Enology Notes

Enology Notes #110, January 9, 2006

To: Regional Wine Producers

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

Subject: Tannin and Color Management and Measurement Short Course; Virginia Tech Enology Service Lab Update; Untypical/Atypical Aging; Sixth International Cool Climate Symposium

I. Tannin and Color Management and Measurement, an Advanced Short Course.  The Enology-Grape Chemistry Group will offer a one-day advanced Tannin and Color Management and Measurement short course February 27, 2006, at White Hall Vineyards, beginning promptly at 10:30 a.m.  We have some common beliefs regarding grape and wine phenols. Are they true?

  • Grape and wine color strongly correlate to aroma/flavor?
  • Anthocyanin concentration strongly correlates to aroma/flavor?
  • Color is a good indicator of yield?
  • Aged red wine color is directly related to young wine color?

This practically-oriented, advanced program will explore the influences of various phenolics which could/should be monitored, and how they are monitored.

Sensory analyses will be highlighted, and chemical analyses that can be conducted at the winery will be discussed and compared.

The topics will include the following:

Grape and wine phenolic compounds

  • Types and classes of phenols
  • Grape-derived phenols
  • Processing-derived phenols

Nature of grape and wine color

  • Hyperchromicity/copigmentation
  • Color stability

Viticultural factors impacting grape phenolic compounds, including color

  • Cultivar/rootstock/clone
  • Vine nutrition
  • Climate: macro-, micro-
  • Yield
  • Maturity

Enological factors impacting phenols

  • Cold maceration
  • Short vatting, Australian red, extended maceration
  • Délestage
  • Enological tannins/wood fermentation
  • Thermal processing, impact of temperature
  • Fining

Sensory analysis techniques, with the following examples

  • Phenolic standards
  • Délestage vs. cap punch
  • Short vatting vs. extended maceration
  • Total vs. partial destemming
  • Yeast strains
  • Terroir effects

Phenolic measurement at the winery

  • Wet chemistry and spectrophotometric procedures will be compared.
  • Measurements, such as tannins, color density, hue, total pigments, polymeric pigments, copigmented anthocyanins, etc., will be outlined, and their significance discussed.

Pre-registration is required BEFORE Monday, February 20, 2006.

COST: $45 per person, due by Monday, February 20, 2006.

Make checks payable to: Foundation Account, Virginia Tech.

Mail to: Terry Rakestraw
Department of Food Science & Technology
Virginia Tech - 0418
Blacksburg, VA 24061

Please bring a bagged lunch, since food will NOT be provided. 

II. Virginia Tech Enology Service Lab.  The Enology-Grape Chemistry Group at Virginia Tech is establishing a fee-based, full-service enology laboratory. This lab will provide chemical, physical, microbiological and sensory analysis, including standardized reagents.

This service will be available to wineries in any state, and to importers and wholesalers. The prices will be competitive, with profits designed to help support extension activities of the Enology-Grape Chemistry Group.

We are pleased to announce the hiring of Ken Hurley, who will act as lab director. Ken has an extensive background in biochemistry and laboratory instrumentation, and will be working to get this lab service as fully automated as possible.

The goal of this analysis program is to provide very rapid turn-around, with optimum precision and accuracy. Look for details regarding this service in upcoming issues of Enology Notes.

III. Untypical /Atypical Aging. Grape nitrogen appears to be related to a sensory phenomenon known as untypical (UTA) or atypical (ATA) aging. This topic has been reviewed in previous editions of Enology Notes (#14, 77, 107).  Some Virginia vineyards experienced moisture stress conditions in 2005, that may increase the incidence of ATA in wines produced from those vines.

Wines with this taint lose varietal character very early, and develop atypical aromas and flavors, described as naphthalene (moth balls), dirty dish rag, wet towel, linden, floor polish, etc., and are characterized by an increase in a metallic-like bitterness. As discussed during our Volatile Sulfur Compound Workshop, ATA can also be associated with an increased production of post-bottling reductive-odor defect.

First reported in Germany, ATA has been identified in other European wine-producing regions, the Pacific Northwest, California, and the eastern US. This sensory problem has been associated with vine stress, impacting nitrogen metabolism.

Nitrogen deficiency induced by vine stresses, particularly at bloom and véraison, appears to be linked to this problem. As such, ATA occurs more frequently on dry vineyard sites and in dry years.

A number of studies have concluded that different cultivars have different nitrogen requirements, and that increasing the amino acid concentration of the fruit can produce more desirable aromas and flavors. We do not know the desirable levels and proportions of amino acids in the fruit, or methods to achieve those levels. We do know that nitrogen stress appears to increase the incidence of ATA.

Several studies suggest the benefits of irrigation with regard to nitrogen uptake. Optimum soil moisture helps assure adequate N uptake and maintenance during bloom, and optimum photosynthesis during véraison.

Sponholz (2001) reported that N application and cultivation of vineyard floors reduced ATA development. Moisture stress conditions, in general, may not allow for optimum aroma/flavor compound formation, by slowing the rate of fruit maturation. This, coupled with metabolites that appear to be unique to ATA, results in limited varietal intensity and the production of detrimental sensory features.

The characteristic ATA odor was originally thought to be caused by certain metabolites (o-aminoacetophenone, skatole or indole), but studies conducted by Dr. Thomas Henick-Kling and his colleagues, of Cornell University, would suggest otherwise.

We have seen ATA in Virginia. The following simple screening test for white wines, provided in Enology Notes # 77, is from Dr. Henick-Kling:

  1. Collect a sample of white wine and divide it into two aliquots of 100 mL or more each.  Label one as the control. Take the other sample of the same wine and add 150 mg/L ascorbic acid (Vitamin C). Label as treated.
  2. Pour samples into two bottles so that they are completely full, and seal well.
  3. Place both in an incubator set at 40ºC for 12 hours to 48 hours.
  4. Remove the samples, cool, and sensorially evaluate. If both wines smell and taste the same, the wine will likely not develop ATA. If the wine without ascorbic acid has changed aroma/flavor vs. the treated sample, it is likely it will develop ATA. 

This simple artificial aging test can be used as an ATA screen. If the test is positive, the best course of action is to prevent oxidation, and to add ascorbic acid to the wine after the free sulfur dioxide level has stabilized. Work done by Dr. Henick-Kling and colleagues suggest that ascorbic acid can delay ATA development by about two years. If you suspect your wines have ATA, contact my office.

IV. Sixth International Cool Climate Symposium. The Sixth International Cool Climate Symposium for Viticulture and Oenology is scheduled for February 5-10, 2006 in Christchurch, New Zealand. The theme for this event is Wine Growing for the Future. Keynote speakers will cover the following areas:

  • Managing viticulture and oenology for quality and sustainable outcomes
  • New technologies for cool climate wines
  • Marketing cool climate wines
  • Forging new frontiers and meeting new challenges

For additional details on the ICCS, see their website: www.iccs2006.org.nz.

Subscription to Enology Notes. All past Enology Notes newsjournals are posted on the Enology-Grape Chemistry Group's web site at: http://www.vtwines.info/.

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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
Cell phone: 540-998-9025