Enology Notes #107, October 7, 2005
To: Regional Wine Producers
From: Bruce Zoecklein, Head, Wine/Enology-Grape Chemistry Group, Virginia Tech
Some brief observations regarding this vintage:
Red Fruit. For most of the early part of the season, we had relatively rapid advancements in primary metabolites, specifically Brix . Most vineyards displayed good fruit quality potential, growth arrest, simultaneity of veraison, and uniformity of color.
Vineyards with low moisture reserves, over-cropped, or with insufficiently developed root systems (young vineyards), may have appeared to show some greater variability at veraison in mid- to late-season color variation.
Red Fruit Maturity. Some reported abrupt ripening stops, where degrees Brix have not increased. With the current rainfall, the slowdown in evolution may turn out to be reversible. However, some vineyards have fruit that display maturity imbalances.
This includes immature cap stem phenols (difficult to pick berries), incomplete color, gelatinous pulp, and immature skin and seed tannins.
A few varieties show signs of berry shrivel. Research indicates that the maximum rate of production of aroma/flavor compounds in Syrah fruit occurs at about the time when the berry stops importing water from the phloem or shortly thereafter. Therefore, maximum aroma/flavor occurs sometime after the berry reaches maximum weight. This may be true for other varieties. This is a good reason for monitoring the extent of berry shriveling. Changes also occur in the phenolic composition with shriveling, highlighting the importance of berry weight as a tool in stylistic winemaking (see Enology Notes #23).
Processing Considerations. An increase in the expected fruit pH evolution may be seen, notably in moisture-stressed vines. Most acidulate, when needed, pre-fermentation, to help assure palate integration.
Care must be used so as not to increase the aggressive or harsh tannin mouthfeel by excessive acid addition.
If immature tannins are present, consider early use of extraction enzymes and cold soak. This will increase the anthocyanin extraction vs. tannin phenols, notably if the pulp is gelatinous. This allows for gentle cap management, yet adequate color, mouthfeel and tannin intensity.
Use care in destemming. A high concentration of immature cap stems suggests the need for post-destemming sorting. This may be a requirement for consistent premium red wines in this region, and is always a good idea. This may be essential if the red must contains a high concentration of immature cap stems or jacks.
Fermentation temperature and length of maceration are means of modifying tannin vs. anthocyanin extraction. Naturally, decisions regarding both should be determined, based on fruit characteristics.
Moderate oxygenation post-dejuicing can aid in phenol polymerization and palate integration.
Nitrogen Status. We have observed relatively low fermentable nitrogen concentrations this season. This may be the result of the lack of soil moisture. There may also be some qualitative impacts. Vine stress causes an increase in the proline/arginine ratio, increasing the likelihood of reductive odor defect (see Enology Notes # 26, 70, 76, 79, and the slide show posted from our Volatile Sulfur Compound shortcourse at www.vtwines.info). It is essential that the fermentable nitrogen status be evaluated prior to fermentation (see Formol procedure under on-line publications at website). Recall that excessive N, as may occur by simply adding supplements including DAP without knowing the N status, may increase the likelihood of reductive odor defect.
ATA. As pointed out by Dr. Thomas Henick-Kling from Cornell University, there is a greater risk of ATA (atypical ageing) this season due to moisture stress. Moisture stress can influence the nitrogen metabolism in the plant, resulting in wines that rapidly develop oxidation-like features (see Enology Notes # 14 and 77). The Enology-Grape Chemistry Group will monitor this potential in Virginia.
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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