“Petit Verdot is a red-wine grape originating in the Bordeaux region of France (but see the “Factoid” below). Though traditionally used almost exclusively in small amounts in the traditional Bordeaux blends, it has acquired a second life in the New World, and is now often considered one of the dozen and a half or so of world-class red-wine grapes (those in boldface in the varietals lists up the the page). Its popularity with winemakers in its native region had declined severely owing to the vineyard difficulties it presents in that climate; but, in the much more beneficent climates of the New World, it is almost a diferent grape, coming to a late-season maturity that allows it to express itself in impressive monovarietal wines.
Varietal Petit Verdot is distinguished by a deep violet color (one U.S. Winery calls its PV “Inkblot”), high tannin levels and acidity, and a strong, rich flavor. That flavor is variously described as involving notes of dark fruit, cedar, tar, and spices (typical of Bordeaux varieties), as well as less typical overtones, such as (especially when young) banana and vanilla. It is often compared with Syrah for the sorts of wines it makes.
To be a success, a monovarietal bottling requires not only good grapes, but some care in the vinification: the high tannins typically want to be tamed a bit with some oak aging, but if such oaking is overdone, it can easily obscure the fruit and other inherent flavorings of the wines (a problem with oaking not limited to PV wines, but especially problematic here). But, to repeat, grapes grown in warm, long-season climates present distinctly fewer such problems, allowing substantially less oaking and decidedly more exciting wines.
Factoid: There is much speculation that PV was brought north to Bordeaux from an original warmer Mediterranean home by the Romans; that makes sense, as it seems unlikely that the grape developed in a climate so ill-suited to its growth as Bordeaux.” – That Useful Wine Site.com