American oak, with flavors of vanilla, toasted coconut, caramel, honey, and coffee, has a more intense flavor than French oak. American oak has a lower level of tannin contribution than French oak so it does not add as much to the body and mouth feel of the wine. The darker the toast level the lower the tannin level will be.
French oak, with flavors of spice, vanilla, caramel, tea, toffee, and chocolate, has a more subtle flavor component than American oak. French oak has a much higher tannin content than American oak, adding complexity and structure to the body and mouth feel of the finished wine.
The toast level will effect the natural character of the oak from each origin. To achieve your final oak flavor and character goals it may be beneficial to blend different oak types and toasts.
Light Toast contributes fresh oak, coconut and fruit flavors, and higher levels of tannin.
Medium Toast has less tannins but more bouquet, so it will impart more aroma than flavor. It has a warm, sweet caramel character with strong vanilla overtones.
Medium Plus Toast is between Medium and Heavy Toast. It has aromas of honey, roasted nuts and a hint of coffee and spices.
Heavy Toast brings pronounced caramelized, carbonized, smokey, and toast flavors very quickly.