Enology Notes #47, June 4, 2002
To: Virginia Vintners
From: Bruce Zoecklein
Subject: Winemakers Roundtable Meeting June 24 (Sensory Evaluation of Reds, VQA and Remission Phtometry), New Web Site Domain Address, Fining Continued-PVPP
I will conduct a Winemakers Roundtable meeting Monday, June 24, 2002 from 1:00 pm to 4:00 at Horton Cellars.
This meeting is for commercial Virginia wine producers only. Please bring one bottle of unfinished red wine to share with the group.
In addition to wine evaluation, we will have a brief discussion on the establishment of a Virginia VQA (Vintners Quality Alliance) system. I have previously outlined the basis of the system used in Canada (see Enology Notes number 40, posted on the web).
At the Winemaker Roundtable, if time permits, I will demonstrate the use of Remission Photometry and discuss its viability as an analytical tool for our industry.
We have added a new address that will allow access to the Enology-Grape Chemistry web site. Use the old address or the new domain: http://www.vtwines.info/
In previous editions the importance of wine structure/texture balance has been discussed. This balance is the result of the interaction of volume or body, acidity, roughness, tannin intensity, astringency, dryness and bitterness. As discussed, these palate features can be influenced by fining agents.
Polyvinylpolypyrolidone (PVPP) is a synthetic, high-molecular-weight fining agent composed of cross-linked monomers of polyvinylpyrolidone (PVP). PVPP is a "proteinlike" fining agent with affinity for low-molecular-weight phenolics. The mechanism of action is hydrogen bond formation between carbonyl groups on the polyamide (PVPP) and the phenolic hydrogens. As a selective phenol absorbent, PVPP is available in several particle sizes. Unlike the soluble protein fining agents that remove larger polyphenols by conforming with the molecule, insoluble PVPP contacts relatively few reactive groups. Therefore, PVPP finds its major application in binding with and removing smaller phenolics such as catechins and anthocyanins, which conform to the PVPP molecule. These compounds are precursors to browning in white wines, and browning and bitterness in red.
PVPP may be effective in "toning down" bitterness or the potential for this problem in wines. PVPP is most beneficial immediately post-fermentation, but is occasionally added to juice and removed by settling before fermentation. PVPP treatment of Traminer must reduces the formation of 4-vinylguaiacol, an important character impact compound for the variety. It may be a benefit in prefermentation fining of juice from moldy grapes and for removing excess color for blush wine production. PVPP removes more tannin and anthocyanin than gelatin. This represents a potential problem in use of this agent in red wine fining. In addition, PVPP is used in removal of browning or pinking precursors in young white wines. Recommended use levels are from 12 to 72 g/hL (1-6 lb/1,000 gal). PVPP has the ability to strip wine complexity. It is therefore desirable to fine juice or young wines before the development of aged bouquet.
Subscription to Enology Notes. All past Enology Notes and Vintner's Corner newsjournals are posted on the Enology-Grape Chemistry Group's web site at: http://www.fst.vt.edu/zoecklein/index.html.
Enology Notes are slightly different in content from this subscription based Vintner's Corner newsjoural. To be added to the Enology Notes list serve send an email message to bzoeckle@vt.edu with the word "ADD" or "REMOVE" in the subject line.
Dr. Bruce Zoecklein
Associate 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: www.fst.vt.edu/zoecklein/index.html
Phone: (540) 231-5325
Fax: (540) 231-9293
Email: bzoeckle@vt.edu