The season of feasting and drinking merrily is upon us, and it’s time to polish your corkscrew, because cork is making a comeback. While screw-top lids have dominated the Australian and New Zealand wine scenes in recent decades, a new generation of local vintners is reviving the centuries-old practice of using corks to seal wine bottles in the name of sustainability.
So, as you pop open a bottle of bubbly or reach for a top-shelf tipple to celebrate the festive season, let’s consider the origins and environmental impact of cork.
How is cork harvested?
Cork is harvested exclusively from cork oak trees that are endemic to the Mediterranean, with Portugal leading global production, followed by Spain, Morocco and Algeria. Rather than felling these trees to extract the material, cork oaks are left standing for generations while skilled harvesters peel long planks from the trunk by hand.
Cork cutters must maintain expert precision so the tree isn’t damaged, and can regrow this lost layer ready for harvesting again in another nine years. Cork oaks can stand and continue this cycle for more than 200 years, meaning they see around 20 harvests in their lifetimes.
Once harvested, the bark is left outside to ‘cure’ for at least six months, where the moisture content stabilises through ventilation and drying. It’s then boiled, trimmed and cut into natural wine corks, with lower-grade bark being ground and re-agglomerated for other products used across construction and manufacturing industries.
Is cork a ‘carbon sink’?
Because cork oaks stand for centuries, continuously growing and repairing their bark post-harvest, they do a fantastic job of absorbing carbon dioxide through photosynthesis. Like all flora, this process locks CO2 away in plants’ roots and branches.
Thanks to the harvest cycle, these hardy trees use more CO2 than average so their carbon storage capacity keeps increasing during their long lifespan. Plus, no organic debris is left behind post-harvest to decompose and release CO2 back into the atmosphere like you’d see with traditional logging.
This means the harvesting of cork helps remove more CO2 from the atmosphere than it creates, making it a carbon negative process or a ‘carbon sink’.
Cork wine stoppers vs screw-top caps
About 2-3% of wine topped with a cork develops a musty flavour, creating an affect known as ‘corked’ wine. Depending on the sensitivity of your palate, discerning wine drinkers may be able to detect if a wine is corked based on smell or taste. The odour or flavour is the result of fungi growing in tiny air pockets within the cork and producing a chemical called trichloroanisole. It’s harmless, but can contaminate wine in the bottle and affect flavour if it accumulates.
While the risk is low, corking is the reason many modern winemakers turned to screw-on caps. The problem is that these caps are often made from mixed materials (usually an aluminium base with a plastic or tin coating) from virgin sources, making them a less sustainable option than their cork predecessors.
In recent years, cork producers have begun using supercritical CO2 technology to clean corks of contamination (the same method used for decaffeination and to extract nicotine from tobacco). As a result, cork-topped wines are enjoying a revival.
Bottling a fine shiraz is certainly not the only use for cork. Being lightweight, durable, elastic, compressible and fire-resistant, cork is ideal for tasks in the construction industry like thermal or acoustic insulation. You’ll see it pop up in flooring, shoes, artificial sports turf, sporting equipment and even concrete bridges to aid with shock-absorption and expansion in joints.
How to recycle cork
Used cork can be granulated and repurposed in many of the new products listed above, and also as mulch in the garden or pot plants. Cork dust produced in the manufacturing process can even be burned as an alternative to fossil fuels to power production efforts.
If you’re looking to recycle cork wine stoppers over the holidays, check out TerraCycle’s Cork Zero Waste Box. You can recycle both natural and synthetic corks with this pre-paid solution. Consider teaming up with family or neighbours to purchase a box if you want to spread the cost and the sustainable love this festive season.
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