More to Cork Than Meets the Bottle

Any way that you pull it - with a corkscrew, wine puller, or some other modern contraption designed to remove it from a bottle - a wine cork has a history of its own. That history begins in about 500 BC in Greece where cork was reportedly used as a stopper for wine jugs. Prior to that, olive oil was floated over the top of wine in ancient Egypt, and it was a practice that was still common throughout the ancient world until the Middle Ages.
As cork caught on, Portugal with its large population of cork trees (which are a type of oak) became the focus for a whole industry that has supported the wine industry. The cork producers take processing cork to be ready for a wine bottle just as seriously as a winemaker takes in turning grapes into a fine wine. More importantly, it takes more time to produce a cork than it does a wine.

The typical cork tree takes about twenty-five years to mature and then it must undergo a couple harvests of its outer bark before it is ready to be used as cork for wine bottles. Those early harvests do not provide material dense enough for stopping a wine bottle, so most of the producers have other materials such as cork tiles for floors and walls that are byproducts of that process. Some wineries in Portugal even use cork as their wine labels, because it can be easily branded with the name of a winery.

Each of the cork harvests need a 7-9 year waiting period before the cork can be harvested again. Once the bark is harvested off the cork trees, they look like they have undergone the ultimate body peel. After the cork manufacturers have aged, washed, and sterilized the cork, it is then punched into the shape it will have for insertion into a bottle. However, that is only part of the process. Bags of cork are then shipped to the United States for further processing.

In visiting Cork Associates in Napa, a production arm of the largest cork producer in Portugal, we found that the process still had many more steps before a cork was ready to be sent to a winery for its journey to fulfill its purpose of preserving a wine. Here, the corks were graded for quality. If they have defects, look too coarse, or have some other problem, they will be removed before they go any further. Wineries buy corks based on their quality, and prices are determined by premium quality. Corks are then washed, usually with hydrogen peroxide, although chlorine was widely used in the past, to disinfect them of any impurities. The cork producers even do lab tests to check the quality throughout the process.

Following their journey through quality control, the corks are de-dusted. This makes the corks ready for printing or branding with a winery’s name or logo. In some cases, a winery will use both forms of marking their corks; it’s a flashy way to remind the consumer about who produced the wine. An ozone-treated humidity room is where the corks stop next to make certain they are at the optimum pliability.

The next step is coating the corks with emulsified paraffin or silicon to create a good seal so the cork will be uniform against the glass. Then, they are tumbled in large industrial dryers that look like they belong in a laundromat. Finally, they are given a small dose (35 parts per million) of sulfur dioxide to prevent any contamination on their way to wineries or while they are being stored. Plus, the corks must be between 5 1/2 to 7% humidity in order to work effectively.

What happens if corks are not treated properly or become too moist? One result can be the development of mold that will lead to a wine being "corked." While every step of the process takes every precaution to eliminate this problem, industry experts estimate that between 5-8% of all wines have the musty dusty odor often associated with it. Fortunately, the majority of wines are preserved as they are meant to be.

All of us are looking for a little "closure" in our lives, and in the case of a bottle of wine, cork has been the answer. However, with the supply of cork trees diminishing at a fair rate of speed, the cork is being challenged by other adversaries wanting to be the next on the bottling line. The introduction of synthetic corks, as the ultimate method of sealing out oxygen from the bottle, has many wine purists up in arms.

The cork industry not wanting to waste any byproducts has taken to shredding leftover cork pieces and then gluing them back together to make a "composite" cork. Then there is always a screwcap, but where is the romance in that? The incredible journey cork takes from tree to bottle is an important part of the winemaking quality. It plays a significant role in the preservation of the investment wineries make as they produce super premium wines for consumers.

Most importantly, the process of cork production is paramount to producing good wines. Without it, how could you set the mood of removing the foil, inserting the corkscrew, hearing the pop of the cork, watching the bottle’s contents glide into the glass, and then tasting the wine as it caresses your palate.

Tim Hayes & John Koetzner
Wine Tributaries