Screw cap or cork, without the dogma.

The screw cap versus cork argument is usually conducted as a matter of faith, with tradition on one side and reliability on the other. Neither side is quite right. Both closures can carry a fine wine through years in bottle. They do it differently, fail in different ways and need different storage. Those differences matter more to you than the ceremony of pulling a cork.

The real variable is oxygen. A closure decides how much air reaches the wine over the years and how evenly it does so from one bottle to the next. Everything else follows from that: how the wine ages, which faults you may meet and how the bottle should lie in your cellar.

Natural cork: tradition with variables

A natural cork is punched from the bark of the cork oak. It seals by pressing outward against the neck and lets in tiny amounts of oxygen over the years. The trouble is that the amount varies from cork to cork: the Australian Wine Research Institute (AWRI) notes that natural corks can vary widely in how much oxygen they let through. That variation is the main reason two bottles from the same case can taste different after fifteen years. It is also why one disappointing old bottle is not a verdict on the wine.

The second variable is cork taint. The compound mainly responsible, TCA, smells musty, like damp cardboard or a wet cellar. Sensitive tasters can pick it up at one or two billionths of a gram per litre. At low levels it may not smell musty at all; it mutes the fruit, so the wine seems dull rather than faulty. How often it happens is disputed, because the cork industry and its critics count differently, but most published figures suggest taint has become less common since the early 2000s. How to tell if wine is corked explains what to do when you meet it.

A cork does not last for ever either. Over decades it loses its elasticity and seals less well, letting more wine out and more air in. On an old bottle, the gap between wine and cork is largely a record of how the cork has behaved.

Technical corks

Technical corks are made from cork granules bound together, from coarse agglomerated stoppers to fine micro-agglomerated ones. The cheapest agglomerated stoppers suit only wine meant to be drunk soon after purchase. The better ones are treated against the compounds behind cork taint. They are also more consistent: the AWRI rates them at low to moderate oxygen transfer, with less variation than natural cork.

They are widely used, on everyday bottles and serious wines alike, by producers who want the feel and ritual of cork with far less of its lottery.

Screw caps

A screw cap is the most consistent of the common closures. It lets through very little oxygen and does so almost identically from bottle to bottle. How much gets through depends on the liner inside the cap: a liner with a layer of tin lets through almost none, while an all-plastic liner lets through slightly more.

In New Zealand and Australia the screw cap is the standard closure, on many of the best wines as well as everyday ones. In 2000, thirteen Clare Valley winemakers sealed part of their Riesling under screw cap together; today an Australian Riesling under cork is a rarity.

The long-term evidence is encouraging. In a trial run by the AWRI, fourteen closures sealed the same Sémillon in 1999. The screw cap kept the most protective sulphur dioxide in the wine, kept its fruit freshest and browned it least. Photographs of the bottles taken up to ten years later showed the screw cap, along with one of the technical corks, still ahead.

There are two caveats. The first is reduction. With so little oxygen getting in, some wines develop reductive notes: struck match, rubber, occasionally rotten egg. In that same trial a rubbery note appeared under the screw cap after about eighteen months. Yet a decade of results from a large international wine competition, reported by the AWRI, found reductive faults no more common under screw cap than under cork or synthetic stoppers. Such notes often fade with air, so if a screw-capped wine smells of struck match, decant it before you judge it.

The second caveat is that a screw cap removes cork as a source of taint but not every source. TCA can also come from barrels and other wood in the winery, so a screw-capped bottle is not guaranteed to be clean.

Synthetic stoppers, glass and wax

• Synthetic stoppers. Plastic corks are fine for wine meant to be drunk young. They typically let in more oxygen than a technical cork or a screw cap, which is why you rarely see them on wines built to age.
• Glass stoppers. A glass stopper seals on a thin, inert plastic ring. It needs no corkscrew, reseals neatly and carries no risk of cork taint. It reached the market only in 2003, so its record over decades is still being written.
• Wax. A wax seal covers the top of the cork in place of a foil capsule. It looks handsome, but the cork underneath still does the sealing. Wax also hides the seepage and staining you would otherwise check for. To open, cut the wax away or drive the corkscrew straight through it, then brush the crumbs from the neck before the cork comes out.

Screw cap versus cork in the cellar

The closure decides how a bottle should be kept.

• Cork, natural or technical: on its side. Lying down keeps the wine against the cork so it stays moist and does not shrink, provided the air around it is humid too. Years standing upright in a dry room is the classic way to ruin a cork.
• Screw caps: either way. There is nothing to keep moist, so they can stand.
• Heat: bad for everything. No seal keeps a wine cool. A bottle that spends a summer in a hot flat is damaged whatever is in its neck, which is why storing wine in a hot climate matters more than the choice of closure.

Old corks bring a question of their own. Some estates recork old bottles for their owners: each bottle is checked and topped up, ideally with the same wine, then fitted with a new cork and capsule. What matters is who did the work and whether it was documented, since topping up is also where fraud can enter; what fill levels tell you lists the questions to ask. When you finally open a bottle with an original cork of thirty years or more, expect it to be fragile and use the tools and patience described in opening an old bottle.

What the closure does not tell you

Cork and screw cap both seal ordinary wine and great wine. Many of the finest Australian and New Zealand wines are under screw cap, while plenty of forgettable bottles carry a natural cork. What a closure mostly reflects is the producer's priorities and the market the wine was made for.

The closure tells you how to store a bottle, not how good the wine is.

Its practical messages are worth reading: roughly how evenly the bottles will age, which fault to suspect if something seems wrong and how to lay down the case. For any wine you plan to follow over the years, natural cork's variation is one more reason to buy several bottles rather than one; which wines improve with age helps you choose them. To settle the argument for yourself, find a wine bottled under both closures and compare the two in a blind tasting.

The rules that follow are short. Lay anything with a cork on its side somewhere cool and humid. Let screw caps stand if that is easier. Give a reductive young wine air before you judge it. Return a musty bottle rather than drinking around it. Then choose the wine for what is in the bottle.