At Penfolds, one of Australia’s most well-known wine brands, the bottling line is an elaborate operation, especially its final stage: the seal. While its white wine range is closed with screw caps, the reds receive different stoppers based on where they are exported.
In Australia, the majority of Penfolds’s red wines, which include offerings priced well into triple digits, are sealed by screw cap. In the U.S. market, however, those same wines are sealed under natural cork. Why? Because many Americans still believe screw caps signify low-quality wine.
As the saying goes, you shouldn’t judge a book by its cover. But should you judge a wine by its closure? Cultural preconceptions aside, the stopper can tell a great deal about the wine it encloses. It can hint at longevity, quality, culture and history.
We spend the most of our time focused on what lies within the bottle. For once, let’s get to know what sits above it. Here’s your guide to the world’s most popular wine closures.
The world’s most widely used wine closure has been around for a while. Evidence of its usage dates back to the ancient Greeks and Romans. However, the close-fitting stopper we’re familiar with wasn’t popularized until the 18th century, in conjunction with the first user-friendly corkscrew.
Renewable resource. Cork is derived from the bark of Quercus suber, also known as the cork oak tree. These evergreens, the majority of which grow in Portugal and Spain, are abundant and strictly protected. Cork oaks regenerate their outer layer of bark, which allows them to be harvested about once every decade. With a lifespan of up to 200 years, one tree can provide cork for thousands of bottles, which makes it the most ecologically sound material to seal a bottle.
Tradition. There’s something romantic and ceremonial about popping a wine cork. The visceral ritual helps cork retain its dominance, even in the face of stiff competition.
Cellar worthiness. Thanks to its elasticity, cork expands within a bottleneck to seal liquid in and keep oxygen out. Its tiny pores, however, allow minuscule amounts of air to interact with the wine, which can transform the aroma and flavor over time. This makes cork the top choice for producers of ageworthy wines.
Susceptible to taint. The chemical compound 2,4,6-trichloroanisole, or TCA, affects mostly wood-derived materials, which makes it cork’s worst enemy. It’s caused when chlorine comes into contact with certain fungi during the cork’s processing. While harmless, the compound can transfer to the wine and cause aromas of wet cardboard, damp basement or wet dog. Known as “cork taint,” or simply being “corked,” past studies have estimated that TCA affects up to 10% of wines under cork, though some producers argue that things have improved.
“Our view is that the TCA problem has been ‘partially solved,’ ” says Peter Gago, chief winemaker at Penfolds. “TCA in cork is down to 1%, comparable to the percentage of screw cap-sealed wines that suffer from oxidation due to mechanical damage of the stoppers.”
Less optimistic studies claim TCA still affects around 3–7% of wines sealed under cork.
Variability. Cork is a natural product, and each is slightly different. Cork brands and their porousness vary, which affects the rate at which air interacts with the wine in the bottle. While winemakers choose corks carefully, there’s always an element of the unknown.
Fragility. Cork is made from wood, which dries out and crumbles with time. Wines cellared for long periods of time must be kept on their sides to keep the cork damp. But even with careful cellaring, how many of us have fished the remains of a crumbled cork out of our wine after it breaks on its way out of the bottle?
Cost. Depending on the quality and brand, corks can be up to three times as expensive as screw caps, which can drive up the final price of the wine.
Not all corks are cut from the same cloth. Meet natural cork’s quirky cousins.
Colmated. Made from medium-grade natural cork, the crevices in these closures are filled in with fine cork powder. It gives the cork a softer texture and smoother exit out of the bottle. Wines can age up to a few years under colmated cork.
Agglomerated. It’s like cork-particle board, where granulated cork dust is bound together tightly by glue and pressure. Agglomerated corks should only be used with wines destined to be consumed young as they tend to break down more quickly. Cork producer Amorim suggests wines sealed with these composite closures be consumed within six months of bottling, though premium options do exist that allow for longer aging.
Multi-piece. When two or more pieces of cork are glued together. Examples include Champagne corks, which expand upon removal and cannot be placed back into the bottle. Other producers also affix discs of natural cork to the ends of agglomerated cork in still-wine enclosures, in order to increase durability. These corks are often made from the manufacturer’s bark “scraps.”
After centuries of unrivaled wine stopper bliss, an unassuming aluminum cap came along and, well, screwed up everything for the humble cork. The Aussies are to blame for stirring the pot.
In 1964, Peter Wall, former director of South Australian winery Yalumba, became fed up with the number of tainted corks in circulation. He commissioned a French company to develop an alternative closure. An aluminum cap, the “Stelvin,” was born, although it wasn’t patented or used commercially until the late 1970s.
Forty-plus years later, screw caps are the closure of choice for the majority of Australian and New Zealand producers, across all styles and price points. It consists of an aluminum cap lined with plastic, which integrates a metal skirt that hugs the top of the bottleneck, just like a traditional stopper’s foil.
Consistency. TCA, the taint that affects so many wines under natural cork, is almost nonexistent under screw cap. Also, because there’s less oxygen interaction with wines in comparison to cork, winemakers can theoretically reduce the amount of sulfur dioxide used as an antioxidant before bottling.
Longevity. Because wines under screw cap reside in a relatively oxygen-free atmosphere, they’re believed to be longer lived. Though long-term studies have shown positive results, it’s a controversial topic within the wine industry. Some argue that with limited oxygen contact, wines under screw cap don’t age at all. Others, like Jeffrey Grosset, owner of Grosset Wines in South Australia’s Clare Valley, say that screw cap enclosed wines age beautifully, just more slowly.
Affordability. Screw caps can vary in price, depending on quality. Generally, however, they’re cheaper than natural cork.
Easy to open. Screw caps open with a simple twist of the wrist. There’s no need for any gadgets beyond a free hand and a little muscle.
Negative environmental impacts. Screw caps are made from aluminum, which is often produced from a strip-mined ore called bauxite. Processing aluminum can be a dirty process, negatively impacting the air and water and generating about 70 million tons of waste annually. Aluminum is non-biodegradable, and though it can be recycled, it’s suspected that most screw caps end up in the trash, and individual waste management companies have their own internal guidelines on whether or not screwcaps are accepted as recyclable. Their plastic liners, if not removed, can also make recycling impossible.
Most screw cap liners are made from Polyvinylidene chloride (PVDC), a plastic that’s unsustainable and toxic when burned. Some, like the California Office of Environmental Health Hazard Assessment, also consider it to pose possible health risks. It’s been banned or restricted in a number of countries in Western Europe. Amcor, the company that makes Stelvin screw caps, recently released a PVDC-free range targeting countries like Germany which have restricted the material. It’s still allowed in the U.S.
Prone to reduction. The opposite of an oxidized wine is a reductive one, or a wine in which there is minimal contact with oxygen during the production process. This can happen when a wine’s sulfur dioxide levels are too high and is characterized by telltale rotten egg/oniony aromas. The topic of reduction in screw-capped wines can be divisive, but it’s generally agreed that the plastic-lined seal itself doesn’t cause these undesirable characteristics. However, the seal can prevent additives like sulfur from being absorbed into the wine the way a more porous cork would, exacerbating the effects.
Questionable aging ability. Cork versus screw cap aging has passionate advocates on both sides. Cork proponents say that the interaction between wine and oxygen facilitated by the naturally porous material is essential to the aging process of a cellarworthy wine. Screw cap fans think otherwise, though neither side has proved their enclosure is better.
Amcor has created multiple liners. One offers more permeability at a higher cost, though the company also offers variations on its original liner with four different levels of “oxygen transmission rates” (OTRs).
Synthetic corks can be made either from petroleum-based plastic or plant-based materials. Plastic corks are made generally from polyethylene, a malleable material that is melted down and turned into “foam” that imitates the porousness of natural cork. Plant-based stoppers are made similarly, but use bio-polyethylene, a bio-based plastic made from ethylene, a byproduct of processing renewable raw materials like sugarcane.
Consistency. Synthetic corks are not prone to TCA taint. They provide predictable oxygen transfer rates and a tight, immovable seal.
Durability. Because they’re not made from wood, synthetic corks don’t degrade or dry out, so there’s no need to store bottles on their sides to keep the cork damp. Synthetic cork also won’t break apart, so there’s no risk of cork crumbs to fish out of your wine.
Affordability. Synthetic cork can be up to three times cheaper than natural cork. They’re often cheaper than screw caps, too.
Negative environmental impacts. Synthetic corks made from oil-based plastics are not sustainable or biodegradable. They can be recycled, in theory, though it often depends on the materials used to make the cork, whether the producer has imprinted the “chasing arrows” logo on their product, and policies of the recycling company used.
Plant-based stoppers use renewable resources and have a lower carbon footprint than their synthetic counterparts, but cost more and are still in limited use.
Hard to open and reseal. Many wine lovers groan at the sight of plastic-based synthetic cork, mainly because it tends to be the hardest wine closure to open, and some can be virtually impossible to put back into the bottle once removed.
Chemical odor. Some wine professionals claim to detect a chemical odor in wines from oil-based plastic corks, particularly if the wine has been in bottle for a while. While reports of these aromas have abated in recent years and don’t affect plant-based stoppers, the potential for off odors may be of concern to some.
Other types of wine enclosures
More wine closures may pop up, or out, of your bottle.
Zork: Created in 2010 by an Australian company, this closure seals with an inner foil that allows for some oxygen transfer. It has a plastic, cork-like stopper that “pops” when removed, just like real cork. The Zork’s most distinctive feature is an outer strip of plastic that coils around the top of the bottle and peels off, not unlike the cap on a gallon of milk. The Zork Sparkling enclosure allows bubbly bottles to be resealed, unlike their natural cork brethren.
Vinoseal: Also known as Vinolok, this elegant, expensive glass stopper was developed by the Alcoa Corporation, but later handed over to Czech glass producer Preciosa. It was released in the European market in 2003. The glass is ringed with plastic to create a tight seal.
Helix: A twist-off cork that requires no corkscrew, created in 2016 by the world’s largest Portuguese cork manufacturer, Amorim, and the world’s largest glass-bottle manufacturer, Owens-Illinois Inc.
Crown cap: The cap of choice for beer bottles, this closure is used by traditional-method sparkling producers to seal their bubbles before disgorging, thanks to the crown cap’s ability to contain pressure. These bottlings are later resealed with cork, wire cage and foil. Many pétillant–naturel (natural sparkling wine) producers that don’t disgorge choose to release their sparklers in all their crown-capped glory. Even some still wines, particularly those in the natural camp, are starting to flaunt the crown cap seal.