Blended Wine
Unless the wine you're drinking is specifically named after a variety of grape—say Riesling, Chardonnay, Merlot, or Cabernet sauvignon, to list a few of the possibilities, it's probably a blended wine. All Bordeaux, for instance is a blend; so are Beaujolais, Chianti, and Rhone, not to mention most Champagne, Sherry and Port. Blends are carefully produced by the winery, using one of two basic methodologies; either attempting to keep the flavor as close as possible year to year, and thus essentially using the same percentages of various varietals, or, to produce the best possible wine given the vintages available in a given year. The blend is created before the final aging, and the particular choices in a blend are determined by taste, including nuances like tannin, and color.