Put a Cork in It?
Wine drinkers are divided over whether it’s better to cork a bottle of wine or cap it. But there are several types of cork, each with different performance and environmental impacts, and screw caps are not the only alternative to cork.
The classic natural cork wine stopper is the first that comes to mind. But there are also granulated corks made of leftover granules from the natural cork manufacturing process. Technical corks are made from a combination of natural and granulated cork. Synthetic corks can be made from any number of materials, such as rubber, plastic, and even bioplastic.
Screw caps, or Stelvin caps, are made from aluminum with an interior plastic seal.
You might remember Steve Martin asking Kermit the Frog if he would like to smell the bottle cap in The Muppet Movie. Many servers now “hold the cap and turn the bottle,” but the association of screw caps with low-quality wine has been hard to shake, even though corks and screw caps are both available at every price point.
Many winemakers hold that the tighter seal of screw caps is preferable for preserving young wines, while correctly aging a wine requires porous cork. That idea is now contested.
Cork enthusiasts point out the ecological and cultural benefits of cork forests. Harvesting cork preserves forestland from development, while the impacts of aluminum extraction are severe. A peer-reviewed life cycle analysis confirms that aluminum screw caps require less water to produce than other stoppers, but produce the most greenhouse gas. Whole-piece natural cork production has the lowest climate impact. Plastic stoppers fall somewhere in the middle.
Most wine stoppers are not easily recyclable. Recycling programs are unlikely to accept synthetic corks because it’s usually impossible to tell what material they are made from. The plastic liner that gives Stelvin caps such a good seal also dooms them to the garbage bin in most communities. (Tip: remove the plastic liner and recycle the aluminum caps where you recycle scrap metal. Find a location near you with Earth911 Recycling Search — just enter your ZIP code.)
Granulated corks comprise up to 25% nonrecyclable glues and binders. Although technically biodegradable, natural corks do not break down easily and most municipal composting programs will not accept them. Consider upcycling this durable material or look for a Cork ReHarvest or Recork collection point near you. You can also mail corks to CorkClub, but you must pay the shipping.
Wasted wine is a bigger problem than unrecycled stoppers. Cork stoppers are susceptible to improper storage conditions and cork taint, a fungus that ruins the flavor of wine. Industry improvements have significantly reduced the occurrence of cork taint, but it still affects between 3% and 6% of cork-stoppered bottles.
One alternative stopper that has a lot going for it is also one of the oldest — glass. Glass has been around for millennia, but it has only begun to be used for wine stoppers in the past few years. Designed to look like decanter stoppers, they provide an elegant presentation with no risk of cork taint. Thanks to a plastic gasket, glass stoppers provide as tight a seal as a screw cap. The glass used to make stoppers is stronger than the bottle it seals and is recyclable. The stopper can be used to reclose a half-finished bottle of wine (although the seal will not be as tight), or can be reused as a stopper for home-bottled dressings and syrups.
Unfortunately, the materials and bottling processes are more expensive for glass than for either cork or caps, which has greatly slowed the adoption of the glass stopper. For now, you are most likely to find glass stoppers on a limited number of “lifestyle” wines where aesthetics are as important to the brand as flavor or ecology.
The life cycle analysis did not account for loss due to spoilage in corked bottles. It’s unclear whether that would cancel natural cork’s lowest overall production impact. Thanks to the availability of cork collection programs, cork probably maintains its advantage. Overall, the difference among stoppers is probably not enough to impact your choice of wine. But the bottle itself merits further consideration.
Originally published on February 12, 2019, this article was updated in January 2023.