A winery evaluates synthetic cork

Wines & Vines, July, 1992

The St. Francis Winery in Sonoma Valley has just released 2,700 cases of its most popular vintages with one unusual twist: the bottles are sealed with a new synthetic cork said to overcome both the performance problems of natural cork, and the image problem of screw caps.

Called Cellukork|TM~, the new stopper maintains the look, feel, and traditional appeal of natural cork while eliminating the problems associated with cork that currently undermine the finest efforts of enologists worldwide.

After 10 years of development and testing by Lermer Packaging Corp., full-scale production of Cellukork is now underway in Ontario, Calif. In the last several months, over 300 wineries in the U.S., France, Italy, and Africa have begun testing the new closure, with St. Francis one of the first to evaluate, approve, and release it commercially.

Problems inherent with natural cork

The problems that arise when bottling wine with natural wood-bark cork have plagued winemakers for centuries, and many believe the situation is worsening. The accepted industry figure is that 0.5 to 6% of wine is spoiled by cork tainting.

"In the last 4 or 5 years I have noticed more spoilage and more tainting contributed by corks than in the past," says Thomas J. Mackey, winemaker at St. Francis. He estimates that between 3 and 7% of all wine today is affected by cork taint, and attributes this increase in part, to a decline in cork quality.

"The demand for cork is increasing, and this puts a lot of pressure on the cork suppliers to take the cork bark off the trees possibly before they should, so there probably is some lesser quality cork getting through."

Natural cork is not inert and contains volatile compounds, a number of which can be passed on to the wine, altering its taste. Mold and other microorganisms growing on the cork's surface and interior can impart a musty, moldy aroma and flavor defects.

Chlorine used to bleach cork can react with mold, forming substances such as 2, 4, 6-trichloroanisole (TCA). TCA gives off an intense odor, affecting the wine's aroma even when present in ratios as low as one part per trillion. Even cork that is correctly treated with chemicals and/or boiled, can become recontaminated prior to bottling by airborne microbes.

"If consumers pull the cork, taste your wine, and find it is flawed, they are likely to attribute it to poor quality wine rather than a bad cork, and they probably won't buy that vintage again," notes Mackey.

Jean-Michel Riboulet, director of the Center for Improvement of Quality in Enology states "cork stopper taste is more likely to be detected today than in the past." He attributes this to improved winemaking -- which produces cleaner, more technically correct wines with fewer abnormal tastes and aromas -- coupled with an increase in the average consumer's knowledge.

"Because of cork problems, what I have done in the past two to three years is buy from quite a few different suppliers to 'hedge my bets,'" says Mackey. "If I run across a bad batch, at least it will be a smaller percentage of the run."

He has also implemented a "fairly rigorous" cork quality control program involving a variety of quality checks -- including visual inspections, soak tests, moisture checks, and dimensional checks -- on approximately one percent of his cork inventory.

Screw caps solved one problem, but created another

To create a leakproof, taint-free, low-cost seal, screw caps are ideal, but they suffer an image problem that is reinforced by wineries that typically employ them only for their lower-end products.

T.H. Lee and R.F. Simpson of the Australian Wine Institute state it simply: "The consumer continues to associate a cork with quality wine" . . . and a screw cap with "cheap" wine. Adds wine writer Dan Berger: "wine connoisseurs love the ritualistic removal of the cork."

The synthetic cork alternative

Difficulties with natural cork and cork suppliers prompted Mackey to investigate Cellukork.

The cork substitute is injection-molded from ethylene vinyl acetate. Inert gas, generated during the molding process, creates the small interior voids that give the synthetic material compressibility, elastic recoil, adherence, and other physical properties similar to that of wood bark cork.

Because the acetate polymer formulation is inert, it has no affect on wine flavor or aroma.

Whereas natural cork is often treated with chemicals to remove dust and disinfect the wood, Cellukork requires no washing or processing of any kind prior to insertion.

These characteristics, coupled with Mackey's frustration with natural cork, prompted him to give Cellukork a try. His initial trial was to bottle six cases of '89 Merlot with the new closure and conduct tests monthly to evaluate its performance.

"I've been trying these bottles, and the results are quite promising. As far as contribution to taste, none has been detected in double-blind taste tests. The only difference was that the Merlot sealed with Cellukork tasted a little bit fresher than that bottled with traditional cork . . . the fruity character was more prominent."