Cork stoppers: what you need to know
What is cork, and why is it used to seal wine?
Cork is the outer bark of the cork oak. It is a 100% natural plant tissue composed of numerous microscopic cells filled with a gas identical to air. The cells are primarily coated with suberin and lignin. The main component, suberin, is a mixture of organic acids that coats the walls of the cork cells, preventing the passage of water and gases. Suberin is practically infusible and is insoluble in water, alcohol, ether, chloroform, concentrated sulfuric acid, hydrochloric acid, etc. Furthermore, since about 60% of cork is composed of gaseous elements, this material is extraordinarily lightweight.
These tiny "air pockets" allow cork to be compressed to about half its thickness without losing any flexibility, and it regains its original shape and volume as soon as the pressure is released—a very useful characteristic for sealing wine. At the same time, suberin makes the walls of the cork cells impermeable and, therefore, airtight. Cork’s unique properties make it ideal for a variety of applications, which no other technology has been able to replicate or surpass.
How are cork stoppers made?
The process of manufacturing cork stoppers, while very meticulous, is quite simple. It all begins with the harvesting of cork. Contrary to some misconceptions, this process does not require the felling of any trees—in fact, cork oak trees are a legally protected species, and as such, it is illegal to cut them down unless they have already died (and even then, written authorization from the authorities is required).
During harvesting, the outer bark of the cork oak (cork) is carefully separated from the tree trunk so as not to damage the tree. If you’re curious to learn more about how cork is harvested, read our article on the subject. Once harvested, the cork is left to rest before it can be processed industrially. Next, the cork is treated to remove impurities that could affect its performance as a sealant. To learn more about the manufacturing process for natural and technical cork stoppers, click here.
What are the different types of cork stoppers?
Cork stoppers come in various types, shapes, and sizes, depending on their intended use: still wines, sparkling wines, liqueurs, etc. The most common—and most highly regarded—type is natural cork, which consists of cylindrical shapes cut directly from a cork plank. The natural cork stopper is the most traditional type and also the most sustainable, as it uses no raw materials other than cork—which is biodegradable and renewable. Natural cork stoppers also offer some unique aging benefits, as some of the oxygen “trapped” in the cork’s cellular structure interacts with the wine, allowing it to reach its full potential.
However, not all cork is suitable for natural cork stoppers, since the slabs must meet specific requirements to be used for this purpose. In addition, during the drilling of natural cork stoppers, some pieces of cork slab are left out. To allow these discarded pieces of cork to be reintroduced into the production process, they are ground up and used in the manufacture of technical corks. Technical corks are made from natural cork granules mixed with a food-grade binding agent, which gives them their consistency. Technical corks are ideal for wines meant for immediate consumption, as they do not offer the same aging benefits as natural corks but provide excellent value for the price.
In addition, since engineered corks can be molded into any shape required and can be made denser than natural cork, they allow for the production of corks for sparkling wines, which are larger than those for still wines and must withstand greater pressure. You can learn more about the different types of corks on our products page.