Heavy Toast brings pronounced caramelized, carbonized and toast flavors very quickly - it doesn't need much contact time. It is most often used in big, bold red wines.
Medium Plus Toast
Medium Plus Toast is between Medium and Heavy Toast. It has aromas of honey, roasted nuts and a hint of coffee and spices. It seems to be the ideal toast level for red wines.
Medium Toast has less tannins but more bouquet, so will impart more aroma than flavor. It has a warm, sweet character with strong vanilla overtones.
Light Toast fresh oak, coconut and fruit flavors.
French oak tends to be mellower than American which is more pronounced.