Wine bottle closures have one main purpose: to preserve the integrity of the product until the bottle is served. Since the time of Dom Pérignon (circa 1668), cork has been the primary wine bottle closure. Its light weight, elasticity, near impermeability to liquids and gases, lack of flavor impartation, long life span and wide availability have endeared it to the industry and consumers.
In the last 20 years the love affair with cork has taken somewhat of a turn. Its enhanced ability to seal bottles from oxidation through expansion due to its porosity also makes it a potential carrier of wine taint, in particular 2,4,6-trichloroanisole (TCA).
TCA-contaminated wine, commonly described as “corked,” is musty and unpleasant, both in aroma and taste. TCA in very low levels can also be relatively imperceptible, but reduces aroma and increases astringency in the wine.
While TCA can come from contaminated corks, it has also been found in barrels, winery and bottling equipment and airborne molds. Other sources are wood pallets and structures, resins, plastics, paper, wood preservatives, fungicides, filter pads, fining agents and sanitizers that are chlorine-based.
Yet, TCA contamination motivated many wine producers to seek other, less permeable, alternatives to cork. With modern science, it seems antiquated that closures from tree bark with their potential to destroy product integrity are still used.
Due to the great potential for cork to hold TCA and the possibility for it to quickly pick up taint, the search for alternative closures has been very aggressive. While the actual percentage of tainted bottles is believed to be significantly lower than the reported 5-10 percent, even 2 percent spoilage for a 60,000 case winery equals the disturbing impact on 1,200 cases.
There are a variety of designs of plastic corks in the market. They were developed to increase consumer acceptance of alternative closures because they strongly resemble natural cork. But there are trade-offs: While consistent in size, plastic corks don’t always conform to bottlenecks that are larger than specification. They can be challenging to remove (both from the bottle and the corkscrew), and they allow greater oxygen passage than natural cork.
Consumers have been slow to accept screw caps despite their effectiveness. Screw caps seal wine with less potential for oxidation than natural corks, and long-term experiments have shown them to be effective over many years, though producers may only guarantee them for the short term. The drawbacks for screw caps are their image and their tight seal, which creates an environment for reduction, a natural process by which – in the absence of oxygen – aroma and flavor can become withdrawn. This can be counteracted by aeration after opening.
The Vino-Lok or Vino Seal, is a promising, resealable glass stopper with a seal of ethylene-vinyl acetate. Invented in Germany in 2004 by Alcoa, it keeps the wine fresh and prevents oxidation as effectively as screw caps, but also encourages reduction. It needs a capsule to help guard against tampering.
Even with TCA challenges, cork still offers exceptional characteristics as a closure.
Cork producers realized their production and testing processes needed to be adapted to reduce TCA, and progress has been made. Water baths are tested between lots of corks to ensure taint is not passed to following batches. Steam (ROSA, or Rate of Optimal Steam Application, a proprietary process), carbon dioxide and peroxide processes have been developed for TCA removal. All of these steps have resulted in a dramatic reduction of taint.
There are Portocork’s “Neutrocorks,” where granules of cork have TCA removed before being formed into a straight agglomerate cork. Twin Top cork has a center of agglomerate cork with fine cork discs placed at either end. Such innovations have been successful in fighting TCA wine infection.
While alternative closures have benefited from much experimentation and new developments, cork is still a vital and important wine bottle closure. The future will see further evolution in quality control in natural cork and new alternatives to ensure that the product put into bottle will be what the consumer enjoys on opening.
- Recent studies in Bordeaux have shown that cork does let some air into the bottle, which impacts the aging and evolution of wine.
- The potential lifespan of top quality cork is 25 years.
- There is enough cork in the Portuguese forests to last for the next 100 years. Cork forests are also being expanded with reforestation by 4 percent a year.
- Sixty percent of bottles are still sealed with cork.
- Ability to detect cork taint varies by individual, though some can detect it at a level of single-digit parts per trillion. Six parts per million is 6 inches in 16.85 miles. Per trillion would be this figure times 100,000. TCA is a very potent taint.
- TCA is our most common and persistent food-grade taint, found in packaged foods, clothing, bottled beer (permeates the plastic crown cap seal) and bottled water (permeates the plastic bottle). It is not known to pose any health threats to consumers.