Enology Notes

Enology Notes #80, September 1, 2003

To: Regional Wine Producers

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

Subject: Enology Components of a Red Wine HACCP-Like Plan, Donations to Virginia Tech.

The following is a HACCP (hazard analysis critical control point) outline for red wine production. In the outline, VC stands for Vintners Corner, and EN for Enology Notes, two publication series available on-line at www.vtwines.info. Click extension, then either Vintners Corner or Enology Notes.

For additional information on HACCP, also see on-line index on our web site. (We have separate indices for both Enology Notes and Vintners Corner. Ed.)

1. Enology Components of a Red Wine HACCP-Like Plan

Prior to the harvest, each of the following factors which influence wine structure/texture should be reviewed. How is each of these influencing your red wine structure/texture, aroma, flavor and overall quality?

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

Cold Soak (VC 13:2)

Bleeding/Co-fermenting (EN #3)
Bleed juice has lower arginine/proline ratio, which will influence pH evolution

Delestage (Numerous issues of VC and EN)
Grape seed tannins differ from skin tannins, in that they contain a higher concentration of monomeric flavon-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. With or without seed removal this gental cap management method can increase phenol polymerization.

Cellar Management

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

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 adsorption,
  2. high production of mannoprotein polysaccharides available during fermentation and autolysis,
  3. malate reducer, and
  4. low production of volatile sulfur compounds (some of which can enhance the perception of astringency).

Cap Management
Should occur to limit the formation of non-soluble solids and seed tannin extraction. Process to encourage phenol polymerization and stabilization (oxygen exposure and low sulfur dioxide). Delestage reduces seed tannin extraction and enhances 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.

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 some varieties which have a high concentration of hard-harsh tannins.

Post-fermentation blending
Filtration and wine quality (VC 16:2)

Fermentation of Red Wines with Wood
There are two types of wood fermentation used in red wine production, the Australian Red method and fermentation with cubes or staves. The Australian Red approach, so named due to its origin, involves several steps. Crushed and destemmed fruit is cold soaked with maceration enzymes for 24 to 48 hours. Cold soaking is effective in aiding the extraction of anthocyanins and stabilizing color. Additionally, co-pigmentation promoters are extracted. Wine is dejuiced at 18-16 °Brix, depending upon the initial maturity, and barrel fermented. The alternative is to add cubes (not chips) to the fermentation.

During wood fermentation, two factors help to influence the structural integration of the wood. Mannoproteins are released by the yeast, which help to bind phenols. Additionally, yeast adsorb about 1/3 of the ellagic tannins, lowering the perception of astringency. The process of wood fermentation is used by some to create wines for blending.

Sur lie and structural component integration
As has been previously suggested in several Enology Notes, do not overlook the power of macromolecules. Polysaccharides are found in wines at concentrations ranging from 300-1000 mg/L. They are of two general types, those found in the fruit, such as pectins, and those produced by yeast and bacteria during fermentation and released during autolysis. A number of compounds classified as polysaccharides also have significant protein components and vice versa.

The yeast cell wall is composed largely of beta-glucans and mannoproteins. Mannoproteins are released during sur lie storage. This release post-fermentation is the result of enzyme hydrolysis of the lees caused by beta-glucanases, present in the cell wall. This enzyme retains activity for several months after cell death, releasing mannoproteins into the wine. This increase can be as much as 30% in four months of aging sur lie. Heavy lees contact results in a higher concentration of polysaccharides than with light lees; the difference can be as much 200 mg/L (Ribereau-Gayon et al., 2000).

Wine balance can be depicted as in the following relationship: Sweet<-->Acid + Phenolic Elements. This relationship suggests that as the perception of sweetness increases, the perceptions of those elements on the right-hand side of the equation will decrease. The converse is also true, as the sweetness diminishes, the perception of the acid and phenolic elements (bitterness and astringency) increases. Lees contact can have a major impact on structural balance. Polysaccharides have the ability to bind with phenols, thereby lowering the perception of both the tannin elements and, therefore, acidity.

The impact of polysaccharides on astringency is evidenced by a reduction in the gelatin index (see Zoecklein et al., 1999). This reduction can cause an increase in the wines volume or body. Lees contact is particularly effective at modifing wood tannin astringency by binding with free ellagic tannins, thus lowering the proportion of active tannins. sur lie storage can reduce the free ellagic acid by as much as 60%, while increasing the percentage of ellagic tannins bound to polysaccharides by 24% (Ribereau-Gayon et al., 2000).

Lees and color
High lees concentration can reduce color, as a function of adsorption onto the yeast cell surface.

Lees and oak bouquet
Lees modify oaky aromas, due to the ability to bind with wood-derived compounds such as vanillin, furfural and methyl-octalactones.

Lees and oxidative buffering capacity
Both lees and tannins act as reducing agents. During aging, lees release certain highly-reductive substances which limit wood-induced oxygenation. Wines have a higher oxidation-reduction potential in barrels than in tanks. Inside the barrel, this potential diminishes from the wine surface to the lees. Stirring helps to raise this potential. This is a primary reason why wines stored in high-volume tanks should not be stored on their lees. Such storage can cause the release of reductiveor sulfur-containing compounds. If there is a desire to store dry wines in tanks sur lie, it is recommended that the lees be stored in barrels for several months, then added back to the tank (Ribereau-Gayon et al., 2000).

2. Donations

The Enology-Grape Chemistry Group would like to thank the following for their support:

The Winemakers Database, Inc. has donated a comprehensive software package which integrates all aspects of winemaking from the grape to the final bottled product. This is designed to allow winemakers and research groups to better manage their production. The software is extremely flexible with powerful data base inquiry functions, automatic tracking and retroactive data collection capabilities. For additional information contact The Winemakers Database, Inc. at (707) 933-8635 or info@wmdb.com.

We would also like to thank EuroMachines for their donation which will support the expansion of our research winery. EuroMachines, a leader in wine processing equipment can be reached at their Culpepper, VA office at (540) 825-5700 or www.euromachinesusa.com.

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/. 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