Kokum is the dried, leathery rind of the fruit of Garcinia indica, an evergreen tree of India's tropical Western Ghats. Sun-cured to a glossy purple-black, the curled rinds are a tart, fruity souring agent — the coastal-Konkani counterpart to tamarind — adding a clean, slightly astringent acidity to curries, dals and the cooling summer drink sol kadhi.