Tamarind is a vital ingredient in Thai cooking. There are two types of Tamarinds—sour tamarind and sweet tamarind (known as Markham Wan around Thailand). They both look the same with curved pod-like shape but have a different taste. You can find these fruits on tamarind trees which grow up to 15-25 meters. When Tamarind has matured, the brown shell becomes very thin, and it's easy to separate it from the flesh.
Usually, sour tamarinds are used for producing chilly sauce and spicy soups. Pad thai (stir-fried rice noodle) is a very famous Thai street food which includes tamarind sauce. Sweet tamarind is very tasty in dried form, and you can also try ripe tamarinds directly from the tree. Sour tamarinds grow all around the Thailand while sweet ones are much harder to find. They are harvested in just in a few Thai provinces, the most popular are Phetchabun and Loei.
Tamarind harvest season lasts from November until February. While visiting Thailand at that time, don't miss an opportunity to try fresh tamarinds. Also, during winter, Phetchabun and Loei provinces hold harvest festivals with different entertainments and exhibitions.