This syrup is tart, sweet, and makes a great addition to cocktails, punches, or lemonade. Or, try some whisked into barbecue sauce or glaze.
Peel lemon; reserve peels. Squeeze juice from lemon to equal 3 tablespoons. Peel grapefruit; reserve peels. Reserve grapefruit flesh for another use.
Combine sugar, tamarind puree, lemon juice, lemon peels, and grapefruit peels in a medium saucepan. Bring to a simmer over medium, and cook, whisking constantly, until sugar is dissolved, about 2 minutes. Remove from heat, and let cool completely before using, about 30 minutes.
Tamarind syrup may be stored in an airtight container in refrigerator up to 1 week.