Corks have been critical components of wine preservation for centuries, with origins dating back to the 1600s. Derived from the bark of the cork oak tree, their elasticity and impermeability has made cork the reigning king of closures. Cork oaks thrive in Mediterranean regions, with Portugal producing over half of the world’s cork. Cork is harvested by carefully removing the bark without harming the tree (every 9-12 years), allowing it to regenerate and provide cork for years to come. 

Historically, cork’s unique structure has made it ideal for sealing wine bottles, but as winemakers seek ways to overcome issues like TCA (trichloroanisole) contamination and inconsistent oxygen ingress, alternatives like technical and synthetic corks have started to give natural cork a run for its money. 

How do these types of closures differ structurally? Our Microfocus Neptune industrial CT scanner gives us comprehensive insights into the composition and density variations between natural, technical, and synthetic cork. Let’s take a look.

Natural Cork

Natural cork is an organic material composed of layers of cell walls, primarily made up of the plant biopolymers suberin and lignin, which give cork its signature flexibility and impermeability. Below in our Voyager window, you’ll find our CT scan of the cork. It shows a 2D view of the cork's Z axis, and if you move the slider at the bottom of the window from the right to the left, you can follow the path of the corkscrew.  You can toggle between 2D and 3D views by clicking the Cardinal Z ▼ button in the upper right corner of the window.

Check out the scan

The blue regions in the reconstructions represent lower-density areas, while green and yellow are medium-, and red is higher-density. The faint lines running diagonally across the cork are growth rings. We can count 9 of them, representing as many years of growth.

What about the higher-density matter? The characteristic speckled texture of cork stoppers is composed of holes called lenticels, porous structures in the cork bark that facilitate gas exchange. These openings lead to lenticular channels that are either empty or filled with loose parenchyma tissue, which allow for air movement. Surrounding these channels are higher-density cell walls (green-yellow in the scan), creating a more rigid border. This structure is critical for both the cork oak tree’s respiration and cork’s role in sealing wine bottles.

Cork is always cut perpendicular to the grain to prevent the lenticels from creating direct channels through the cork, which could allow oxygen ingress. This orientation interrupts the lenticular channels with denser cork material, ensuring the cork remains impermeable and provides a secure seal for wine bottles.

Controlled oxygen ingress through cork is beneficial for wine aging by allowing a small amount of air to interact with the wine and develop its flavors over time. However, inconsistencies in natural cork, coupled with the risk of TCA contamination (which can lead to spoiled, “corked” wine), have driven the industry to explore closure options that embrace advances in manufacturing technology.

DIAM Technical Cork

The DIAM technical cork, first introduced in the early 2000s, was developed to address TCA contamination and inconsistent oxygen ingress in natural cork. In the DIAM process, natural cork is ground into granules and then blasted with supercritical CO₂ to remove TCA and other impurities that could affect the wine’s aroma. DIAM leverages the natural strengths of cork and preserves its sensory qualities without the liabilities that have always accompanied it.

During production, the cork’s suberin—a highly elastic component—is separated from lignin, which is less elastic and discarded. The suberin is then combined with microscopic spheres (similar to those used in contact lenses), filling the voids between the cork particles and reducing porosity without increasing humidity. 

Our scan of a DIAM 5 cork (5 grade because it’s guaranteed for a minimum of 5 years) reveals a strikingly uniform structure, with an even distribution of both higher- and lower-density material that ensures reliable oxygen ingress and minimizes variability. The path of the corkscrew is clearer here, as the agglomeration process appears to have reduced the self-healing qualities of natural cork.

Check out the scan

The suberin redistribution also enhances elasticity, guaranteeing consistent performance across all corks. By removing lenticels and controlling porosity, DIAM corks provide a reliable seal without the risks of TCA or inconsistent aging, offering a solution for wines requiring both short and medium-term aging. And once DIAM establishes a track record for the long-term aging of wines, we can expect to see it used more and more.

Vinventions NOMACORC Synthetic Cork

The Vinventions NOMACORC synthetic cork, made using a patented co-extrusion process, consists of an inner foam core that controls oxygen ingress and an outer flexible skin for a tight seal. The skin even has a printed design to mimic natural cork’s growth lines and lenticels. In the scan, we clearly see the highly-porous core, and the corkscrew’s path is unmistakable.

Check out the scan

Vinventions claims the corks guarantee highly precise oxygen ingress rates, with the NOMACORC Select Green 500 that we scanned rated for 3.1 mg of oxygen after 12 months, and then 1.7 mg yearly thereafter. This control provides optimal oxygen management for wines that benefit from more exposure earlier on in their aging process. Unlike natural cork, synthetic corks are immune to TCA contamination.

Synthetic corks tend to allow more oxygen ingress compared to natural or DIAM corks, which accelerates the aging process of the wine. For wines meant to be consumed quickly, this may not be a major issue, but for those intended for long aging, the higher oxygen permeability could limit use of synthetic cork for high-end wines. 

The Verdict

When comparing these three corks with industrial CT, we see a clear distinction in their structure and performance. Natural cork, with its organic variability, provides a time-honored but imperfect seal, subject to the risks of TCA and oxygen variability. Technical corks offer a reliable, consistent solution that mitigates the risks of contamination while maintaining the characteristics of natural cork. Synthetic corks provide durability and are free from TCA, but their higher oxygen permeability makes them better suited for wines with shorter shelf lives.

In the end, the choice of cork depends on the winemaker’s goals and the intended lifespan of the wine. Natural cork remains an iconic choice for premium, long-aging wines, while technical and synthetic closures provide reliable alternatives for those looking to minimize risks and ensure consistency. With industrial X-ray CT, we can better understand a trajectory of design that began with nature and continues to this day as packaging engineers and winemakers seek to protect the quality of their wines without sacrificing the tactile charm of cork.

Learn more: CT 101