Cooking wine or Cooking sherry refers to inexpensive grape wine or rice wine (in Chinese and other East Asian cuisine). It is intended for use as an ingredient in food rather than as a beverage. Cooking wine typically available in North America is treated with salt as a preservative and food colouring. When a wine bottle is opened and the wine is exposed to oxygen, a fermentative process will transform the alcohol into acetic acid resulting in wine vinegar. The salt in cooking wine inhibits the growth of the acetic acid producing microorganisms. This preservation is important because a bottle of cooking wine may be opened and used occasionally over a long period of time.
Cooking wines are convenient for cooks who use wine as an ingredient for cooking only rarely. However, they are not widely used by professional chefs, as they believe the added preservative significantly lowers the quality of the wine and resultantly the food made with that wine.
Most professional chefs prefer to use inexpensive but drinkable wine for cooking, and this recommendation is given in many professional cooking textbooks as well as general cookbooks.
Many chefs believe there is no excuse for using a low quality cooking wine for cooking when there are quality drinkable wines available at very low prices.
Cooking wine is considered a wine of such poor quality, that it is unpalatable by itself and intended for use only in cooking. (There is a school of thought that advises against cooking with any wine one would find unacceptable to drink; however, a recent study has found that inexpensive wine works as well as expensive wine in cooking.)
See also: www.d-i-wine.com, www.infozeek.net