Cork, screw cap or synthetic closure: how each one affects wine

Why the closure matters

After bottling, the only oxygen a wine receives comes through or around the closure. A little oxygen can help some reds soften. Too much flattens fruit and browns colour. Too little can leave wine smelling reduced, with struck match or rotten egg notes.

The measure that matters is oxygen transmission rate, how much oxygen passes through the closure over time. Closures differ widely on it. Natural cork varies even within one batch.

Natural cork

Natural cork is still the closure most people picture when they think of wine. It is punched from the bark of the cork oak, grown mainly in Portugal and Spain. It is elastic, it seals well and buyers associate it with quality.

• Strengths. Tradition, a premium image and a slow, small oxygen ingress that suits long-aged reds. The ritual of pulling a cork still matters to many restaurant guests.
• Weaknesses. Variation from cork to cork, so two bottles of the same wine can age differently. Risk of cork taint from TCA (2,4,6-trichloroanisole), which gives a musty, wet cardboard smell. Corks can dry out if bottles are stored upright for long periods.

Technical corks, made from cork granules bonded together, sometimes with natural discs on the ends, are cheaper and more consistent. Some are treated to reduce TCA risk.

Screw caps

Screw caps are aluminium caps with a liner inside the top. The liner sets oxygen ingress. Tin-based liners let in very little oxygen. Saranex-type liners let in more and suit wines that benefit from some air.

• Strengths. No cork taint. Very consistent bottle to bottle. Easy to open and reseal, which helps restaurants pouring by the glass.
• Weaknesses. Low-oxygen liners can leave reductive aromas if the wine goes into bottle with sulphur compounds already present. Some buyers still see them as cheap, though that view has faded where screw caps are common, such as Australia and New Zealand.

Screw caps need bottles with a matching screw finish and a capping head, so the choice also affects your bottle supply and bottling line.

Synthetic closures

Synthetic stoppers arrived as a response to cork taint. They are made from plastic polymers, either moulded or extruded. They look like corks and use the same bottles and corkers.

• Strengths. No TCA, consistent, inexpensive.
• Weaknesses. Many let in more oxygen than cork or screw caps, so they suit wines meant to be drunk within a year or two. Some are hard to extract and reinsert.

The Indian conditions problem

Most closure research comes from cool wine countries. India is different. Heat changes the calculation. Wine expands as it warms. In a truck or a shop at 35 °C, pressure inside the bottle rises and can push wine past a cork, leaving a sticky capsule and a seepage path for oxygen. Screw caps resist this better.

A closure cannot rescue a broken cold chain, though. Our guide to wine storage and the cold chain in India covers the rest of the journey. Heat damage is also a leading cause of the oxidised, cooked notes described in our wine faults guide.

How to choose

• Fresh, aromatic whites and rosé for early drinking. A screw cap with a liner chosen for low to moderate oxygen keeps them bright.
• Everyday reds for drinking within two years. Screw cap, technical cork or a good synthetic all work.
• Premium reds meant to age. Quality natural or technical cork, with careful supplier testing for TCA.

Run a trial before you switch. Bottle the same wine under two closures, store both sets in the conditions your wine will meet in the market, then taste them side by side after three, six and twelve months. Whatever you choose, manage dissolved oxygen and free SO2 at bottling. The closure only controls what happens after the bottle is sealed. Oxygen picked up during filling, from a poorly purged bottle or a leaky filler valve, is often larger than anything the closure lets in during the first year. Brewers face the same packaging trade-off, set out in our guide to cans versus bottles.