Merlot grapes have been traditionally used as blending grapes in their native France to add fruitiness and softness to rougher varietals like Cabernet Sauvignon. However, Merlot has more recently been "discovered" and successfully produced as a legitimate stand-alone wine, particularly in California.
Merlot is less forgiving of inattentive viticulture than Cabernet Sauvignon. Once ripe, it should be harvested fast because of its propensity to quickly over-ripen and thus lose its acidity, which tends to result in a dull wine. After a winemaker determines when to harvest (usually mid-September through early October), the grapes can be picked either by machine (mechanical harvesting) or by hand, subject to winery standards and rules.
Once harvested, the grapes are transported to the winery where they are de-stemmed and crushed prior to fermentation. As with all red wines, Merlot juice is fermented with the skins---this combination is called must. The fermentation process can take place in either wooden casks or tanks.
The winemaker may choose to ferment the must using the yeast naturally present in the air, or by selecting custom strands of yeast for the process, akin to using a proprietary formula for consistency of final product. The must is then subjected to alcoholic fermentation, the process where yeast converts sugar into alcohol. The length of fermentation depends on the winemaker, but for Merlot, it tends to range from 7 to 18 days.
One of he by-products of fermentation is heat---and the hotter the faster the conversion of sugar into alcohol occurs. Sometimes the winemaker chooses to cool the must before fermentation to give grapes some more skin-contact time for intensity of flavor.
The other by-product of fermentation is the release of carbon dioxide, which pushes up pulp and grape skins and forms a cap. This cap is frequently plunged down and "pumped over" to prevent drying out.
After alcoholic fermentation ends, most Merlot undergoes a second malolactic fermentation, which is the process of converting bitter malic acid (naturally present in grape must) into a softer lactic acid for fruitiness and softness of flavor. This can either be achieved naturally or by inducing certain lactic bacteria.
Aging and Bottling
The most common method for storing Merlot wine is in oak barrels or oak chips, which imbue the wine with flavor and its characteristic taste. Aging time for Merlot varies greatly, but it is usually somewhere between 6 and 18 months. After aging in oak, Merlot is bottled and sometimes kept for more aging in the bottle before release.
Merlot comes in a wide variety of styles and flavors, but it's generally considered to be a gentler, softer cousin to Cabernet Sauvignon. It's famous for ripe plum and cherry flavors combined with a characteristic softness and velvety texture.