Screw Cap or Cork? What Science Really Says
The idea for this research came from a conversation I had over dinner with a colleague. Despite being a professional sommelier, he took for granted a belief that is still extremely widespread: screw caps are mainly suitable for young, immediate white wines, while cork remains the necessary choice for more important wines intended to evolve over time.
What struck me was not that this opinion was particularly unusual. Quite the opposite. It is such a deeply rooted conviction that it is often repeated even by knowledgeable people who work with wine. I therefore decided to investigate what scientific studies, research institutes and producers that have tested both solutions actually say.
This article is the first part of a research project that will continue through several further investigations. The comparison between screw caps and cork involves very different subjects: oxidation, reduction, ageing, closure defects, consumer perception and commercial appeal across different markets.
The first conclusion is already fairly clear: things are not exactly as they are often presented. Screw caps are not a solution reserved for inexpensive white wines, while cork is not automatically the best closure for every wine intended to age.
For more than twenty years, universities, research institutes and producers have been studying the behaviour of different closures, trying to understand how they influence the oxygen inside the bottle, aroma preservation, colour, sulphur dioxide and the overall evolution of wine.
The result is not a clear victory for screw caps or cork. The conclusion is more complex, but also more interesting: there is no single closure that is universally better. There are closures that are more or less suitable for a particular wine, a certain period of storage and the result the producer wants to achieve.
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A closure does more than simply seal the bottle
Wine continues to evolve after bottling. Alongside other factors, the closure regulates the amount of oxygen available and can influence sulphur dioxide loss, oxidation, colour stability and the preservation of aromatic compounds.
When too much oxygen is present, wine may lose freshness, change colour and develop oxidative aromas. When the environment is extremely low in oxygen, however, some sulphur compounds associated with so-called reductive notes may be preserved or encouraged.
The permeability of a closure is often expressed through its OTR, an acronym for Oxygen Transmission Rate. This indicates the amount of oxygen that can pass through the closure over a given period.
This figure is fundamental, but it is not the only factor involved. The oxygen already dissolved in the wine also matters, as does the oxygen remaining in the space between the liquid and the closure, the amount of sulphur dioxide, the storage temperature and the conditions under which bottling takes place.
A study published in OENO One, conducted on a Merlot-Tannat red wine and a rosé using eight different closures, showed that the wine’s shelf life depends on the interaction between the oxygen present at bottling and the permeability of the closure. The closure matters greatly, therefore, but it never works in isolation.
Why Australia and New Zealand turned to screw caps
A significant proportion of the research into screw caps comes from Australia and New Zealand. This is no coincidence. By the end of the 1990s, producers in these countries were looking for a solution to two very practical problems: cork taint and bottle-to-bottle variation associated with natural cork.
In 1999, the Australian Wine Research Institute launched a major trial involving a Semillon bottled with fourteen different closures. During the first twenty months, the wine under screw cap retained more sulphur dioxide and ascorbic acid and showed slower browning. The initial results of the Australian Wine Research Institute trial made a decisive contribution to the spread of screw caps throughout the New World.
The advantage was particularly evident in aromatic white wines, where a loss of freshness and oxidation are immediately noticeable. Screw caps also made it possible to obtain greater consistency from one bottle to another, an important factor for producers focused on export markets.
The spread of screw caps in Australia and New Zealand was therefore not simply the result of a fashion or a cultural rejection of cork. It was primarily an industrial response to defects and quality variations that producers found increasingly difficult to accept.
The main advantage of screw caps: protection from oxygen
The most airtight screw caps greatly limit the passage of oxygen. This allows sulphur dioxide to be retained for longer and slows the degradation of various aromatic compounds.
A study published in 2025 in Food Packaging and Shelf Life examined different closures after twelve years of ageing.
Among those tested, the Saran-Tin screw cap had the lowest oxygen transfer rate. Saran-Tin is a screw-cap closure fitted with an internal seal composed of several layers, including a thin metallic tin barrier. This structure almost completely prevents oxygen from passing through the closure.
In the study, Saran-Tin was associated with better preservation of Sauvignon Blanc varietal thiols and with lower formation of oxidation markers. Varietal thiols are aromatic compounds of particular importance in wines such as Sauvignon Blanc, where they contribute notes that may recall citrus fruit, tropical fruit and boxwood.
Similar results emerge from a study published in Molecules on the evolution of white and rosé wines. In the white wines, samples under screw cap had the lowest levels of dissolved oxygen and a smaller loss of several aromatic esters.
French research has also reached conclusions favourable to screw caps when aromatic white wines are concerned. A doctoral thesis from the University of Bordeaux examined the stability of volatile thiols and found that, in the samples studied, wines closed with natural cork were less stable than those under screw cap.
The Institut Français de la Vigne et du Vin, or IFV, therefore considers screw caps particularly suitable for wines rich in varietal thiols, such as Sauvignon and Colombard, because they provide better protection for aromas that are sensitive to oxidation.
Screw caps eliminate the problem of cork taint
One of the main arguments in favour of screw caps is the absence of any risk of TCA contamination originating from cork. TCA, or trichloroanisole, is the compound most commonly associated with cork taint.
It can produce the classic smell of damp cardboard or a musty cellar, but in some cases it acts more subtly, muting the wine’s aromas without creating a defect that is immediately recognisable.
According to an Institut Français de la Vigne et du Vin technical paper on cork taint, a significant proportion of bottles distributed on the French market may be affected by the problem. Contamination does not concern agglomerated corks alone, but may also involve natural and colmated cork closures.
TCA is not the only compound associated with cork-related defects. A French study on 2-methoxy-3,5-dimethylpyrazine examined another substance capable of producing earthy or potato-like notes. Its presence was not necessarily linked to TCA, showing that the problem of closure-related defects is more complex than is often assumed.
Screw caps eliminate this specific variable at its source. They do not automatically guarantee a perfect bottle, but they allow producers to remove one of the most feared causes of alteration and reduce differences between bottles from the same batch.
The main limitation of screw caps: the risk of reduction
Strong protection from oxygen may also have a downside. Under certain conditions, a highly airtight closure maintains an environment that favours the persistence of sulphur compounds responsible for aromas of rotten egg, cabbage, rubber, struck match or flint.
Sulphur compounds are molecules containing sulphur. Some contribute positively to the aroma of wine, while others produce unpleasant smells when they exceed certain concentrations. These include hydrogen sulphide, commonly associated with the smell of rotten eggs, as well as other compounds capable of producing notes of cabbage, onion, rubber or cooked vegetables.
A study of Riesling and Chardonnay stored for five years found more evident reductive characteristics in wines under screw cap than in those closed with natural cork.
Another sensory trial conducted by the Australian Wine Research Institute associated Saran-Tin screw caps with descriptors such as reductive, cabbage-like and flinty after twenty-four months.
This does not mean that screw caps always cause reduction. The correct conclusion is more cautious: closures with extremely low permeability may increase the risk of preserving or intensifying certain sulphur compounds, especially when the wine already has a tendency towards reduction at the time of bottling.
A study on the scalping of sulphur compounds also revealed an interesting difference between cork and screw caps.
In packaging, the term scalping describes the absorption of certain volatile molecules by the material used to package or close a product. These molecules partially leave the wine and are retained by the closure. Scalping can be a problem when it removes desirable aromas, but it may have a beneficial effect when it reduces substances responsible for unpleasant odours.
In the study, natural cork absorbed part of certain sulphur compounds, including hydrogen sulphide and dimethyl sulphide. Screw caps did not display the same behaviour and therefore tended to preserve more of these compounds when they were already present in the wine.
This finding does not demonstrate that cork always prevents reduction. It does show, however, that the closure material can influence wine not only by controlling oxygen transfer, but also by absorbing certain molecules.
There is no single type of screw cap
One of the most common simplifications is to discuss screw caps as though they were all the same product. In reality, their behaviour depends mainly on the seal fitted inside the cap, which ensures contact and closure around the neck of the bottle.
A Saran-Tin seal uses a thin tin barrier together with additional plastic layers and has very low oxygen permeability.
A Saranex seal, by contrast, is made from multilayer plastic materials and does not contain the same metallic barrier. It therefore allows more oxygen to pass through than Saran-Tin.
Some seals are also made from LDPE, the abbreviation for Low-Density Polyethylene. This is a plastic material with greater oxygen permeability, used when a producer wants to allow more exchange than would be possible with an almost airtight screw cap.
A study on Chardonnay and Pinot Noir compared natural cork, synthetic closures and three different screw caps.
Saran-Tin retained higher levels of sulphur dioxide and maintained more protected conditions. The low-density polyethylene seal, on the other hand, encouraged a greater decrease in some sulphur compounds, probably also because it allowed more oxygen to pass through.
Essentially, the more a closure protects wine from oxygen, the more it slows oxidation. At the same time, however, it may preserve a more reductive environment.
It is therefore inaccurate to say that screw caps are always too airtight. We need to know which internal seal was used and how much oxygen it allows to pass through.
There is no single type of cork closure either
The same reasoning applies to cork. Natural, colmated, agglomerated, microagglomerated and technical cork closures can behave very differently.
Their permeability, consistency, contamination risk and ability to interact with wine all vary. Some modern microagglomerated corks offer very low and consistent oxygen transfer, while natural cork tends to display greater variation from one closure to another.
A doctoral thesis from the University of Bordeaux presents a classification in which some screw caps are actually more permeable than natural cork.
Another study developed at Montpellier SupAgro distinguishes between low-permeability agglomerated corks, natural corks with intermediate values and more open synthetic closures.
The opposition between an airtight screw cap and a cork that allows wine to breathe is therefore too simplistic. Each family contains products with different characteristics, and the material alone does not allow us to predict how a closure will behave.
Does cork really help wine age better?
Cork is often considered the most suitable closure for wines intended for ageing. The underlying idea is that a moderate amount of oxygen may support tannin development, the integration of acidity and the emergence of greater aromatic complexity.
The available research does not allow this idea to be turned into a universal rule. Some wines may benefit from a less airtight closure. Others, by contrast, may develop oxidative notes more quickly.
In trials conducted by the Institut Français de la Vigne et du Vin on wines made without added sulphites, screw caps produced the best results for white wines, while the most favourable sensory assessments for red wines were obtained with less airtight closures, including natural cork, technical cork and permeable synthetic materials.
This is one of the most interesting findings in the entire comparison. It does not demonstrate that cork is better for every red wine, but it does indicate that some wines may evolve more successfully when the closure allows more oxygen to pass through than a highly protective screw cap.
A study conducted in Bordeaux on a Merlot and Cabernet Sauvignon blend stored for ten years confirmed that the closure’s OTR alters the wine’s aromatic composition and the intensity of oxidative notes.
More permeable closures tended to encourage oxidation markers, while more protective closures limited them.
The choice therefore depends on the intended result. Keeping a wine as close as possible to its original condition is not necessarily the same as allowing it to evolve in the most desirable way. At the same time, a greater degree of evolution does not automatically correspond to higher quality.
This distinction is important because it reduces both extremes of the debate. It is incorrect to claim that cork always helps wine age better. It is equally incorrect to conclude that the closure allowing the least oxygen to pass through is automatically the best.
Cork can interact with wine
A cork closure is not completely inert. A study published in OENO One examined the migration of polyphenols from natural and microagglomerated cork into hydroalcoholic solutions.
The researchers detected the transfer of hydrolysable tannins and other compounds. This does not prove that cork always improves wine, but it does show that the relationship between the closure and its contents is more complex than a simple exchange of oxygen.
Depending on the type of wine, the duration of storage and the quantity of substances transferred, this interaction could be beneficial, irrelevant or undesirable. It is an area in which further research is still required.
White, rosé and red wines do not have the same needs
International research points towards a fairly clear trend. Aromatic white wines and rosés, which are particularly sensitive to oxidation, often obtain better results from closures with low oxygen transfer.
Screw caps can therefore protect freshness, colour and varietal aromas very effectively. This is one of the reasons why they spread particularly quickly among producers of Sauvignon Blanc, Riesling and other aromatic white wines.
The situation is more complex for red wines intended for long ageing. In some cases, a moderate amount of oxygen may encourage an interesting sensory evolution and reduce the risk of an excessively closed environment. In other cases, however, greater permeability may accelerate oxidation and shorten the life of the wine.
Colour alone is therefore not enough to determine the correct closure. The idea that screw caps are suitable for white wines and cork for reds contains an element of truth, but turns it into a rule that is far too simple.
The structure of the wine, its tannins, aromatic profile, sulphur dioxide level, expected ageing period and the precise type of closure used all matter.
The scientific verdict
Screw caps offer very practical advantages. They eliminate the risk of cork-derived TCA, reduce bottle-to-bottle variation and protect many wines effectively from oxidation and aroma loss.
Their main limitation emerges when this protection becomes excessive in relation to the characteristics of the wine. A closure with extremely low permeability may preserve certain sulphur compounds more easily and encourage an evolution that is too reductive.
Cork, by contrast, may support the evolution of certain wines in an interesting way, particularly when a moderate supply of oxygen contributes to the intended profile. It nevertheless remains exposed to the risk of TCA, other defects and greater variability, especially in its natural forms.
Research does not therefore crown a winner. It indicates a criterion: the closure should be selected on the basis of the wine, its composition, the expected period of storage and the way in which it is intended to evolve.
The comparison between cork and screw caps is often presented as a conflict between tradition and innovation. It is a simple interpretation, but not a particularly useful one. Cork is now available in natural and technical forms with very different performance levels. Screw caps can also use internal seals with equally different levels of permeability.
The real development is therefore not the automatic replacement of cork with screw caps, or the defence of cork for cultural reasons. It lies in moving beyond the idea that one closure can be suitable for every wine.
The next time we open a bottle, perhaps we should ask ourselves not only what material the closure is made from. The more interesting question is what kind of evolution the producer chose for the wine we are about to drink.
