Enology Notes

Enology Notes #81, September 9, 2003

To: Regional Wine Producers

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

Subject: Maximizing Aroma/Flavor and Structure in the 2003 Red Wines.

Enology Notes # 80 outlined some considerations in establishing a HACCP (hazard analysis and critical control point)- like plan. The following are some additional considerations to help maximize red wine aroma/flavor and structure from the difficult 2003 season.

Issues in Maximizing Aroma/Flavor and Structure:

1. Fruit Maturity. This year, there is a large degree of uneven ripening. To determine the extent of asynchronous development, collect 5 x 100 berry samples. Make sure the samples are taken properly. (See the web at www.vtwines.info, Vintners Corner, Vol. 16, No. 1.) Analyze each sample separately for something simple, such as Brix, and compare the difference among the samples. The greater the difference among samples, the greater the degree of uneven development. Uneven development suggests the importance of additional hang time, if the environmental conditions allow.

Shot Berries. This year we have a large number of shot berries in many of our red cultivars. The question is--what percentage of these green, undeveloped berries in the fermentor is acceptable? Given their high acidity, and immature skin and seed tannins, it is likely a small percentage will impact the wine. Your HACCP-like plan may suggest that shot berries are acceptable in some products, but not so in others.

2. Fruit Sorting. This year again highlights the importance of fruit sorting tables at the winery. It may be desirable to sort pre-destemming AND post-destemming, to help reduce the percentage of shot berries and stems.

3. Fermentable Nitrogen. The greater the degree of immature berries, the lower the concentration of fermentable N (alpha amino acids and ammonia). Because of the importance of N on fermentation and fermentation volatiles, it is desirable that the N status be determined before fermentation. (See www.vtwines.info, on-line publications, and Formol titration.) Remember, simply dumping DAP into the fermenter may INCREASE the production of H2S (see Enology Notes # 79).

Fermentation. With the potential for shot and other immature berries in the fermenter, adjustments in the wine production methodologies should be reviewed (see Enology Notes # 80).

The goal likely will be to limit the degree of extraction, particularly if the percentage of shot berries and immature fruit is high. Therefore, adequate sorting, destemming, limited crushing, cold soaking, use of a high polysaccharide-producing yeast, cool fermentation, very gentle cap management, and short vatting should be considered. For an excellent discussion of phenolic extraction in red wine production, see Kennedy and Peyrot des Gachons, Practical Winery and Vineyard, July/Aug. 2003.

4. Cold soaking, with or without the use of enzymes, may allow early dejuicing, thus avoiding excessive extraction (see short vatting, Enology Notes # 78).

5.Cool fermentation temperature will also limit the degree of extraction from shot berries. In a study we conducted some years ago, fermentations at 25 C (cap and juice temperature) gave 15% percent lower phenol extraction, vs. fermentation at 30 C. Deficiencies in the desirable tannins can be adjusted by tannin supplementation and/or fermentation with wood. Color extraction is also limited with cooler fermentation temperatures. This is a reason for considering conducting a pre-fermentation cold soak.

6. Yeasts which are high polysaccharide-producers may be an advantage in limiting the impact of harsh seed and skin tannins.

7. Gentle Cap Management. As has been outlined in previous issues, gentle cap management is essential.

Delestage. We have been conducting Delestage research since 1998. In several studies, we looked at the effect of Delestage (rack and return), with partial seed removal, on Merlot and Cabernet Sauvignon phenols, glycosides, and aroma compounds. In all of our studies, the fruit and wine had different pigment profiles. Following Merlot fermentations, the concentration of monomeric anthocyanins (un-polymerized pigments) was less in the Delestage lots by an average of 11.5 percent. By the completion of fermentation, small polymeric pigments (SPP) and, notably, large polymeric pigments (LPP) increased. The amount of LPP averaged 38 percent greater in the Delestage wines.

The increased conversion of monomeric pigments to LPPs results in increased color stability, and appears to correlate to an increase in the desirable mouthfeel we have noted in Delestage-produced wines. The wines have greater body, and lower tannin intensity, astringency, and bitterness. Each of these red wine palate components will be important area of concern this season.

Delestage was outlined by Dominique Delteil during his recent visit to Virginia. His presentation is posted on our website. See www.vtwines.info, click extension, then on-line publications. Some important points follow.

Delestage can be started as soon as the cap is formed, including during cold soak. First, the tank is completely drained, which allows the juice to have up to 4 g/L oxygen. Complete drainage is the key. The most concentrated juice is just below the cap. A pump over does not renew this juice, while a punch down does not fully oxygenate.

Complete cap drainage allows for optimum aeration, which results in optimum tannin polymerization, and desirable management of sulfur-containing compounds.

Juice return should be done with a low-pressure pump completely bathing the cap. It is essential that this be gentle enough not to cause mechanical damage to the cap, which would result in the extraction of non-soluble solids. Such solids can contribute to bitterness and astringency.

Delestage has several advantages. It provides the release of grape polysaccharides early and at a higher concentration (Delteil 2003). The early extraction of macromolecules, and their association with tannins, is important in integrating the palate structure and limiting the negative impact of aggressive tannins.

8. Short Vatting. The issues involved in short vatting were covered in Enology Notes # 78. Regardless of the cap management strategy, it must be gentle, and extremely gentle beyond mid-fermentation.

Some Virginia red wines are overly extracted. Their sensory characteristics are low volume (body), high acidity, high concentration of astringency, and excessive tannin intensity, with the presence of dryness and/or bitterness. These stem, in part, from too aggressive cap management, which increases harsh tannin extraction. After about mid-fermentation, cap management must be very gentle. Additionally, too much extraction decreases, not increases, aroma/flavor, providing a tomato leaf-like odor in wines such as Merlot.

Cool fermentation at 24-25 C, with Delestage done only during the first 5-8 degree Brix drop, can give the same color and a better mouthfeel than fermentations at 30 C. Additionally, gentle cap management can provide fresher varietal aromas.

The possible benefits of yeast fining, thermal vinification and microoxygenation for structural modification of the 2003 vintage red wines will be reviewed in subsequent issues.

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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