed tannins is required for optimum mouthfeel of red wines. This requires adequate sampling and sample evaluation (see Enology Notes #53). The uniformity of fruit sampling will be an important issue this season, due to our environmental conditions during bloom. Poor set can influence the degree of uneven ripening. This could have a negative impact on mouthfeel, and should be assessed by evaluating the variation among berry samples taken from a given vineyard block.

Processing. The important question to ask is how to extract the desirable color and mouthfeel components during the early stage of processing, and how to avoid over-extraction. Production issues such as cold soak (see Vintner's Corner Vol. 13, No. 2) and enzyme addition have their place.

Yeast selection will be discussed at the Roundtable, and we will have samples for sensory evaluation (see Vintner's Corner Vol. 12, No. 5).

Delestage. For several seasons, we have evaluated a modification of the traditional rack and return procedures, as a means of modifying wine mouthfeel. In editions of the Vintner's Corner (Vol. 15, No. 3; Vol. 17, No. 3), I have discussed some of our work conducted at White Hall Vineyards with Brad McCarthy and Karen Vaillant.

More than half of the red wine tannins are extracted from the seeds during fermentation. This can have a large impact on mouthfeel if the seed tannins are not fully mature.

Anthocyanin pigments in grapes and wines are available in several forms. They are available as monomers or unbound compounds, and as those associated with other phenols, either small polymeric pigments (SPP) or large polymeric pigments (LPP). The SPP, along with monomeric anthocyanins, are extracted from the skin during winemaking, then the anthocyanin monomers and SPPs are incorporated into the LPPs. The result of this incorporation is to change the palate structure of the wine, and to help stabilize red wine color. It appears that the LPPs are related to soft, supple mouthfeel.

Our delestage research from the 2000 season suggests that this procedure reduced the tannin concentration by 35%, reduced the monomeric anthocyanins by 15%, and increased the polymeric pigments by 59%, compared to conventional fermentation lots. The LPP pigments are mainly formed during the winemaking and aging process, as a result of phenolic polymerization and incorporation of monomeric anthocyanins. The significant difference in the large polymeric pigment concentration, coupled with the reduction of seed tannins, helps to explain the sensory differences between delestage-produced and conventional punch-down fermentations. The delestage-produced wines are more fruit-forward, and have a richer, yet supple and integrated, tannin structure. Due to the higher percentage of LPP, it is assumed that the color stability of the delestage wines will be greater as the wines age.

Use of lees. During sur lie storage, yeast components, such as cell wall polysaccharides and, particularly, mannoproteins, are released into the wine. These macromolecules can positively influence structural integration, phenols (including tannins), body, aroma, oxygen buffering and wine stability (both protein and bitartrate).

Yeast-derived macromolecules provide a sense of sweetness as a result of binding with wood phenols and organic acids, aiding in the harmony of a wine's structural elements. The natural fining that occurs helps to protect against oxidation of certain fruit aroma compounds.

Consider utilization of light, 'clean lees' to enhance structural integration. Some use lees to increase the complexity of tank-stored wines. If you have such an interest, but are concerned with the potential of reductive tones, use lees that have been in barrels for two months or more. Such lees possess all of the desirable features, but are much less likely to cause reductive problems. Using 'barrel aged' lees is particularly important, if you intend to store sur lie in tanks greater than about 1000 gallons. The low oxygen concentration at the bottom of such tanks can create problems (see Enology Notes #6, 70 and 71).

Microoxygenation. This research was begun at Horton Cellars, and is tied in with a larger study involving California State University-Fresno and several California wineries, using wines produced with several different cultivars. A general discussion of microoxygenation was provided in my newsjournal The Vintner's Corner (Vol. 15, No. 2; Vol. 16, No. 6) and is available on my website.

We looked at the following sensory aroma/flavor attributes: Fruity, Green Tannin, Grit, Off Aroma, Oxidation, Tannin Plushness and Vegetative. These aroma/flavor and textural parameters were evaluated, compared to control wines.

Approximately 88% of the variability of the data (difference between control and treatment) is the result of two principal components, fruitiness and tannin plushness. In addition to the increased fruitiness and suppleness of the tannins, vegetative characteristics were substantially reduced by treatment.

2. Pre-Harvest and Wine Microbiology/Sulfur Compound Workshop, July 21, White Hall Vineyards, 9:30 a.m. - 4:00 p.m.

This day-long program will feature my colleague, Lisa Van de Water, The Wine Lab and Pacific Rim Oenology Service, and will cover practical issues with regard to wine microbiology and harvest issues.

Pre-registration required. Please send an email note to Terry Rakestraw at rakestra@vt.edu with "Wine Microbiology Workshop" in the subject line, and your name, company and phone number in the body of the email. There will be a $25 registration fee, payable at the door, to cover lunch plus expenses.

The formation of sulfur-containing compounds has been a winemaking problem for as long as wines have been produced. The problem remains, although our knowledge of the nature of the compounds, and the mechanisms influencing their control, is increasing. We will discuss some of the practical aspects outlined in Enology Notes #71 and 75.

3. Cabernet Franc Winemakers Roundtable, July 22, Blenheim Vineyards, 1:00 p.m. - 4:00 p.m.

We will discuss the recent visit to the Loire Valley, talk about the proposed study tour to the Loire Valley in March 2004, and taste Cabernet Franc wines from Chinon, Bourgueil, St. Nicholas - de-Bourgueil and Saumur-Champigney.

Some of the topics listed in Enology Notes #75 will be discussed. Please bring a cellar sample or bottled Cabernet Franc. RSVP required. Please send an email note to Terry Rakestraw at rakestra@vt.edu with "Cab Franc" in the subject line, and your name, company and phone number in the body of the email.

4. Norton Roundtable, July 28, Chrysalis Vineyards.

The third annual Norton Roundtable meeting will be conducted at Chrysalis Vineyards, beginning at 1:00 p.m. This meeting is for current Norton grape growers and winemakers. RSVP required. If you are interested in attending, send me an email message at bzoeckle@vt.edu.

Subscription to Enology Notes. All past Enology Notes and Vintner's Corner newsjournals are posted on the Enology-Grape Chemistry Group's web site at: http://www.vtwines.info/. Enology Notes are slightly different in content from the subscription based Vintner's Corner newsjournal.

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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
Email: bzoeckle@vt.edu