Wine Bottle Storage: Vertical vs. Horizontal Storage - Which is Correct?

When storing wine, there's probably one question that everyone has wondered about at least once: how should the bottle be positioned?

Should wine bottles be stored horizontally, or should they not be stored vertically?

A quick search reveals many explanations stating that bottles sealed with cork should be stored horizontally to prevent the cork from drying out. On the other hand, bottles with screw caps or those using synthetic corks made from plastic-based resins are said not to require horizontal storage since they don't deteriorate due to drying.

In 2018, a major challenge was thrown at these storage methods, which are considered common sense in many ways. The statement came from the head of research and development at Amorim, the world's largest cork manufacturer. The content was striking: "Storing cork-sealed bottles horizontally serves no purpose and may even be harmful."

When examined in detail, many surprising facts emerge regarding wine storage methods and corks. Today, we'll explore the positioning of wine bottles during storage from among these various findings.

Why Doesn't Cork Dry Out Even When Bottles Are Stored Vertically?

"Bottles must be stored horizontally to prevent the cork from drying out." This is something very commonly said about wine storage.

However, the head of research and development at the cork manufacturer dismissed this as unnecessary, calling it "merely folklore." What does this mean?

According to this expert, what matters is the humidity inside the bottle.

The humidity in the headspace—the space between the wine's surface and the cork that seals the bottle—is 100%. Moisture is supplied to the cork from this space, so there's no risk of the cork drying out, and there's no need to store bottles horizontally, according to his opinion.

Rather, when bottles are stored horizontally, keeping the cork constantly immersed in liquid accelerates cork cell deterioration and increases the risk of compromising cork functions such as flexibility, which is crucial for sealing. This is similar to how a sponge becomes brittle when left in water for extended periods.

Structure and Characteristics of Cork

Cork is known to structurally contain a large amount of air. These air layers act as cushioning material, maintaining cork's characteristic flexibility.

This is very similar to bubble wrap, commonly known by the name "puchu-puchu" in Japan.

Bubble wrap achieves very high flexibility by creating many air bubbles on a sheet. However, when these bubbles are crushed, the flexibility disappears and the volume becomes much smaller. Cork works the same way. When the cellular structure maintaining the air bubbles breaks down, air escapes, making it hard, and the volume contracts.

It's also said that a certain amount of oxygen entering wine bottles doesn't permeate through the cork itself but passes through the interface where the cork contacts the bottle. When cork cells break down and volume contracts, the amount of air passing through this interface increases, and in the worst case, it can cause liquid leakage. Therefore, maintaining cork flexibility is crucial when storing wine bottles with cork closures.

Cork Gets Wet Even When Stored Vertically

Even so, vertical storage still feels worrisome. It wouldn't be strange to think so.

However, in reality, it has already been proven that cork gets wet even when bottles are stored vertically.

At least within the scope of the author's research, no reports have been found that numerically measure cork moisture levels comparing horizontal versus vertical storage. However, some reports have measured the degree of liquid penetration into corks through visual confirmation and reported these conditions. According to these reports, even corks from vertically stored bottles showed liquid penetration, albeit with some differences compared to horizontal storage.

This proves that moisture is supplied to the cork even in vertical storage, and simultaneously demonstrates that cork is protected from drying out even when stored vertically, regardless of the underlying mechanism.

Is Horizontal Storage Really Bad?

The head of Amorim's development department points out that storing bottles horizontally may accelerate cork deterioration. Does this mean storing wine bottles horizontally is bad? When looking solely at wine "oxidation," this isn't necessarily the case.

No differences in oxidation tendencies have been confirmed between horizontal and vertical storage, at least for storage periods of about 5 years.

The troublesome aspect here is that currently, we cannot definitively say there "is a difference" or there "is no difference."

Reports to date show that some numerical differences appear between horizontal and vertical storage. However, these aren't clearly significant, remaining at the level of "tendencies that seem likely to emerge."

Furthermore, regarding the progression of free SO₂ and total SO₂ content—indicators commonly used to measure wine oxidation—no differences were observed between horizontal and vertical storage, at least over a 5-year storage period.

"Bottles must be stored horizontally to prevent cork from drying out" is essentially an oxidation prevention perspective. If cork dries out, it causes air and oxygen to enter the bottle. This oxygen then causes wine deterioration (oxidation). Therefore, cork shouldn't be allowed to dry out. That's the logic.

Since there are virtually no differences in various indicators of wine oxidation whether stored horizontally or vertically, one answer might be that either storage method is acceptable.

However, when looking at aspects other than oxidation, the story changes somewhat.

Cork Takes Away and Gives Aromas

Cork stoppers are commonly used for purposes other than sealing wine bottles. In such cases, haven't you ever noticed the aroma of stored contents coming from a cork stopper that had been used to store something with a strong scent?

While you might know this from experience, you may not have consciously thought about it, but cork has the characteristic of adsorbing certain aromas. Conversely, aromas that were on the cork can transfer to the stored object. This becomes clearer when considering TCA, or cork taint, known as a wine defect.

Cork mediates aromas.

Additionally, cork is a wood product. This should remind you of wooden barrels, famous as wine aging vessels. Wooden barrels transfer aromas and phenolic compounds to wine. Recent research has revealed that the same thing happens between cork and wine.

In other words, cork has the potential to change wine's taste and aroma. This characteristic is more pronounced when cork and wine are in direct contact.

Even without direct contact between cork and wine, cork can potentially adsorb wine aromas and add aromas like TCA to wine. However, the degree and nature of this effect change depending on whether actual contact occurs.

If you want to avoid cork's influence on wine's taste and aroma, vertical storage where wine and cork don't directly contact would be more suitable.

Do External Aromas Transfer to Wine?

We've learned that contact between cork and wine can potentially add the cork's original aromas and flavors to wine, or cause wine aromas to be absorbed by the cork. But does cork also transfer aromas from outside the bottle to the wine?

The answer is: "The possibility cannot be denied."

Verified experimental results clearly show that at least synthetic corks allow external aromas to permeate through the stopper and transfer to the wine inside the bottle. However, with natural cork, no aroma transfer to the wine inside the bottle was confirmed.

While wine impact wasn't confirmed, aroma adsorption and penetration into cork was verified. Adsorption was highest in the cork's surface layer, and even in the middle layer, though the amount was considerably less, adsorbed aromatic compounds were detected.

This penetration could progress further depending on the type and amount of aromatic compounds outside the bottle and contact time with cork, potentially reaching the wine eventually. This possibility cannot be denied.

Summary: How Should Wine Ultimately Be Stored?

Most importantly, storage temperature is crucial. Most chemical reactions accelerate as temperature increases. Wine follows the same principle. Storage in high-temperature locations accelerates both deterioration and aging.

Regarding direct sunlight, while most glass used for wine bottles has UV-cutting specifications, exposure to sunlight causes wine temperature to rise, so it should still be avoided.

If we accept the premise that cork doesn't dry out due to external factors, humidity becomes less of a concern. However, if the external environment is extremely dry, the possibility of more moisture escaping from inside the bottle through the cork cannot be denied.

Incidentally, even in oxygen-free environments, storing wine in high-temperature locations accelerates wine deterioration. Temperature is more important than oxygen presence.

Factors that significantly influence wine aging and deterioration are the type of closure and oxygen content in the headspace. However, consumers cannot control either of these factors. In other words, these are aspects not worth considering when storing wine you've purchased.

Generally, the ideal storage temperature for wine is said to be around 15°C. Constant stability within this temperature range is most important for wine storage.

For bottle positioning, either vertical or horizontal storage is acceptable for periods of about 5 years. However, for longer-term storage or when you want to be careful about wine's inherent aromas and flavors, vertical storage considering cork influence appears preferable.

Note that even closures other than cork, such as screw caps, have been confirmed to adsorb certain aromas. Therefore, we cannot say "screw caps can be stored any way."

Based on current verification results, it seems we can conclude that valuable wines, regardless of closure type, are recommended to be stored vertically in consistently cool, dark locations.