Wines Enology Grape Chemistry Lab at Virginia Tech

Enology Notes

Enology Note #90 June 9, 2004

To: Regional Wine Producers

From: Bruce Zoecklein

Subjects: Red Wine Production Considerations and Norton Roundtable; American Society for Enology and Viticulture Annual Meeting and Symposium

Red Wine Production Considerations and Norton Roundtable Meeting. We will conduct a Norton Roundtable meeting July 26, 2004 at Chrysalis Vineyards at 1:30 PM. If you are interested in attending, RSVP to by July 22.

The following is an outline of some Norton and other red wine production considerations. VC stands for Vintner’s Corner, and EN for Enology Notes. All past VC and EN publications are indexed and posted on my website at

Unique Features of the Norton grape:

  • low tartaric/malic ratio
  • high concentration gallates and diglucoside pigments and mix,
  • surface to volume ratio, berry size and seed #, volume/size

Production Challenge:

  • structural/textural balance
  • The seven components of importance in structural/textural balance include: volume (body), acidity, roughness, tannin intensity, astringency, dryness and bitterness.

Structural/Textural Quality: the result of :

  1. the quantity and quality of phenolic components in the fruit,
  2. the interaction and stabilization of anthocyanins, tannins and certain polysaccharides, and
  3. TA and the sense of sweetness.

Structural balance can be viewed as follows:

Sweet <--> Acidity + Bitterness and Astringency

In this relationship the sweet elements of a wine (derived from alcohol, polysaccharides, etc. must be in relative balance with the sum of the acidic elements and phenolic elements (both astringency and bitterness).

Thus, the higher the TA, the lower the desirable phenolic load for balance. A wine with a high level of sweet elements (e.g. alcohol) can support a higher level of TA and phenolic elements.

Structural balance is similar to the concept of Suppleness Index. Suppleness Index = Alcohol-(Acidity + Tannin)

The ratio of bitterness to astringency helps to explain the concept of hard vs. soft tannins. The interaction of phenolics and other wine components is an important feature in wine texture. Even experienced tasters have trouble differing between bitterness and astringency. Suggest running in-house trials:

Astringency - alum, gallic acid, tannic acid, citric acid, and mixtures. Bitter - caffeine, quinine sulfate.

Norton Style: (VC, 11:4,12:2, 14:1 EN#4) Style and textural quality are influenced by quantity and quality of phenols, phenolic maturity, extraction/management, and interaction with other structural elements (acids, polysaccharides, peptides, sugars).

Varietal Descriptors: spicy, jammy, earthy, dusty, black pepper, black raspberry, mushrooms, spice, cloves, nutmeg, tobacco, chocolate.

Key Questions: (VC 14:5) What vineyard management tools are available to influence aroma/flavor and phenols? How can we monitor the quantitative and qualitative changes in aroma/flavor and phenols in the fruit and the wine? What are appropriate concentrations and proportions of aroma/flavor phenols for specific wine styles, and what production methods will reach our stylistic goals? Answer - establish a HACCP-like plan.

Establish a HACCP-Like Viticultural and Enological Plan (VC 12:6,15:1, 15:2, EN# 8, EN #19)


Norton Vine Nutrition

Training and Trellising

Canopy Management (VC 12:1, 14:1)

  • optimum degree of fruit shading
  • optimum degree of leaf shading
  • influence of canopy management on structural balance, e.g. TA, tartaric/malic acid and phenols
  • influence on asymmetric ripening
  • influence of row orientation

Vine Stress (VC 12:1)

  • soils and soil pH
  • Mg++ nutrition vs. soil concentration
  • monitoring nutritional status
  • correcting Mg++ deficiencies
  • crop load

Vigor Control/Management

  • shallow soils/low vigor

Defining Optimum Crop Load (VC 12:1, 15:5)

  • vine balance
  • avoid delaying maturity

Fruit Ripeness Indicators (VC 11:4,12:1,12:5, 12:6, 16:1, EN#53)

  • goal driven
  • indicators should correlate to aroma/flavor and phenol suppleness
  • fruit sampling methods
  • degree of asymmetric ripening: clusters, berries. Sugars are usually fairly uniform (small coefficient of variance, secondary metabolites can be much greater)
  • sensory evaluation of skin, stem, pulp and seed phenolic maturity
  • chew skins, use phenol descriptors (see Mouthfeel Wheel)
  • seed maturity - color, texture and brittleness
  • anthocyanin content and maturity
  • evaluate crushing ability
  • relationship between berry weight, shriveling, and engustment
  • relationship between berry weight and physiological maturity
  • berry softness and diffusion of pulp
  • estimation of berry size (EN#23)
  • measurement of color
  • sugar per berry
  • relationship between days post-bloom and maturity
  • seed numbers and seed maturity
  • pH, Brix, TA (EN#6). Brix and aroma/flavor, phenol development are not the same. Changes in pH are not necessarily a function of berry ‘age’, and relate to K+ and vigor. Tartaric/malic ratio low
  • Brix to alcohol conversion rate
  • phenol maturity, TA, and potential structural balance

Harvest Methods

  • hand vs. mechanical


Processing (VC 14:1)

  • should be site driven and goal driven: integration and balance of structural elements, conversion of monomeric anthocyanins to large polymeric anthocyanins. Avoid the extraction of ethanol-soluble hard tannins

De-stemming/crushing/whole cluster press

  • planning maceration - know the extent of mechanical resistance from various parts of the fruit
  • importance of gentle fruit handling, low non-soluble solids to wine integration
  • degree of berry breakage

Cap Management Procedures

Cold Soak (VC 13:2)

  • enhance ‘bright fruit’ character, increase color stability
  • time/temperature
  • w/o enzymes
  • w/o sulfur dioxide
  • w/o oxygen

Bleeding/Co-fermenting (EN#3)

  • bleed juice has lower arginine/proline ratio which will influence pH evolution

Delestage (Numerous issues of VC and EN)

  • This may be the most important varietal in Va. for this processing method. Grape seed tannins differ from skin tannins, in that they contain a higher concentration of monomeric flavan-3-ol, and those which have esterified to gallic acid. As such, they are very harsh and bitter. Delestage can remove as much as 40% of these seed tannins.

Fermentation (VC 14:2, 14:4, 15:4)

  • Brix to alcohol conversion rate/Chaptalization
  • alcohol and structural balance
  • must TA, tartaric/malic ratio, pH
  • TA reduction methods
  • tannin addition, can add mid-palate depth
  • fermentable nitrogen, not a matter of simple fermentation sticking (VC 13:4,14:2, 14:4)
  • yeast(s), high malate reducer, high polysaccharide producer, high tannin absorber, fermentation rate(VC 13:3). Common yeasts include 71B, BM45, D254
  • sulfur dioxide, polyphenol oxidase, phenol polymerization (VC 13:4)
  • role of oxygen (VC 16:3)
  • size and shape of fermentation tank
  • open vs. closed
  • temperature of liquid and cap
  • MLF, strain(s), timing, volume of inoculum
  • w/o wood (VC 14:3)
  • punch down, pump over, irrigation systems, sweeper tanks, delestage (VC 15:3, EN#8)
  • alcohol at time of dejuicing (VC 13:2)
  • post-fermentation maceration
  • free run vs. press run

Cellar Management for Norton

  • wood(s): sources, seasoning age, fill age, barrel type, etc.
  • lees (VC 14:3, EN#6), very helpful for structural integration
  • sulfur dioxide, keep low (15 mg/L free) for first year (VC 12:2, 13:5, 14:6)
  • oxygen, first year process oxidatively, thereafter anaerobically
  • measure oxygen pick-up (VC 12:3, 13:5, 14:3)

Maceration enzymes may be desirable, particularly if you have a lot of whole berries in the fermenter. Enzymes contain pectinase, hemicellulases and cellulases which, like native enzymes, aid in the diffusion and association of anthocyanins, tannins, and polysaccharides.

Yeasts. Species and strain have a significant influence on grape and wine phenols, as a result of binding and polysaccharide liberation, and reduction in TA. Desirable strain features include: 1) low color absorption, 2) a high production of manno-protein polysaccharides available during fermentation and autolysis, 3) malate reducer, and 4) a low production of volatile sulfur compounds (some of which can enhance the perception of astringency).

Cap Management should occur to limit seed tannin extraction and the formation of non-soluble solids. Process to encourage phenolic polymerization and stabilization (oxygen exposure and low sulfur dioxide). Delestage reduces seed extraction, enhances enzyme activity and oxidative polymerization.

Tannin Management and Textural Quality. Tannin quality (suppleness, creaminess) is the result of : 1) the quantity and quality of phenolic components in the fruit, 2) the interaction and stabilization of anthocyanins, tannins, and certain polysaccharides, and 3) TA.

Integration. During fermentation, yeast species and strain, oxygen, and maceration influence the stability of phenols and their resulting mouthfeel. What is the sensory significance of specific phenols, including specific tannins? All phenols are both bitter and astringent. Bitterness is the result of access to membrane-bound receptors and is likely limited by molecular size.

Bitterness and astringency increase with increased molecular weight. Polymerization increases astringency due to an increased number of possible hydrogen binding sites.

With concentration, the bitterness of monomeric flavonoids increases at a faster rate than the astringency. This is in contrast to the astringency of polymeric seed tannins, which increases more rapidly than bitterness, with increases in concentration. Astringency masks bitterness, an extremely important concept to understand as it relates to fining.

Post-fermentation microoxygenation. This technique is ideally suited to a variety such as Norton, which has a high concentration of hard/harsh tannins. See numerous issues of Vintner’s Corner and Enology Notes.

Post-fermentation blending

  • filtration and wine quality (VC 16:2)

American Society for Enology and Viticulture Annual Meeting and Symposium. July 13-16, 2004, Hotel Roanoke, Roanoke, VA. The underlying goal of the symposium is to explore how soils, climate (particularly temperature), and cultural practices affect fruit and wine composition and quality. Presentation topics include the impact of viticultural practices on grape and wine quality (Kees van Leeuwen, Professor of Enology at Bordeaux Agricultural University, and viticulturist, Cheval Blanc; Andrew Reynolds, Professor of Viticulture at Brock University in Ontario; Phil Freese, viticultural consultant, WineGrow), climate indices used to predict grape and wine quality as a function of grape variety and environmental interaction (Erland Happ, Happs, Pty. Ltd., Western Australia; Zelma Long, Zelma Long Wines; Greg Jones, Professor of Geography, Southern Oregon University), and to explore the role of soil physical properties on grape and wine quality (Kees van Leeuwen). Symposium conveners are Professors Tony Wolf and Bruce Zoecklein of Virginia Tech. See you there!


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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:
Phone: (540) 231-5325
Fax: (540) 231-9293