Cork Research

Review the most recent research on cork taint issues, oxygen issues, and sensory issues, along with industry surveys.

Cork Taint Issues

Screening Cork Shipments
with Group Soaks

A Successful Application of Chemical Cork Screening Methods Presented by Gordon Burns ETS Laboratories - Wines & Vines Packaging Conference - August 2015 - Napa CA

  • This presentation reviews the successful application of group cork soaks and chemical analysis as a screening tool to detect TCA in cork shipments prior to processing. The presentation displays data from several bottling experiments that compare TCA in bottled wine to the “releasable TCA” detected in prior group cork soaks. Results show that group cork soaks within the range of acceptability by the CQC effectively eliminate cork populations that would pose a problem in bottled wine. The researchers identified a “threshold” effect that indicated releasable TCA needed to be at least ̴4ppt for TCA to reach 0.5ppt in bottled wine.

Consumer Sensory Detection of TCA in Wine

Estimating a ‘‘consumer rejection threshold’’ for cork taint in white wine -
John Prescott, Leslie Norris, Madeleine Kunst, Sandra Kim - "Food Quality and Preference"

  • Two consumer studies - one triangle test was designed to identify the detection level of TCA in white wine (2.1ppt) - the second was a sequential test designed to identifiy what concentration of TCA caused consumers to prefer the control over the spiked sample (3.1ppt).

NCC Study of Disk Performance in Preventing TCA Transfer from 1+1 Corks

Study of the transfer of TCA to bottled wine with various components used in the manufacture of technical corks - February 2010

  • Results of a 24-month study of wines bottled with technical corks made with components selected for either high or low TCA concentration. Final results showed that disks with low TCA concentration successfully inhibited TCA migration from agglomerated bodies selected for high TCA concentration.

NCC Study of Chemical Origins for Off-Aromas in Wine

Analysis of rejected wines at Sonoma County Harvest Fair Presented by Peter Weber NCC - ASEV Eastern Meeting - June 2003 - Lancaster PA

  • Study compared 40 wines rejected by judges for off-aromas to the accepted control sample. Eight compounds commonly associated with cork defects were analyzed. Only TCA showed correlation to sensory rejection. The other seven compounds were either not measurable, or found in equal frequency between the rejected wines and the acceptable controls.

American Vineyard Foundation Study of Group Soaks as a TCA Screening Tool

Screening natural corks by their releasable TCA : Does it Work? Presented by Eric Herve PhD, ETS Laboratories - Sponsored by the AVF - APCOR Cork Seminar - June 2006 - St. Helena CA

  • Demonstrated that group cork soaks accurately portray the average of the individual corks. Further showed that these average scores can are closely related to TCA concentration in bottled wines. Summarizes that group cork soaks are a valid QC tool. Illustrates that low TCA Bales produced very small percentages of cork taint in bottled wine.

ETS/NCC Study of Releasable TCA and its Behavior in Bottled Wine

The original study of the interaction between cork, wine and TCA.  Presented by ETS/NCC at the ASEV Annual Meeting - July 1999 - Reno NV

  • Report of the development of GC/MS SPME analysis of TCA in cork soaks. This study established the correlation between TCA observed in group cork soaks with transmission of TCA to bottled wine. The work introduced the term "Releasable TCA" and has proved to be the foundation of quality control programs throughout the world's cork industry.

Oxygen Issues

Do Cork Closures Protect Wines from Dimethyl Sulfide Aromas?

WIne Business Monthly - June 2011, Published NCC survey - April 2011

  • Review of literature describing the behavior of Dimethyl sulfide (DMS) in bottled wines. Outlines storage conditions that cause DMS to develop including temperature and the effect of low permeation closures .Includes two market surveys of commercial wines by closure measuring observed DMS by closure type. Concludes that the use of cork closures may reduce the effect of DMS.

AWRI Closure Comparison at 18 Months

Excerpts from the AWRI Closure Report as seen in Australian Journal of Grape and Wine Research 7.64-05.2001

  • This presentation is a summary of data presented in graphical form from the oft-quoted AWRI Report on Wine Closures. Much of the data has been selectively reported by various manufacturers of alternative closures. In this display, all of the sensory results are reported together. At the 18-month point there appear to be several conclusions:

    • No single closure demonstrated completely satisfactory results.

    • Synthetic closures had significant issues related to off–aromas and oxidation.

    • Screwcaps had better results regarding oxidation but showed evidence of “glue–like” and “reduced” off–aromas.

    • Natural Cork had good marks regarding fruit retention and oxidation. Off–aroma issues were primarily related to TCA.

Characteristics of Oxygen Permeability in Wine Closures

Presented by Paulo Lopes PhD, University of Bordeaux - APCOR Cork Seminar - June 2006 - St. Helena CA

  • This study incorporates a colorimetric method for detecting oxidation, allowing more precise measurements of oxygen ingress than most previous work. Dr. Lopes demonstrates the comparative differences between wine closures in allowing oxygen ingress. His findings conclude that (1) Synthetics were too permeable – and caused premature aging (2) Screwcaps were not permeable enough – and did not allow proper aging. The implication was that natural cork offered a perfect balance.

Post Bottling Reduction and Permeability Performance

Presented by Alan Limmer PhD, Stonecroft Winery NZ - APCOR Cork Seminar - June 2006 - St. Helena CA

  • Dr. Limmer’s experience as a New Zealand winemaker gives him extensive familiarity with modern screwcap closures. His presentation explains the source of reduced aromas that can be encountered when a lack of oxygen is present in wine. Dr. Limmer is convinced that many wines suffer loss of fruit and present a characteristic "dullness" when this condition occurs.

Sensory Issues

Sensory Detection and Recognition of TCA in Various Matrices

Sponsored by the NCC and Conducted by ETS Laboratories in July 2001 - St. Helena CA

  • A total group of 33 winemakers and enologists were presented with a rang of wine and cork soak samples spiked with TCA in a range from 1ppt to 32ppt. Results showed a wide range of sensory effectiveness. Overall average TCA recognition occurred at approximately 6ppt, with no major differences between wine types or cork soaks. False positives were approximately 35% for samples spiked at levels of 4ppt or higher.

AWRI Commercial Closure Trial

  • Flavor Characteristics — A recent closure trial conducted by AWRI supports the observation of many winemakers that cork finished wines compare favorably to alternatives in flavor complexity, development and balance. In this example, sponsored by the developer of a new coating polymer, bottled samples of wine finished under corks, screwcaps and synthetics were evaluated after 24 months of bottle age.

    Results show the two cork-based products had superior expressions of fruit and “developed” flavors than the same wine bottled with alternative closures.

    In this study, the samples finished under screwcap had significantly higher negative components than did the cork or synthetic closures.

Flaws Responsible for Commercial Rejection of Wines

Sponsored by APCOR and conducted by ETS Laboratories - Presented by Tracy Dutton, Culinary Institute of America and Eric Herve PhD, ETS Laboratories - APCOR Cork Seminar - June 2006 - St. Helena CA

  • WInes rejected at the Culinary Institutes restaurant and classrooms were analyzed for a wide range of faults. Most noteworthy, out of more than 4,500 wine opened during the test period - only 10 wines were rejected. Of these flawed wines, nearly all showed a combination of high TCA levels and oxidation issues. Imported wines were more likely to be rejected than domestic products.

Behavior of TCA in Wines with Higher Alcohol

Sponsored by NCC and conducted by ETS Laboratories - Eric Herve PhD, ETS Laboratories - June 1999 - St. Helena CA

  • Alcohol has a high affinity for TCA and there have been understandable questions about the CQC method which specifies a standard 10% ethanol solution for cork soaks. This report illustrates that higher ethanol matrices will absorb more Releasable TCA from the cork, but at the same time, will curtail the volatility of TCA into the atmosphere. The net effect is shown in this study, to cancel each other out. It is inferred from this analysis of reduced TCA release to a SPME fiber, that the same result would occur in sensory evaluations.

Industry & Consumer Surveys

Consumer Attitudes towards Wine Closures

Tragon Corporation - 10/2011

  • An update of research originally performed in 2004, this study tracks consumer attitudes towards favorability of different closure types, perceptions of quality and the appropriateness of use for different occasions.

Consumer Preferences for Natural Corks

Sponsored by Amorim Cork America, Cork Supply USA, Portocork America and a leading North American winery

  • This focus group survey was designed to identify the most desirable qualities of natural cork. Overall results indicate that consumers consider natural cork to be a welcome tradition that assists the proper aging of wine. Respondents considered "ease of extraction" to be the most important physical characteristic of a good cork

Closure Survey of Sommeliers

Sponsored by APCOR - Presented by Balzac Communications, 2006

  • Paul Wagner reported the details of his survey of wine educators and sommeliers. Highlights were that these trade figures believe that the vast majority of consumers preferred natural cork to alternatives.

Survey of Storage Practices for California Wineries

Sponsored by NCC - Feb, 2007

  • The CQC conducted an informal internet survey to 100 responding wineries concerning storage conditions for their wine. Respondents were asked to estimate the aging time of their wine from release to final consumption. Wineries were also asked to describe the bottle orientation of their wines in storage and in shipping.