A wine cellar is a storage area for wine in barrels or bottles and is normally built underground. It is a necessity in a quality wine cellar to provide a favorable environment to ensure that the wines kept there remain in a fresh state even after many years cellaring. This means that the temperature and humidity of the cellar have to be regulated at levels that will allow the wines to age slowly and develop complexity.
If a cellar is built above the ground, it could better be described as a wine room and if it contains less than 500 bottles and is above ground, it could be identified as a wine closet. The main purpose of building a wine cellar is to protect the wine from environmental factors that will compromise the quality of the wine. Factors such as light, high temperature or low humidity will all affect the wine in an adverse way. Wine is a living thing that must be protected from fluctuating temperatures, heat and light as well as vibrations. With proper storage, wine not only maintains its freshness but also improves the quality of its aroma, complexity and flavor.
Therefore, a quality cellar should not only maintain the vibrancy of the wine but also improve it. The right temperature in a cellar should range from 13 to 18 degrees C and it should be free from vibration. If the temperatures change from season to season, it should vary by less than 10 degrees C. For centuries, the French have stored their wines in underground caves at these temperatures and that is how people gauge the level of temperature for wine storage. To ensure that the final product has qualities of a well matured wine, the temperatures should not be higher than 18 degrees C as the wine will mature too fast. Wines that mature too fast will often taste more like vinegar and not have the refined and delightful flavor of a fine wine.
Active or passive describe the cooling system used in the wine cellar. A wine cellar with an active cooling system requires insulation and a vapor barrier installed. A special wine cooling unit is then installed in the wall to ensure that the temperature and humidity are maintained at the correct levels. Many above ground cellars will require a cooling unit to maintain a constant temperature. Geographic areas that are naturally very cool are often suitable for a passively cooled wine cellar. Most underground cellars are passively cooled and frequently a well-constructed and well-insulated basement cellar can be passively cooled. A passive wine cellar requires no energy to operate. They are therefore cheaper to build and run albeit sometime unreliable in extreme weather.