Optimal Wine Storage Humidity: Protecting Your Collection

Optimal wine storage humidity is crucial for your fine wine collection. It matters most for bottles sealed with natural corks. Humidity helps stop corks from drying out. A dry cork lets oxygen into the bottle. That grows the ullage space. In time the wine may spoil or oxidize (Australian Wine Research Institute (AWRI)). Too much humidity carries risks too. It can damage wine labels. That makes a bottle harder to name, and it can hurt resale value. High humidity also raises the risk of mildew on the outer surface of corks. Wine experts like Jancis Robinson note that 75% humidity is often cited as ideal. She also states there is "very little significant research to definitively establish an optimal range". Climate Controlled Wine Storage keeps humidity between 55% and 75%. For Champagne, the Comité Champagne recommends "high and constant" humidity "between 60% and 80%" (Comité Champagne).

Why is wine storage humidity important for your collection?

The right wine storage humidity protects your wine. It guards against physical damage and spoilage. For wines sealed with natural corks, humidity keeps the corks from drying out. If a cork dries out, oxygen can enter the bottle. It fills the ullage space. The wine may then spoil or oxidize. The AWRI notes that "leakage can occur if the air is too dry" for wines under natural closures. That oxygen ingress can change the wine's sensory properties. It can also cut its shelf life (AWRI).

Humidity that is too high also poses risks. It can damage wine labels. A damaged label makes the bottle harder to name. It can also hurt resale value. Chanut et al. (PNAS Nexus 2023) further note that a relative humidity "above 80% has been found to increase risk of mildew formation on the outer surface of cork." This balance is key to the wine's quality. It also shapes what the bottle will fetch, which matters if you are weighing how to sell fine wine. The link between humidity to cork saturation to ullage is what protects your investment.

What is the ideal humidity range for wine storage?

Experts still argue about the ideal humidity range for wine storage. Several published figures exist. Jancis Robinson notes that 75% humidity is often cited as ideal. She also states that "there is very little significant research to definitively establish an optimal range". Climate Controlled Wine Storage facilities keep humidity between 55% and 75%. That range avoids air that is too dry or too moist. It also aids wine development.

For Champagne, the Comité Champagne recommends that humidity "must be high and constant, between 60% and 80" (Comité Champagne). Chanut et al. (PNAS Nexus 2023) state that "relative humidity above 50% is required for good elasticity of cork-based closures." The same team cautions that "a relative humidity above 80% has been found to increase risk of mildew formation on the outer surface of cork."

Note one outlier. Amon and Simpson (1986) recommend storing bottled wine with the cork in contact with the wine in a "cool (15-20°C), dry location" (AWRI; AWRI Technical Note TN09). That call for a "dry location" cuts against the wider view. Most sources want some humidity to stop cork drying. If you are building a cellar for fine wine investment, weigh these views with care.

Does bottle orientation affect cork moisture and oxygen ingress?

Studies have looked at bottle orientation, cork moisture and oxygen ingress. Their results differ. Most wine racks are built for horizontal storage. The idea is simple: keeping the cork in constant contact with the wine stops it drying out.

Research by Mas et al. (2002) found that "oxidation was higher for upright samples sealed with agglomerated cork stoppers" in white wine samples. That held from the 3-month timepoint onwards (AWRI). Skouroumounis et al. (2005) studied wooded Chardonnay and Riesling wines over a 60-month period. They concluded that bottle orientation "little effect on the chemical composition and sensory properties" of the two wines (AWRI).

Chanut et al. (PNAS Nexus 2023) ran a systematic study. It used miniaturized bottle systems with 6-mm-thick microagglomerated cork wafers and model wine. The team tested two storage positions. One was "vertical storage" (cork in contact with vapor phase). The other was "horizontal storage" (cork in contact with liquid phase). Position "did not modify the oxygen transfer" through the bottleneck-cork system over a 24-month aging period at 20°C. This study also noted that the "oxygen diffusion coefficient of the cork wafer alone was not modified, whatever the storage conditions," including storage position.

For Champagne, the Comité Champagne states that bottles "can be stored upright or on their sides" (Comité Champagne). It also recommends storing Champagne "on its side in a cool, dark, draft-free place" with "generous humidity" (Comité Champagne). So upright storage is allowed. Horizontal storage is still what the official body advises. For more on fill levels and condition, see our guide to wine ullage levels.

How do temperature and humidity interact in wine storage?

Temperature and humidity are closely linked in wine storage. Both bear on cork integrity and oxygen transfer. The AWRI recommends storing bottled wine under insulated or temperature-controlled conditions that "minimise fluctuations in both temperature and humidity" (AWRI Technical Note TN09). Avoid thermal cycling, where temperature varies a lot. It can lead to "Leakage of wine and/or movement of cork stoppers due to thermal expansion of wine" (AWRI).

The Chanut et al. (PNAS Nexus 2023) study used microagglomerated cork wafers in miniaturized bottle systems with model wine. It sets out what temperature does to oxygen transfer:

• 20°C: At this temperature, the oxygen barrier properties of the bottleneck-cork system "remained unchanged over 24 months of aging."
• 35°C: This temperature, "easily reached during bottle shipping," did not significantly increase total oxygen transfer for up to 9 months. However, "beyond this duration of storage, a significant transfer at the glass-cork interface started to occur."
• 50°C: At this higher temperature, a "tremendous oxygen transfer occurring at the glass-cork interface was noticeable, even from 3 months." This phenomenon was "further accentuated after 6 months." It then approached the diffusion coefficient of oxygen in the air. That indicated "the presence of leakage at the glass-cork interface."

The study blames the extra oxygen transfer at higher temperatures on two things. One is a "partial melting of the surface treatment agent" on the cork stopper. That agent is made of paraffin and silicone. The other is a "modification of the mechanical properties of the cork" (Chanut et al., PNAS Nexus 2023). Cork hydration can also shape oxygen transfer at the glass-cork interface. It changes the cork's mechanical properties (Chanut et al., PNAS Nexus 2023).

These findings show a split. The oxygen diffusion of the cork material itself may stay stable. The glass-cork interface is the weak point, and heat is what breaks it. That joint carries a large share of total oxygen transfer. Heat can then harm the long-term keeping of your fine wines. That shows up in their value on the live fine wine market index.

What about alternative wine closures?

Natural corks are the traditional choice. Other wine closures are now common too. They include synthetic stoppers, glass stoppers, and screw caps. For these closures, worries about humidity and oxidation are "not as pronounced" as with natural corks.

The "relatively recent popularity and increased usage of these closures have not given many opportunities for research into the storage and ageing potential of wines that use these closures". So you may worry less about cork drying out with a screw cap. Other factors still matter. Temperature and light sensitivity count for all wines, whatever the closure. For more on securing your collection, explore our storage pillar.

Knowing the best storage conditions is one part of running a collection well. To get the most from your cellar, you also need precise timing.