Evaluating a bottle of wine often involves determining essential factors such as region, grape variety, and producer. However, one element often overlooked is one of the first things we encounter: the closure. Long before a wine bottle reaches our table, a winemaker has given considerable thought to the seal. Often this decision will provide subtle clues about the producer or the culture of the region. Picking from some of the best wine closures may seem subjective. However, producers weigh the pros and cons heavily when it comes to deciding which one to use.
Mediterranean cork groves have been the world’s leading source of wine cork for centuries. The groves are some of the most bio-diverse and sustainably harvested forests in the world. In addition to having the most extended history, natural cork remains the most popular closure worldwide.
Pros of Natural Cork
- Sustainability – Natural cork comes from the bark of cork oak, a medium-sized evergreen mostly grown in Portugal and Spain. The bark of a cork oak regenerates every nine years and has a life span of 200 years. One cork oak tree provides enough cork for thousands of bottles of wine in its lifetime. Both biodegradable and recyclable, natural cork is the most environmentally friendly wine closure.
- Cellar worthy – The elasticity and permeability of natural cork allows it to expand and seal wine in the bottle (cork’s flexibility is the exact reason that preservation systems such as Coravin work so well). In the cellar over time, microscopic amounts of air enter the bottle. This transfer of oxygen allows flavors and aromatics in the wine to change, often transforming the wine for decades when stored properly.
- Tradition and perception – There is a romanticism to the ritual of opening a bottle of wine with a corkscrew. Traditionalists often cite their preference for natural cork leading to a perception among consumers that it seals higher quality wine. For long-term cellaring, the proven record of cork lends it favorable appeal.
Cons of Natural Cork
- Cork taint – Odds are, at some point, you opened a bottle of wine, wrinkled your nose, and wondered why it smelled of wet cardboard or a damp basement. The culprit in such instances is a chemical compound 2,4,6-trichloroanisole, more commonly known as TCA. This compound forms when plant phenols, chlorine, and mold interact, often during the processing of natural cork, though not exclusively. TCA can also originate in barrels, wooden pallets, and cardboard cases if damp conditions and chlorine mix. Studies reveal that up to 10% of wines with natural cork closures are tainted with TCA. Recent developments in technology have proven successful in eliminating TCA from natural cork closures. Six years ago, one of the world’s leading cork manufacturers, Portugal-based Amorim, set the lofty goal of eliminating TCA by 2021. Its $16 million investment has paid off as their NDtech process of screening offers a non-detectable TCA guarantee.
- Variation – Similar to the subtle ways barrels can differ by cooper, natural cork can also vary by producer. This leads to variability after bottling. Most drinkers smell a cork as part of the ritual when opening a bottle. However, winemakers evaluate corks for aroma and porousness before bottling. Improvements in technology are also working to eliminate cork variances.
- Vulnerability – Natural cork is prone to drying and crumbling when a wine bottle is not stored correctly. It is essential to cellar a bottle on its side so some wine remains in contact with the cork. While this is the best method for long-term cellaring, it does not ensure that a cork might be fragile and prone to crumble even under optimal conditions.
Screw Cap (Stelvin)
Given the historic high rate of cork taint, it is surprising that natural cork reigned supreme for centuries before a challenger came on the scene. It was in 1964 when Peter Wall, former director of Yalumba winery in Australia, commissioned French company Le Bouchage Mechanique to develop a closure alternative. The result was the “Stelvin,” or more commonly, an aluminum screw cap.
Pros of Screw Cap
- Reliability – Unlike natural cork, aluminum screw caps are not prone to TCA. Though not unheard of since TCA can develop from other sources such as barrels, it is rare to open a bottle with a screw cap closure and find elements of TCA.
- Convenience – With a screw cap closure, one will never be left frantically searching for a wine opener when you want to enjoy the bottle! A simple turn of the wrist, and the bottle is ready to pour. Wine producers from Australia and New Zealand were early adopters of the screw cap for both red and white varietals; domestic producers and consumers have not as readily embraced the screwcap.
- Cost – Similar to natural cork, screw caps can vary by price and quality. However, generally speaking, they are much less expensive than natural cork.
Cons of Screw Cap
- Environmental Concerns – Screw caps are made from aluminum, a non-renewable source, and include a plastic liner that must be (but most often is not) removed to be recyclable. Aluminum processing has a significant carbon footprint and uses copious amounts of water and power. The process often involves strip mining to extract bauxite, resulting in the loss of native vegetation, wildlife habitats, and soil erosion. In addition, the plastic liner in most screw caps is made from Polyvinylidene chloride (PVDC), a plastic known to be toxic when burned and considered to pose possible health risks. Though still allowed in the United States, many Western European countries have banned or severely restricted the use of PVDC. In recent years more manufacturers have developed PVDC-free liners, though they are a non-renewable source.
- Oxygen-Transfer – A great way to spark debate at a dinner party, bring an older vintage with a screw top! Advocates for the screw top will argue that limited oxygen contact allows the wines to show minimal signs of age or slight changes over an extended period. Those in the corner of natural cork closures argue that oxygen transfer is an essential element in the aging process. Though several producers have done side-by-side offerings of their wine under cork and screw cap, none has settled the debate on which closure is “better” in the long term. As we know is often the case with wine tasting, different palates, different perceptions.
The Rise of Other Wine Closures
Though not as widely used, there are additional closures that merit a mention.
Composite cork refers to cork particles or cork dust formed with pressure and glue or plant-based binding agent. Several advantages of this type of cork include being TCA-free, allowing for some oxygen transmission, and offering a great price point for value-oriented wines. Composite corks can break down easier than natural cork, and their best use is in wines intended for consumption less than one year after bottling.
Synthetic cork is made from petroleum or plant-based plastic materials and offers the advantage of being TCA-free. Not to mention, it’s durable and affordable. Unlike natural cork or composite cork, synthetic cork will not degrade over time. When crafted from plant-based renewable material, such as sugarcane, this type of synthetic cork is recyclable. The petroleum-based counterpart is not sustainable and rarely recyclable due to the materials used. Synthetic cork tends to be the most challenging wine closure to open.
Vinolok is arguably the most elegant closure. Made of glass, Vinolok is one of the most expensive and labor-intensive options. Bottling lines are generally compatible between cork or screw top closures, so the use of glass closures requires additional resources and time during bottling.
The Helix is a relative newbie on the closure scene. Introduced in 2016, Helix is a joint venture between Amorim and glass-bottle manufacturer Owens-Illinois Inc. Combining the twist-off convenience of a screw cap with the traditional “pop” of a cork, the Helix offers the advantages of both cork and screw cap closures, with the potential to gain traction as a sustainable alternative to aluminum.