Black tea is the most common type of tea available worldwide. It has a broad range of flavors, but is typically heartier and more assertive than green or oolong teas. It is made by fully fermenting the harvested leaves (for several hours) before the heating or drying processes occur. This oxidation imparts a dark coloring and can increase the caffeine level. Black teas may range from blended and flavored teabags to handmade, artisan, loose-leaf teas.