Enology Notes

ENOLOGY NOTES #8 November 9, 2000

To: Virginia Vintners and Prospective Vintners

From: Bruce Zoecklein

Subjects: A viticulture HACCP plan , Wine structural development, Web site

Viticulture HACCP plan. As recommended in editions of the Vintner's Corner newsjournal, each producer should determine when, why and how wines should be evaluated by chemical, microbiological and sensory analysis. The establishment of a HACCP (hazard analysis and critical control points) plan allows for that determination.

During the early rainy portion of this harvest season, I received several inquiries from reporters asking about spray materials used in Virginia vineyards. The perception was that we use a lot and that arid California uses few. While this is not the case, it is yet another reason to establish and implement a viticulture HACCP plan. Many buy fruit from independent growers. Do you know that the person responsible for spraying has been properly trained and certified? Do you have a written certification that only approved chemicals were applied to the fruit you purchased? And that the proper spray- to-harvest interval was followed? Protect yourself and

our industry by establishing a formal program for next season!

Managing structural development. Proper management of structural development allows red wines to properly age while limiting the risk assertive dry tannins.

The availability of high quality grape-based tannins has been a significant enological advancement. Grape tannin formulations, used pre-fermentation (and occasionally soon after fermentation) can contribute both structure and color stability by influencing the anthocyanin/tannin ratio.

Today's enological tannins are generally made from white grapes. They differ in purity, portion of the fruit extracted (skin vs seed tannins) and the extent to which the tannins are in the native or un-reacted form (degree of oxidation and polymerization).

The relative proportion of seed to skin-based tannins varies with the product. Seed tannins contain large molecules which react quickly with oxygen. Therefore, seed tannins evolve or 'mature' quickly with oxygen exposure. Skin tannins, on the other hand, contain a high percentage of polymerized tannins and require a greater amount of oxygen.

Thus, red wine oxygen management for structural enhancement should be a function of the nature of the commercial tannins added, if any, and production methodology . For example, wines produced by Delestage (usually low relative seed tannin concentration) should not have the same oxygen exposure as those produced by conventional fermentation.

As our ability to separate tannin fractions increases, commercial tannin preparations will become an increasingly important production and stylistic tool. Wines were produced from a variety of tannin products this season and will be reviewed at upcoming Winemaker Roundtables and/or extension meeting.

Our web site. The web address for the Enology-Grape Chemistry Group is www.fst.vt.edu/zoecklein/index.html. The address has newjournals, short course notices, research activities etc. We have had some problems with our server. If you have any difficulties accessing this address, please let me know-you can assist us by communicating any access problems.