Composite stoppers for wine bottles
Spanish research organisation Tecnalia is designing composite wine stoppers to combine the benefits of plastic and biomass elements including cork.
The project is named Placotop. ‘We are working on a composite material with all the advantages of cork and plastic,’ says Javier García Jaca at Tecnalia, in the Basque country. ‘We consider that the main disadvantage of natural cork is the price and that of plastic stoppers is their environmental performance, because they are based on fossil fuel resources.’
Natural cork also has another drawback, alone or in composites – it is vulnerable to contamination from trichloroanisole (TCA), which leaves wine with a highly disagreeable odour. Winemakers have invested in research to stop their products being tainted or ‘corked’ in this way, but at least one per cent of bottles are still affected, according to Portuguese cork-maker Corticeira Amorim. Screw-tops and plastic stoppers have their own problems – they can be sensitive to sulphidisation and other kinds of tainting.
A study carried out by Pricewaterhouse-Coopers for Corticeira Amorim found that a plastic stopper produced 10 times the greenhouse gas emissions of a cork over its lifecycle, while an aluminium screw cap produced almost 25 times as much. The World Wildlife Fund has urged shoppers to choose natural cork to sustain the forests where it is grown, home to a unique range of wildlife from vultures to lynx.
Coming to fruition
The Spanish group is not the first to create composite stoppers – France’s Oeneo has already done so with its DIAM range, which is made mainly of natural cork but incorporates plastic too.
Oeneo has invested in a complex treatment process to minimise taint. Its cork is washed with CO2 in a supercritical state above 31°C and 73bar pressure, in a process similar to that used to remove caffeine from coffee beans. This extracts nearly 150 compounds from the cork, including TCA. The Placotop researchers will have to contend with similar problems.
Three research teams are collaborating on the Spanish project. Tecnalia develops trial stoppers and carries out the basic physical and mechanical testing. A French team at Rescoll, in Bordeaux, tests the chemical and sensory properties of the stoppers. Finally, back in the Basque Country, Plásticos Urteta, who already manufacture stoppers for the market, look at how the product can be commercialised.
‘The properties analysed are dimension tolerance, density, humidity, recovery after compression, extraction force and liquid tightness. Besides this, there are requirements for the TCA transference from the stopper to the wine,’ says Garcia Jaca.
Another crucial quality is the oxygen transfer rate (OTR) – a drawback of plastic is said to be that it does not allow oxygen to diffuse in and out of the bottle so that the wine can ‘breathe’.
‘Wines are always going to change after bottling,’ says Jamie Goode, author of Wine Bottle Closures. He suggests that the OTR of hybrid stoppers makes them most suitable for dense red wines that need continued oxygen exchange in the bottle. ‘Red wines destined to be drunk earlier in their life benefit from a closure with a relatively high OTR. Studies consistently show that red wines don’t show negative effects from the higher OTR for at least the first couple of years after bottling and possibly longer.’
Initially, the new stopper from Tecnalia is expected to be more expensive than plastic. ‘The objective of the project is to compete with plastic stoppers in price – that is, a few cents per stopper,’ says García Jaca.
‘However, we know that it will be more expensive, which will be compensated by its better performance. The new material provides several advantages, like lower density, lower extraction force and better environmental performance than plastic.’
The product is to be patented in a few weeks. Commercial production is expected by the end of 2011.