Limes are the most acidic of the citrus fruits, as much as 8% of their weight coming from citric acid. The small, seedy Mexican or Key lime, C. aurantifolia, is the standard sour citrus fruit in the tropics, where lemons don’t grow well. In western Asia it’s sun-dried whole, then ground and used as an aromatic, somewhat musty acidifier. The larger, seedless, more cold-tolerant Persian or Tahiti or Bearss lime, C. latifolia, may be a hybrid between the true lime and lemon, and is more common in the United States and Europe. Despite the general impression that limes are characteristically “lime-green,” both turn pale yellow when fully ripe. They owe their distinctive limeness to pine, floral, and spicy aroma notes (from terpenes).