Enology Notes

Enology Notes #100, April 13, 2005

To: Regional Wine Producers

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

Subjects: Closure Review (continued); Upcoming Events: Wine Closure Roundtable Meeting, American Society for Enology and Viticulture, Eastern Section, Meeting; Website Postings

1. Closure Review Continued:The Wine/Enology-Grape Chemistry Group at Virginia Tech is involved in a study evaluating the impact of closures on wine volatiles. The types of closures used by the industry are as follows:

  • Natural Corks:
    Cork produced by drilling a cylinder out of cork oak, Quercus suber.
  • Colmated Corks:
    Technical corks with holes filled with synthetic compounds.
  • Technical Corks:
    Engineered cork using natural cork, but no synthetic.
  • Agglomerated Corks:
    Technical cork formed by gluing cork bits and non-cork components together.
  • 1+1 Corks:
    Agglomerated cork with two cork disks affixed, one at each end.
  • 2+2 Corks:
    Same as 1+1, except two cork disks attached.
  • Synthetic Closures:
    Any closure not made from tree bark; usually either injected or extruded polymers.
  • Screwcaps

The following are items of interest when evaluating and selecting wine closures:

  • Non-permeability
  • Elasticity/extraction force/replacement force
  • Lack of taints
  • Lack of flavor scalping
  • No crumbling/breakage/leakage
  • Desirable economics
  • Consumer acceptance
  • Tamper-evident

Wineries may begin to use specific closure products for specific wines and wine styles. Wines differ, so why not use different closures for different wines? To some extent, that is currently being done. For example, wines designed for short-term aging are more likely to be bottled with synthetics, than those that will peak in sensory quality in 7-10 years. Additionally, wines bottled with carbon dioxide to enhance the aromatic intensity are often bottled with a different closure than a product with no significant carbon dioxide.

Naturally, due to the concern about bottle variation and taints, the natural cork industry has been very proactive in steps to help minimize problems. These steps include:

  • Removal of aging cork on forest floor
  • Controlling sources of raw product
  • Not using halogens in processing
  • Boiling cork under pressure (INOS process)
  • Continuous volatile extraction of cork (CONVEX process)
  • High pressure or direct environmental load-focused inactivation (DELFIN)
  • Not reusing boiling water or cleaning water
  • Targeted mold growth (selected mold growth)
  • Microwave processing
  • Suberase treatment (phenoloxidases)
  • Supercritical CO2 extraction (Diamond method)
  • Frequent solid-phase microextraction analysis of cork lots (SPME monitoring)

There is no question that cork quality has greatly improved. However, issues such as cork variation remain. As such, both synthetic corks and screwcaps continue to receive a great deal of attention. Previous editions of Enology Notes have discussed advantages of screwcaps. Synthetic closures also offer some advantages, which include the following:

  • No dust
  • Uniform weight, size, appearance, and quality
  • Do not lose or gain moisture
  • Do not break or crumble
  • Few leakers
  • Less in-house quality control required

The degree of oxygen permeability remains a question with some synthetic closures. Additionally, it is possible for synthetic closures to have environmental taints, as discussed in a previous edition of Enology Notes.

Hogue Cellars conducted a closure study, and reported it last year. They compared natural cork, Neocork, Supreme Corq, Stelvin screwcap with Etain liners, and Stelvin screwcap with Saranex liners, using Merlot and Chardonnay. The following is a summary of their results:

  • Natural cork showed low to medium levels of taint.
  • Synthetic and screwcaps showed no taint.
  • Screwcap wines maintained fruit, were fresher (red and white), yet were less developed.
  • Synthetics showed slow oxidation, low fruit intensities, and browning.
  • Screwcaps and natural cork maintained higher free SO2 than synthetics.

More to follow.

2. Upcoming Events:

Wine Closure Roundtable Meeting. A wine closure roundtable meeting is scheduled for April 25 at Veritas Winery. The primary purpose of this meeting will be to evaluate wines bottled with screwcaps, synthetic closures, and natural cork. The background information for this meeting has been provided in Enology Notes #96 through the current issue. Wines will include products I brought back from New Zealand, and wines involved in our wine closure research trials.

There is limited seating, therefore this meeting is restricted to Virginia producers. If space is available after the deadline, registration will be opened to others.

Pre-registration will be required. Registration fee is $25; please make checks payable to Virginia Tech Foundation, and mail to Terry Rakestraw, Department of Food Science and Technology, Virginia Tech, Blacksburg, VA 24061. Please provide your email address so that we can provide registration confirmation.

If you are not a Virginia wine producer and wish to attend, do not register. Call Terry Rakestraw after April 20 to determine if space is available (540-231-6805).

Annual Meeting of the American Society for Enology and Viticulture, 2005. The 2005 annual meeting of the American Society for Enology and Viticulture, Eastern Section, will be held July 13-16 in St. Louis, Missouri, at the Millennium Hotel. This spectacular facility, on the banks of the Mississippi, is within walking distance of the Arch and downtown cultural attractions.

The meeting will involve technical presentations, the Viticulture Consortium East research summit, a wine industry trade show, the annual banquet, a local wine industry tour, and a symposium.

This year’s symposium will involve viticultural and enological discussions, and sensory evaluations, on the Cutting Edge Varieties: Norton, Pinot Gris, Traminette, and the cold-hardy Frontenac and La Crescent. Speakers from the academic community, commercial growers, and winemakers will present practical information and extensive sensory evaluations. For information and registration, see the website at http://www.nysaes.cornell.edu/fst/asev/.

3. Website Postings. An overview of Brettanomyces, and a portion of the Wine/Enology – Grape Chemistry Group’s Winery Planning and Design manual will soon be posted on our website, at http://www.vtwines.info/.

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/.

To be added to (or removed from) the Enology Notes listserve send an email message to with the word "ADD" or "REMOVE" in the subject line.

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