Stoppers permeability
In the storage of bottled wine people keep talking about the stoppers, which let the wine “breathe” (natural cork) and the “airtight” ones (synthetic stoppers). Nowadays the scientific literature does not report on significant readings on oxygen permeability as regards the different stoppers, therefore, all the notices are directed to empiricism and experience.
In the last five years Korked srl carried out deep studies in cooperation with the University of Udine, comparing the performance of the different stoppers today available on the marketplace.
In each stopper group, the permeability to oxygen has been measured by means of a non destructive system, which measures the oxygen consumption of wine. In this way it was possible to follow the wine evolution in each single bottle for several months.

In the diagram below (Fig. 1) the comparison readings among natural corks, technical corks, synthetic stoppers and “KORKED™ active stopper”. In this case the reference “KORKED™ active stopper” has been equipped with a special membrane for as much oxygen exchange as an excellent natural cork.
The data make us think about the following considerations:

Fig. 1 - Permeability to oxygen in the different stoppers


Natural corks
They show weight variability in each single lot, even worse is the situation among different lots. This weight difference indicates a density difference, therefore different mechanical properties and gas permeability. After these surveys, one or more corks inside the same lot showed an “extreme” behaviour according to the average.
Moreover, the measurings on oxygen permeated by the stoppers is not in function of stopper height or diameter. Stoppers with larger diameter or longer, for example, do not represent the most efficient stopper than smaller diameter or shorter ones.

Cork technical stoppers (agglomerated with edge layers)
The show less variability to oxygen permeability if compared to natural cork. The major risks attributed to this kind of stopper are detected especially during the tasting, when the real problems emerge (stickiness, likelihood to be addacked by TCA, presence of abnormal tastes and gluing substances, etc.).

Synthetic stoppers
The surveys effected on the synthetic stoppers available on the marketplace reveal values of permeability to oxygen completely heterogeneous in the category, moreover they show very high variability. The idea that the synthetic stopper is airtight is today a wrong opinion, clearly denied by the test data. The chosen production process (extrusion, injection, etc.) and the raw material determine the results often completely contrasting this opinion.

KORKED™ active stopper
The surveys show that the compared “KORKED™ active stopper” allow the permeation of an oxygen amount similar to the average value of the considered natural cork. As regards this parameter, “KORKED™ active stopper” shows almost no variation if compared to natural cork and synthetic stoppers. Moreover, no cases have been reported in which “KORKED™ active stopper” shows an “anomalous” behaviour and the oxygen passage values are similar one to the other.

It is important to highlight that the compared “KORKED™ active stopper” is a question of choice, not of consequence, and that the aim of this choice is to reproduce the performances of a high quality cork stopper.

Porbably the permeability to oxygen characteristic of natural cork is not always the best one for the preservation or, better, for the evolution of bottled wine.
In the oenologic world there are often bottling compromises with punctual dosage of anti-oxidantes (sulphur dioxide, abscorbic acid) and oxidation catalyst, with activity directed to the products in reduction (copper ione).
Si assiste spesso nel mondo enologico a strani compromessi in imbottigliamento con dosaggi puntuali di antiossidanti (anidride solforosa, acido ascorbico) e di catalizzatori di ossidazione con attività verso i prodotti di riduzione (ione rameico).

Objective of “KORKED™ active stopper” is to modulate the oxygen passage in function of the wine to be achieved, just like it happens during the production phases. Consequently, for each kind of wine the most suitable “KORKED™ active stopper” will be studied and supplied.

Sensorial Tests
Within the last three years, Korked srl carried out a series of bottlings in thermostatic environments at controlled humidity and temperature, in order to evaluate in fuction of time the sensorial evolution of different wines bottled with different stoppers, which oxygen permeability was previously tested.

The sensorial tests constantly highlighted the relevant differences among the bottled wines, according to the quantity of oxygen permeated through the single stopper: the closer wines were bottled with synthetic stoppers while the opener ones were bottles with natural cork or “KORKED™ active stopper”.
Let’s also highlight that during the tastings, the bottles with natural cork showed defects connected to the presence of TCA and TeCA, in addition to the reduced oxygenation, caused by the stopper itself. Generally speaking, the natural cork does not allow the homogeneous oxygenation of bottled wine.

Korked srl has also set up bottling tests, in order to evaluate the oxygen impact in shorter tines than the bottled wine. Those tests put into comparison the evolution of wines bottled with natural cork, low permeability synthetic stopper and “KORKED™ active stopper” (equipped with high permeability membrane, 8-10 times faster than the previously analized “KORKED™ active stopper”). The preservation of the wines, both white and red, was held in enough extreme temperature conditions: 10°C, 26°C and 35°C. After 4 month’s bottling in these conditions, the sulphur dioxide and the wines were subjected to the sensorial analysis and ordering test.
As regards the free and total sulphur dioxide, here below the graphics which refer to white wine stored at 26°C, as the condition of maximum permeability for the tested membrane (Fig. 2 e 3). The highlight is that also in the bottles stoppred with “KORKED™ active stopper” at high permeability there were no significant difference between the different products.

Fig. 2 - Free sulphur dioxide in the different thesis (membranes 5 to 10 times more permeable than Korked)


Fig. 3 - Total sulphur dioxide in the different thesis (membranes 5 to 10 times more permeable than Korked)


The bottles stoppered with “KORKED™ active stopper” with membrane at high permeability, as already noticed in the sulphur dioxide analysis, even though they did not receive oxygen in higher quantities than needed, they did not show any defeat, or better, they were appreciated by the wine tasters.
For the red wines, a significant difference between the two different stoppering systems was observed: the optical density at 520nm (red colour intensity) is higher in the stopper with the membrane, a confirmation of the fact that the evolution in the bottle needs a certain quantity of oxygen.

Conclusions
We can shortly conclude that:
1) It is difficult to foresee the average permeability also inside a single lot of stoppers in natural cork, as it does not depend either on the size or on the stopper itself.
2) Each single lot of analyzed natural cork shows, in addition to the well known problems coming from TCA, some “external” permeability values completely beyond the typical average variability.
3) The technical cork stoppers (agglomerated with edge layers) do not show permeability values comparable to those in natural cork.
4) The synthetic stoppers can be qualified as a airtight stopper. Inside the category there are examples of high permeability stoppers, but with high variability. The synthetic stoppers can cause situations both of reduction and oxidation of the bottled wine.
5) The “KORKED™ active stopper” is constant to permeability and at the same level of good quality tested natural cork. In the forced oxygenation tests the sensorial differences are not correlated to the free sulphur dioxide, which is submitted to variations of some mg/L only.
6) It is not certain that the oxygen permeability characteristic of natural cork is always the best one for the correct evolution of bottled wine. The objective of “KORKED™ active stopper” is to control the passage of oxygen in function of the wine to be achieved. Consequently, for each kind of wine the most suitable “KORKED™ active stopper” will be studied and supplied.

Reports
The “KORKED™ active stopper” characteristic is to measure the correct micro-exchange of oxygen with the external environment according to each kind of wine and its characteristics.
The objective is to enable the ideal refinement of the wine in a bottle.
Consequently, for each kind of wine the most suitable “KORKED™ active stopper” will be studied and supplied. This is the reason why the University created a sophisticated methodology to determine the gas micro-exchanges, in order to precisely measure the effective oxygen absorption in each bottle of wine. The oxygen quantities exchanged in settled periods allow to compare the performances of the different kind of membranes in the “KORKED™ active stopper”, as expressed in the following graphic.

The oxygen absorption (y-axis) is measured for the different kinds of membrane used in the “KORKED™ active stopper” and in function of predetermined regular intervals (x-axis).
The straight lines in different colours shown in the diagram indicate the linear regressions of the points corresponding to the measured values for each membrane.
On two of them the equation and the regression coefficient R² were indicated (for R2 and R1 the straight line correctly interpolate the data).
Now it is evident that the differenc of behaviour among the different kinds of considered membranes.