It used to be simple. Good wine had a natural cork. Cheap wine had a screw top. Not any more.
The 1990s wine boom stressed cork production and engendered an increase in “cork taint” caused by the chemical compound trichloroanisole (TCA). By some measures, 5% or more of cork-closed bottles exhibited the musty, wet cardboard aromas of cork taint.
The wine industry responded. Natural cork makers focused on sanitation and quality control. The problem lessened but cannot be totally eliminated. Alternatives blossomed, but all closures proved to have some problems.
• Screw tops eliminated TCA, but in low tannin wines there can be a reductive process that produces sulfur odors. Wet cardboard was replaced by rotten-egg smells. Careful use of sulfur and liner improvements have reduced this issue. Today, 90% of wines made in New Zealand and Australia employ screw tops.
• DIAM corks are made by dismantling natural cork into fine
granules, then reconstituting with polyurethane binders. The process eliminates TCA and can be fine-tuned for oxygen ingress. But that fine tuning can introduce variables, including the same sulfur issues as screw tops, muted aromatics, and thin, flat flavors. DIAMs also cost significantly more than natural cork.
• Synthetic corks. Eliminates TCA, but can prevent the micro-oxygenation desired in aged wine. There also is an environmental trade-off. Synthetic corks rely on non-renewable plastic, contributing to microplastic pollution.
• Glass closures. Vino-Lok glass stoppers eliminate TCA and create a seal that virtually prohibits oxygen ingress, a good or a bad thing depending on the wine. The stoppers require significant modifications to a bottling line, a hurdle for smaller producers. They also require specialized bottles, which can cost 20-30% more than a standard Bordeaux bottle.
• Natural corks are made from the renewable outer bark of the cork oak tree. When a tree reaches 25-30 years old, its bark can be harvested every 9-12 years for 200-plus years. Cork closures have been the gold standard in closures for centuries. Cork tree forests sequester a significant amount of carbon dioxide, up to 14 million tons of carbon dioxide annually. Because of the renewal of bark, harvested trees absorb 3-5 times more carbon than non-harvested trees. Cork trees also support Mediterranean biodiversity and sustain rural economies in Portugal and Spain. Deep roots systems stabilize the soil and retain moisture.
Bottom line: there are advantages and disadvantages to each type of closure. Natural cork-based products still close almost half of the world’s wine bottles and 70% of premium wines. Natural corks are not going away any time soon.
Last round: Perfect pairing: I like wine. Wine likes me. Pull the cork, twist the screw top.