A winery that claims to use American oak is referring to the type of barrel used during the aging process. Wines were traditionally aged in French oak barrels, but American oak—that is, oak grown in the United States—has become increasingly popular worldwide for both its price ($250 to $300 per barrel, as opposed to $600 for a French barrel) and the overt vanilla and dill flavors it imparts. Some grape varietals such as Shiraz, Zinfandel, and Tempranillo have a natural affinity for maturation in American oak. Certain wine regions outside the U.S. such as Spain's Rioja and most of Australia—have created a style of wine dependent on American oak flavors. Occasionally a French vintner will use American oak barrels, but this is a rarity.