Another sour fishy soup that is popular in southern Thai cuisine is Tom Sum Pla. Prepare with fresh salmon. Overall, it’s not quite as fiery as Gaeng Som, but it might just be one of the sourest soups that Thailand has to offer. Every spoonful is a tongue smack of acidity that results in an outward frown, but internal delight. Along with the delightful sourness, the soup is a fusion of turmeric root, shredded ginger and tamarind juice.