Cleaning of Cork

For centuries cork stoppers have been used to seal wine bottles and in the western society, people expect the typical sound blob when opening a botde of wine. Cork is a natural polymer foam based on the substance suberine and grown as bark of the oak tree (Quercus suber). 

Secondary metabolites produced by infections of fungi or bacteria can damage the quality of cork. The worst one is trichloroanisole (2,4,6-TCA) that is primarily responsible for the typical cork taint and causes drastic losses in the wine industry. Good wine specialists can recognize a TCA content in wine of about 2 ng/1, while usual consumers notice concentrations between 5 ng/1 and 10 ng/1. The cork industry made a lot of efforts to solve this problem because it became very serious during the recent years. A number of processes were developed mainly using overheated steam to reduce the TCA concentration in the cork. But even with the best of such plants, a TCA reduction of only 70% can be reached. 

One of the leading cork producers, Sabate, began the development of a cork cleaning process with supercritical gases in 1997 [32, 33]. The tests were very successful and, consequently, the process was patented. With supercritical gas, it was possible to reduce the TCA content below the detectable limit, which is at the moment around 0.2 ng/1. Furthermore, CO2 has special properties regarding reduction of pesticides and inhibition of fungus growth. 

In 2003, NATEX Prozesstechnologie started investigations for scale-up of an industrial process. With a production capacity of 2500 tons per year, it corresponds to 500 million cork stoppers. In order to optimize the energy consumption, a careful comparison between the pump and the compressor process was executed. 

The evaluation showed economic advantages for the compressor process and in consequence design engineering was adjusted accordingly. 

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