I've been asked frequently about our choice in using natural cork as the closure in our wine bottles as well as other alternative closures options. There is a fair amount of buzz in the industry and consumer world on closures and acceptance varies quite dramatically by country. I've decided to use this blog post to briefly answer the question why we use cork and also compare it to two leading alternative closures: screw caps and synthetic cork.
Natural cork's largest criticism is trichloroanisole (TCA). TCA is a musty compound (think wet newspaper) that can be detected at startling low levels (a few parts per billion which is equivalent to a few drops in an Olympic size swimming pool) and affects some 1-2% of wine under cork (this percentage varies and is in part dependent upon procedures used in the manufacture of the cork closure). One should keep in mind TCA can come from sources other than the closure itself: water, wooden pallets, the building structure, and that the problem is inflated by chlorine based cleaners. As such, it is possible to have a "corked" wine even when using alternative closures. At the same time it is possible to have a completely TCA free closure when using materials other than cork, and in some cases with properly treated cork.
The second concern with any closure is oxygen transmission rates, I touched on this topic briefly in my last post on Oxygen (http://www.SettembreCellars.com/Blog-Oxygen). Screw caps, or rather their tin and/or plastic liner, allow very little oxygen transmission and can result in reductive aromas (some studies have suggested this affects 17% of wines under screw cap and this percentage is likely decreasing over time as winemakers learn to prepare the wine for this closure type). Natural corks, through years of traditional use, have proven to provide a fantastic seal for bottle aging when stored properly due in part to their ability to seal the bottle and store a minute amount of oxygen to enable bottle aging. Synthetic closures to date have a very poor ability to seal a bottle from oxygen, and are typically not recommended for storage of wines over 9 months (keep in mind this is from when the bottle is sealed at the winery). Synthetics strive to decrease oxygen transmission to provide an age-worthy closure and screw caps strive to understand the precise amount of transmission required for aging. In this regard the only shortcoming of cork is that of being a natural product and thus having some natural variability. We use a premium top grade “Flor” cork in our wines to minimize this variability.
Cork is renewable and biodegradable. Plastics, which are used in the liner of screw-caps and to form the synthetic cork, are not biodegradable. The plastics, a petroleum product, are not renewable and although the metals of the screw cap can hypothetically be recycled they must be initially mined, in reality most recycling services to my knowledge do not accept screw caps. The carbon footprint in producing screw-caps is over 4X that of natural cork even before considering the ability of the cork tree to sequester carbon dioxide and preserve a centuries old ecosystem. Remember that the material we know as cork is made from cork tree bark which is peeled off of the tree once every 10-15 years, the tree is not cut down to harvest the cork.
Any closure must provide an acceptably low level of flavor scalping and/or leaching. Although plastics in general show little adsorption (in-fact a positive spin is that they can adsorb TCA) they do leach into the products. A number of health concerns are present due to the migration of materials from plastics: Antimony trioxide (respiratory irritation, skin irritation, miscarriage, and development delays in children) from PET, dioxin (a carcinogen) from PVC, and bisphenol-A (carcinogen and obesity) from polycarbonate. Although HDPE and LDPE have not yet been proven unsafe, there is undoubtedly an aromatic difference to water that has been stored in a warm plastic bottle. Furthermore, plastic migration can be significantly worse at higher temperatures which is one reason why all of our wines are fermented in stainless steel tanks (or French Oak Barrels).
With our efforts to produce age-worthy wines capable of extended cellaring we currently prefer traditional cork (solid, not the cork particle based variety). Beyond the ability to properly age a wine, provide a good seal, environmental impact, and health related reasons there is also the traditional, aesthetic, and experiential reasons. I love the process of opening and enjoying a bottle of wine stored under a cork closure. For me, it's part of the pleasure of enjoying fine wine.