Newsletter March 2021
Cork’s Biggest Mystery - Solved?
“Oxygen makes the wine, which ages under its influence.”
Louis Pasteur, 1873
Cork is known to breathe (Oxygen Transfer Rate or OTR) and its influence on making beautiful wines is well known but nobody has ever known how it breathes.
Looking at cork density, cracks, defects and growth rings has never provided a strong correlation to the right amount of breathing that wine requires. As a result, the most common cork problems, after the ever present and highly variable cork tannin, are too much breathing and too little breathing; the latter also known as a reduction fault.
WHY can two perfect looking corks cut from the same piece of bark have dramatically different oxygen transfer rates?
Cork was the first material ever observed under a microscope. When Hooke in 1665 published his drawings of the first cells ever seen, the world was amazed, his fame was cemented and his term “cells” is now used everyday around the world. However, under the light microscope there was no path seen (and one has never been seen) for air to flow through the cork and yet it obviously does.
The answer as to why two perfect looking corks can have a dramatically different oxygen transfer rate is in the variable number and size of tiny communication holes that a particular section of bark grows between its cells. These are called plasmodesmata and can only be seen by an transmission electron microscope and range from 30 to 100 nanometers in diameter.
In 2011, researchers Faria, Fonseca, Pereira, and Teodoro made this discovery by identifying that the cork permeation mechanism was porous Knudsen flow and they made the direct correlation to pore sizes and identified the match to these tiny nano sized communication holes. They also found the variability in permeability of cork cut from the same plank of bark with no macroscopic inhomogeneities ranged 3 orders of magnitude and, in fact, was so large that the standard deviation was nearly as large as (and in 5 out of 6 cases larger) than the average in all classes of bark tested.
So, these tiny communication holes are critical in dictating the cork permeability and the tree decides how many holes, where and what size to grow them...and these holes cannot be seen!
NOW, it’s time for the ProCork membrane to step in, because it has similar tiny holes but they are regular and crystalline and coat the cork thereby controlling the variability of gas permeation. The ProCork membrane also does the extremely important job of controlling the extraction of damaging cork tannins which are also very variable in cork and can halt the progression of the normal sensations in the mouth by increasing sourness, bitterness and astringency.
“Permeability of Cork to Gases”, David P. Faria,† Ana L. Fonseca,† Helen Pereira,‡ and Orlando M. N. D. Teodoro† Agric. Food Chem. 2011, 59, 3590–3597
†Center for Physics and Technological Research _ CEFITEC, Physics Department, Faculty of Sciences and Technology, Universidade Nova de Lisboa, Portugal, ‡Centro de Estudos Florestais, Instituto Superior de Agronomia, Universidade Tecnica de Lisboa, Portugal
Contact: Dr Gregor Christie
Text +61 410717081