IJUP08 - Universidade do Porto

Development of a coating barrier for cork stoppers for their use in
spirituous drinks
F. Oliveira 1 , S. Pontes 1 , M. Cabral 2 and A. Mendes 3
1 The Network for Competence in Polymers, Faculty of Engineering, University of Porto, Portugal
2 Amorim & Irmãos Company, Mozelos, Portugal
3 Department of Chemical Engineering, Faculty of Engineering, University of Porto, Portugal.
Presently, spirituous drinks such as vodka are not bottled using cork stoppers, despite the
great appetence of the market for the noble product. The reason for that is the bleeding of
natural colorants present in the cork stoppers to the white drink, making it looks like old
conhaque. Two approaches could in principle be followed to make the cork stoppers
compatible with spirituous drinks. The first one is the extraction of these colorant
compounds leaving a colorant-less cork stopper. The other approach concerns the
development of a food approval and highly flexible transparent coating, impermeable to
the colorant compounds and chemically stable. At first glance none of these approaches
seem to be easy to accomplish. This is indeed true and there is presently no good solution
for this challenge.
The extraction of the natural colorants, namely tannins, from cork stoppers proved only to
delay the color bleeding, even when the extraction was applied to fine cork granules.
Different extracting solvents were employed as well as supercritical carbon dioxide. Some
authors proposed the use of polymers such as silicon [1, 2]. Despite the great permeability
of this polymer, it is food approval, elastic and chemically resistant. It also seems to retain,
sorb, the bleeding colorants from the cork stopper. However, silicon is also not able than
delay the bleeding of colorant to the beverage.
The authors tool advantage of the polarity of the cork stoppers colorants and developed a
coating system considering two layers. The first layer fences the colorants to leave, due to
its charge, while the second layer provides mechanical resistance to the coating. Both
polymers are commercially available and are applied by dip coating. The final coating
system is food approval, very elastic, chemically stable and gas permeable. Moreover, it is
tasteless, transparent and visually attractive. Presently, a new monomer is being
investigated that for developing a polymer that offers complete barrier properties with a
single layer.
References:
[1] WATKINS, S. (1997), Coated cork stopper, WO9711894;
[2] LUMIA, G., PERRE, C., ARACIL, J. (2001), Method for treating and extracting cork organic
compounds, with a dense fluid under pressure, WO0123155;
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