As discussed in the titled article "The importance of oxygen permeability" published in the April 2020 newsletter of the ICSURO Foundation, there are several methods to determine permeability.

Currently, there is no proven and standardized methodology for the measurement of OTR and it is difficult to assess OTR values for different coverings. The first OTR analytical technique for the caps was the Mocon Oxtrans (Figure 1). This technique was based on the regulation of plastic containers ASTM-F107-14, by measuring the oxygen that was transferred through a bottle neck sealed to a metal plate and by measuring the entry and exit of gases by techniques barometric This technique has several limitations, as it is destructive, expensive and with short monitoring.

Figure 1. Device for measuring the permeability of closures according to the Mocon method. source Dieval, JB. and in 2011

Years later other techniques came out such as those based on bisphenol (Skouromounis et al 2007) or colorimetric (Lopes et al 2005) (figure 2 and 3). Both methodologies are non-destructive techniques, but they require specialized and expensive equipment that makes it difficult for them to be routine techniques. At the same time they do not give direct readings but require an extrapolation to a theoretical model.

Figure 2. Device to measure the permeability of enclosures according to bisphenol. source Skouromounis et al 2007.

Figure 3. Calibration diagram of the colorimetric method based on the reduction of indigo carmine. source Lopes, P. et al 2005 in .J Agric. Food Chem. 2005, 53, 6967-6973 6967

Later, the manometric method was developed, based on passing air under pressure through a piece of 3mm cork (Lequin et al 2012) (Figure 4). This technique made it possible to obtain the diffusion coefficient of O₂ of that material and not the OTR. The results of this technique are difficult to extrapolate as a routine assay, and it is also a destructive technique.

Figure 4. Diagram of the manometer to measure the transfer of oxygen through the cork.. Source. Lequin, S. et al 2012. In J. Agric. Food Chem. 2012, 60, 3348−3356

Finally, the chemiluminescence or oxoluminescence technique was described (Diéval et all. 2011). Chemiluminescence is a non-destructive method and allows you to track a cap over the months by directly measuring the amount of oxygen inside the bottle (Bunner et al., 2010). This technique is the theoretical basis of the oxoluminescence devices that we can find on the market.

The device used in the GO OTR project is called NOMASense and consists of an electronic device with a transmitter and receiver probe (Fibox 3 LCD Trace V6), which emits a green luminous flux or pulse. This flow is directed to a sensor stuck inside the transparent container (bottle). The sensor is made up of fluorescent compounds that absorb the energy sent by the probe and return it in the form of light. The measurement is based on the fact that the oxygen concentration in the bottle is inversely proportional to the return time of this light. The result is expressed directly on the screen of the device as partial pressure of oxygen inside the bottle (PO₂).

Figure 5. NOMASense, device for oxoluminescence measurements. Source ICSURO.

The NOMASense is an easy-to-use, inexpensive device that measures the OTR of both full and empty bottles over time (Figure 5). It is the technology that is most similar to reality, so the results obtained can be extrapolated. These advantages over the other methodologies have led the last published articles on OTR in capping to use it (Chevalier et al. 2019).

As part of this research, in 2017 an operational group was set up made up of 4 companies producing corks from the Catalan cork sector. Two of which companies, J. VIGAS SA, and MANUEL SERRA SA, produce mostly natural cork stoppers. And the remaining two, TESA SA and FRANCISCO OLLER SA, produce agglomerated cork stoppers with two discs for sparkling wine. The project is called "Pilot project for the determination of the evolution of oxygen permeability along the different manufacturing conditions of corks and the effect of this parameter on still and sparkling wine ( GO OTR)”.

The project has made it possible to determine the variables of the production process that affect the oxygen permeability of corks and that will predictably have a significant effect on the evolution of the different types of wines and sparkling wines.

It is a project co-financed by the European fund FEDER and the Department of Agriculture, Livestock, Fisheries and Food of the Generalitat of Catalonia through Operation 16.01.01 (cooperation for innovation) of the PDR of Catalonia 2014-2020.