Tamarind juice is made from block tamarind concentrate sold in Asian stores, some supermarkets and by mail order. To make tamarind juice, break off a piece of the block and soak in warm water for 10 to 15 minutes. Squeeze and loosen the remainder of the flesh from the seeds and strain. Use a ratio of approximately 1:4 tamarind concentrate to water.
Source : sallys-place.com