Identify a key wine from the Touraine region of the Loire Valley.

The correct answer is Vouvray, which is a significant wine-producing area located in the Touraine region of the Loire Valley. Vouvray is particularly renowned for its white wines made from the Chenin Blanc grape, which can produce a wide range of styles including dry, demi-sec, and sweet wines, as well as sparkling varieties. The unique terroir of Vouvray, characterized by its limestone soils and microclimates, contributes to the distinctive characteristics of the wines produced there, such as vibrant acidity and complex fruit flavors.

Coteaux du Layon is associated with sweet wines made mainly from Chenin Blanc as well but is primarily recognized as an appellation within the Anjou region rather than Touraine. Muscadet refers to wines typically made from the Melon de Bourgogne grape and is produced in the Pays Nantais, which is further west in the Loire Valley. Sancerre, while it is a well-known appellation renowned for Sauvignon Blanc, is situated in a different subregion of the Loire Valley, specifically the Upper Loire. Thus, Vouvray stands out as the key wine from the Touraine region in this context.