Humidity
Of all the conditions essential for optimum storage of your
fine wine, humidity is one of the most important to be mindful of.
The structure of your wine is completely
dependent on the environment you provide it with. Unfortunately,
humidity is also the most difficult element to control.
Proper humidity is essential in keeping the wine's cork moist,
preventing the wine from evaporating to a damaging degree whilst in
storage. However, corks do not completely seal a bottle of wine, so
almost all bottles laid down for extended periods lose some of
their contents due to evaporation. If the air is too dry,
evaporation speeds up, reducing the level of your wine and
increasing the ullage, or the gap between the bottom of the cork
and the wine. When ullage increases significantly, it automatically
decreases the value of your wine. A look at Sotheby's sales guide
clearly demonstrates how important ullage is in determining the
value of a wine. Over time in less than perfect wine storage
conditions, low humidity can also cause the cork to dry up to such
an extent that it loses its elasticity and lets air into the bottle
- ruining wine through oxidation.

The ideal humidity level for wine storage is 70 to 80%. When
stored in optimum conditions, fine wine can be laid down for 10 to
30 years and, according to wine experts, even as long as 50 years.
This is why wine has traditionally been stored underground, natural
humidity levels allowing for more cost effective and predictable
control over the optimum storage conditions. To attempt to maintain
the correct humidity level for wine storage anywhere above the
ground, for the entire length of that period, is virtually
impossible.
Lack of humidity is not only one of the biggest problems, but
also the most difficult to solve. Ambient humidity in the UK
fluctuates between 57 to 88% across a typical year. To artificially
humidify the air might help the wine, but is considered
commercially unviable by wine storage providers. Excessive humidity
in storage can also cause a bottle's labels and packaging to
discolour and deteriorate. This affects the presentation of the
wine and, in today's market, would definitely decrease its
investment value.