Puglia, the heel of Italy, produces more olive oil than any other Italian region, from groves that include some of the oldest, most monumental olive trees in the world. The northern province is Coratina country — one of the most intensely bitter, pungent and polyphenol-rich oils made anywhere — while the south leans softer and fruitier. The region's ancient ulivi secolari have been threatened by the Xylella bacterium, making its heritage groves a focus of conservation.