Cork Stoppers
Historical Use and growth of industry:
Cork was first used in a bottling application in the late 1600’s, when the French Benedictine monk, Dom Perignon, starting using cork to close bottles of sparkling wine. From then on, cork became and maintained the status of being the best wine stopper available, allowing a tight fit in the bottle, simple removal, and enabling the wine to breathe through the microscopic maze of cork cells and air pockets. There are between 13-15 billion cork stoppers produced every year and sold worldwide to the wine industry. The use of cork for bottle stoppers comprises almost 70% of the total value of the cork market, despite wine corks being only about 15%, by weight, of all the products produced by cork. Domestically in the US, there is continual and steady growth (approx. 7% annually) with the use of natural corks, now exceeding 900 million a year.
As for physically making the corks, the wine cork production process begins when seasoned cork bark sheets are stacked flat, and then boiled for an hour. This boiling step not only allows the 
individual cork cells to fully expand (up to a 20% increase in size) into a tight “honeycomb” cellular structure, but it also makes them flatter, smoother, more pliable. After a three-week resting period, the pressed cork planks “ripped” into strips along the length of the plank where the cork grain runs perpendicular to its length. A cylindrical knife cuts the cork to its’ proper size.
Different options/types:
Wine corks can be divided into 3 main grades: A, B, and C, and for the most part the differences relate to pore size and amount void space within the actual cork itself. The quality of wine corks varies based on its age (the age of the tree from inception, and the age since the last harvesting), and ultimately the geographic area from which it is harvested. Though there are a large number of places in the world where the cork oak grows, there is only a small swath of land, mainly in the Mediterranean, where cork of suitable quality, can be produced in suitable quantity for commercial use.
- Adapted and taken from the Cork Quality Council, a non-profit promoting education and increasing quality assurance procedures in the wine and cork industries.
Comparison to traditional products:
Other alternatives to the cork wine closures are those made of plastic and metal. In the last 10 years, approximately 20% of the bottle stopper business has gone to plastic, while 11% has gone to metal enclosure segment. This growing interest in alternatives has a lot to do with taint and avoiding it. It wasn’t until the early 1980’s that chemists were finally able to determine what caused wine spoilage, TCA (or 2-4-6 Trichloroanisole). This bacteria found in some corks can contaminate the wine by having the TCA leach into the wine.
The early plastic closures were made of solid plastic and public perception was very negative due to the difficulty in both removing and re-inserting the solid plastic. Some of the newer plastic caps are made by the combination of extruding two plastics. The softer outside and more rigid core allows a tight fit in the bottle, and easier removal out of the bottle. The main issues with the plastic closures are public perception, the fact that they provide an air tight seal when some of the nicer wines value the exchange of oxygen, and ultimately they are petroleum based.
The metal caps seem to target a certain price point wine in the North American market. In other markets like Austalia, the metal caps own the market; there is not the psychological “cheap” factor as in other countries. Though more expensive than plastic, they are easy to use and provide an air-tight seal.
Insider Knowledge:
The myth that the cork forests are in dire straits, and the reason companies are shifting to other materials due to lack of supply is false. Though a seemingly viable excuse if you decide to use other materials for bottling, there is in fact more cork in 
protection and production than there has been at any other time in recent history.
Cork producers are working at developing and employing technologies to further reduce the amount of spoilage (ie: taint) that natural corks can cause wine. This being the only main concern with wine corks, all hands are on deck to come up with a solution to control the issue even more.
Wine corks can now be recycled at “Whole Foods” stores around the country.
An interesting “specification” fact about cork stoppers: wine corks are not capable of being compressed by more than 35% of their diameter (at 24 mm diameter the cork stopper must not be compressed to a diameter of less than 15.5 mm before and during insertion).
