or fluctuations in temperature and humidity. When properly stored, wines can maintain their quality and in some cases improve in aroma, flavor, and complexity as they age. Some wine experts contend that the optimal temperature for aging wine is , others . Wine refrigerators offer a smaller alternative to wine cellars and are available in capacities ranging from small, 16-bottle units to furniture-quality pieces that can contain 500 bottles. Wine refrigerators are not ideal for aging, but rather serve to chill wine to the proper temperature for drinking. These refrigerators keep the humidity low (usually under 50%), below the optimal humidity of 50% to 70%. Lower humidity levels can dry out corks over time, allowing oxygen to enter the bottle, which reduces the wine's quality through oxidation. While some types of alcohol are sometimes stored in the freezer, such as vodka, it is not possible to safely freeze wine in the bottle, as there is insufficient room for it to expand as it freezes and the bottle will usually crack. Certain shapes of bottle may allow the cork to be pushed out by the ice, but if the bottle is frozen on its side, the wine in the narrower neck will invariably freeze first, preventing this. Professions There are a large number of occupations and professions that are part of the wine industry, ranging from the individuals who grow the grapes, prepare the wine, bottle it, sell it, assess it, market it and finally make recommendations to clients and serve the wine. See also Outline of wine Glossary of wine terms Classification of wine Winemaking List of grape varieties Health effects of wine Storage of wine Maceration (wine) Pressing (wine) Vidal blanc Hybrid grape References Further reading online review External links The Guardian & Observer Guide to Wine Alcoholic drinks Ceremonial food and drink Cooking Fermented drinks Grape