Relative humidity in a wine cellar must be between 50% and 80%. In case the humidity level drops below 50%, the cork will dry out and decrease in volume causing the wine to escape and evaporate . Air will then invade its space, causing an uncontrolled oxidation process. Wine bottles should not be stored vertically, so that the wine keeps the cork moist by contact. Humidity level above 80% will most likely harm the labels, not necessarily the wine itself.
Temperature on the other hand is a more delicate issue. Authorities all over world confirm that the wine should be preserved at a constant temperature set between 10 - 16˚ C. At temperatures below 10˚ C, the necessary chemical reactions for the aging of wine decelerate, even cease. Although the wine does not degenerate at temperatures between 17 - 20˚ C, it matures too quickly, not being able to reach its full potential. Above 20˚ C the wine degenerates. Therefore, any chosen temperature between 12 - 14˚ C is accepted to be the ideal storage temperature.
However, in terms of wine preservation, avoiding fluctuations in temperature is more important than a certain temperature value itself. When the temperature rises, expanding wine inside a wine bottle increases the pressure and eventually escapes and evaporates around the cork. When the temperature drops again, the process is reversed and this time contracting wine creates a vacuum inside the bottles and sucks the air inside. By every incident of this nature, the amount oxygen inside the wine bottle increases and eventually oxidation (degeneration) of wine occurs.