By Ali Ayres

It’s decided, 2017 is the year I finally contribute to this fine festive botanical blogging tradition. But what should I write about? Holly? Ivy?  All the usual suspects have already been covered –and excellently to boot. Maybe a glass of wine would help me mull the problem over.  As I open the bottle the answer is in my hand. Cork! Whether it is a stopping the bottle of red enjoyed with Christmas dinner or shooting out of the champagne on New Year’s Eve, where would we be without it?

Merriment is all very well, but what’s the science? Cork is primarily harvested from the cork oak (Quercus suber), an evergreen oak found growing in Mediterranean-type regions in southwest Europe and northwest Africa. The cork oak can be distinguished from other oak species by its thick gnarly grey bark and it is this deeply fissured outer layer that gives us the material we recognise as cork. But why do trees produce something perfect for sealing a bottle of wine?

Anatomically speaking, cork is a tissue called phellem which forms a part of the bark and surrounds the branches of dicotyledonous plants. The cork tissue is a layer of air-filled protective dead cells which are covered with suberin, a waxy outer substance, impermeable to gases and water.  This water resistant, protective outer layer protects the tree from dehydration and extreme temperatures. Many vascular plants produce similar tissue, but on the cork oak, which needs protection against its hot, dry, fire-prone Mediterranean environment, it is particularly thick . These qualities, which enable cork to protect not just trees, but wine too, have been recognised since the the 18^th Century (Riley, 1906)

There’s no need whatsoever to feel guilty about all the wine (and consequently, people) drunk over the Christmas period, provided the wine has a proper cork in it. Cork is renewable and biodegradable. The cork oak is uniquely able to regenerate its bark meaning that cork can be harvested every 9-12 years, leaving the tree standing and causing no permanent damage (Rainforest alliance).  Save the planet. Drink more wine! (And if you recycle the bottle you’re helping even more!)

And we can thank cork for more than just Christmas merriment. Cork has given us cell theory.  In 1665 Robert Hooke observed that, at the microscopic level, cork has structures that resemble the tiny rooms, called cellulae inhabited by monks. The term ‘cell’, and subsequently a whole area of biology were born.

So think of cork as you eat, drink and be merry in this Christmas period. Or just when you wish your over-lubricated, over-opinionated relatives would put a cork in it.

References

1. Kew Science- Plants of the World online- Quercus suber L. http://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:296785-1 (Accessed: 18/12/17)

3. Species Profile: Cork Oak (Quercus suber)|Rainforest Alliance https://www.rainforest-alliance.org/species/cork-oak (Accessed: 18/12/17)
4. Cork: Biology Production and Uses- Helena Pereria. Elsevier. 2007. https://books.google.de/books?hl=en&lr=&id=5uiycUoRmFkC&oi=fnd&pg=PP2&dq=Cork+Biology+Production+and+Uses&ots=QXh8YoHpbe&sig=YROnv0THEOXTkaEysFkJ3elFIwY#v=onepage&q&f=false
5. Catry FX, Moreira F, Pausas JG, et al. Cork Oak Vulnerability to Fire: The Role of Bark Harvesting, Tree Characteristics and Abiotic Factors. Chen HYH, ed. PLoS ONE. 2012;7(6):e39810. doi:10.1371/journal.pone.0039810.
6. Riley, W. A. (1906), The History and Use of Corks and Other Stoppers. Journal of the Institute of Brewing, 12: 172–207. doi:10.1002/j.2050-0416.1906.tb02158.x http://onlinelibrary.wiley.com/doi/10.1002/j.2050-0416.1906.tb02158.x/abstract
7. Robert Hooke- http://www.ucmp.berkeley.edu/history/hooke.html (Accessed: 18/12/17)