This article is from the WineMaking FAQ, by malak@CAM.ORG (Don Buchan) with numerous contributions by others.
Some debate exists about proper humidity levels required in storage.
Excessively humid conditions may bring about problems with mouldiness
on the corks and help to deteriorate the label, while excessive dryness
may lead to a dry, rotten cork. Whether or not humidity actually
affects the wine may be dubious.
Temperature of the storage area is important, however. Wines are more
susceptible to oxidation above temperatures of 75F (24C); they are also
adversely affected by conditions in which the temperature fluctuates
quickly over time.
Bottles should be kept on their sides to keep the cork moistened; by
drying out the corks may become more susceptible to leakage and allow
for the incursion of too much oxygen that may spoil the wine, as well
as, in very extreme situations, allow for some wine loss (and as such
oxygen incursion into the bottle) through evaporation.
The advice of keeping the labels up is primarily useful for identifying
the kind of wine you have in a given bottle -- ie the upwards-facing
label is easier to read. Also, if there is sediment in your bottles,
you can carefully handle the bottle such as to avoid mixing it into
Keeping your wine in a north facing room against the north wall (or
south in the southern hemisphere) generally is a myth. It is useful if
your southern-exposed room becomes excessively warm from the sun (see
above regarding storage temperature).
Light may also contribute to the premature ageing and deterioration of
the wine, and prolonged direct sunlight may cause undue temperature
For your convenience, your labels should also either clearly indicate
the wine type, its age, and any other information you decide is
relevant, or at least an identification code which is clearly explained
in a handy log book.