The Loire river has a significant effect on the mesoclimate of the region, adding the necessary extra few degrees of temperature that allows grapes to grow when the areas to the north and south of the Loire Valley have shown to be unfavorable to viticulture. In addition to finding vineyards along the Loire, several of the river's tributaries are also well planted-including the Allier, Cher, Indre, Loir, Sèvre Nantaise and Vienne Rivers. The area has a continental climate that is influenced heavily by the Loire River and the Atlantic ocean at the western edge of the region. The climate can be very cool with spring time frost being a potential hazard for the vines. During the harvest months rain can cause the grapes to be harvested under ripe but can also aid in the development of Botrytis cinerea for the region's dessert wines.
With over 185,000 acres (750 km2) planted under vine, the Loire Valley is about two-thirds the size of the Bordeaux wine region. Due to its location and marginal climate, the overall quality of a vintage has a dramatic effect on the quality of the region's wines-more so than with other French wine regions. The most common hazard is that the cool climate will prevent the grapes from ripening fully and developing the sugars needed to balance the naturally high acidity of the grapes. During these cool vintages the Sauvignon blanc based wines are lighter in color, less fruity and have more pronounced mineral notes. The Cabernet franc based wines are also lighter in color with more vegetal or "weed"-like aromas. In riper vintages, a Loire Cabernet franc will develop aromas of raspberries and lead pencil shavings.
Winemaking in the Loire is characterized by a general avoidance of barrel aging and malolactic fermentation. However some winemakers have begun experimenting with both. Chaptalization is permitted here and can help wine makers compensate for the under ripeness of the grapes in some years. For red wines there has been more emphasis on extending the maceration time of skin contact in order to bring out more color and tannins into the wine. Temperature control is also an important consideration with the cold autumn weather sometimes requiring that the must be heated in order to complete fermentation fully.
The Loire Valley is often divided into three sections. The Upper Loire includes the Sauvignon blanc dominated areas of Sancerre and Pouilly-Fumé. The Middle Loire is dominated by more Chenin blanc and Cabernet franc wines found in the regions around Touraine, Saumur, Chinon and Vouvray. The Lower Loire that leads to the mouth of the river's entrance to the Atlantic goes through the Muscadet region which is dominated by wines of the Melon de Bourgogne grape. Spread out across the Loire Valley are 87 appellation under the AOC, VDQS and Vin de Pays systems. There are two generic designation that can be used across the whole of the Loire Valley. The Crémant de Loire which refers to any sparkling wine made according to the traditional method of Champagne.