What you need to know about cork stoppers
What is cork, and why is it used to seal wine bottles?
Cork is, essentially, 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 coat the walls of the cork cells, preventing the passage of water and gases. Suberin is practically infusible and insoluble in water, alcohol, ether, chloroform, concentrated sulfuric acid, hydrochloric acid, etc. And not only that, but since about 60% of cork is composed of gaseous elements, this material is extraordinarily lightweight.
These tiny "air cushions" allow cork to compress to about half its thickness without losing flexibility, regaining its original shape and volume as soon as the pressure is released—a characteristic that is very useful 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 making cork stoppers, although very meticulous, is fairly easy to follow. It all begins with harvesting the cork. Contrary to some misconceptions, this process does not require cutting down any trees; in fact, cork oaks are a legally protected species, and as such, it is illegal to cut them down unless they have already died (and even in that case, written permission from the authorities is required).
During harvesting, the outer bark of the cork oak (what we know as cork) is carefully stripped from the tree trunk so as not to damage it. If you’re curious to learn more about how harvesting is carried out, read our article on the subject. Once the cork has been harvested, it is left to rest before it can be industrially processed. Next, the cork is treated to remove impurities that could affect its performance as a sealing material. If you’d like to learn more about the manufacturing process for natural and technical cork stoppers, visit our page on the subject.
What are the different types of cork stoppers?
Cork stoppers come in different types, shapes, and sizes, depending on their intended use: still wines, sparkling wines, liqueurs, etc. The most common and highly regarded type is natural cork, which consists of cylindrical shapes cut directly from a cork slab. Natural cork is the most traditional type of cork stopper and also the most sustainable, since it uses no raw materials other than cork, which is biodegradable and renewable. Natural cork stoppers also offer some unique advantages for aging, 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, as the slabs must meet specific requirements to be used for this purpose. And not only that, but during the drilling of natural cork stoppers, some pieces of cork slab are left over. To allow these leftover pieces of cork to be reintroduced into the production process, they are ground up and used to manufacture technical cork stoppers. Technical cork stoppers are made from natural cork granules mixed with a food-grade binding agent, which gives them their consistency. Technical cork stoppers are ideal for wines meant for immediate consumption, as they do not offer the same aging benefits as natural cork stoppers but provide excellent value for the price.
In addition, since technical cork stoppers can be molded into any required shape and can be made denser than natural cork, they allow for the production of cork stoppers for sparkling wines, which are larger than those for still wines and must withstand higher pressure. You can find more information about the different types of cork stoppers on our products page.