Peel tamarinds of the peel, large seeds and strains. Soak overnight. Strain in a colander and press with your hands or a spoon. Place tamarind juice in a saucepan. Bring to a boil, add sugar, and simmer over medium heat for 40-45 minutes. Juice should have thickened considerably. Squeeze in the fresh lime juice, let it simmer for a couple more minutes and let it cool.