Kokum

Kokum is a fruit related to the mangosteen, and it is native to India. The dried fruit is used as a wonderfully fruity souring agent, and it works particularly well with pulses and vegetable curries.
Just drop a piece into the curry during cooking and let it infuse, resulting in a tartness that matches really well with the other spices in the dish.
It also works brilliantly in fish curries, when its sweet/sour nature comes into its own. Due to its sour taste, kokum can be used as an alternative to tamarind. Our wonderful Kokum is available in the form of dried slices.