Bún riêu cua is served with tomato broth and topped with crab or shrimp paste. In this dish, various freshwater paddy crabs are used, including the brown paddy crab found in rice paddies in Vietnam. The crabs are cleaned by being placed in clean water to remove dirt and sand. The crabs are pounded with the shell on into a fine paste. This paste is strained and the crab liquid is a base for the soup along with tomato. The crab residue is used as the basis for crab cakes. Other ingredients for this dish include tamarind paste, fried tofu, mẻ or giấm bổng (kinds of rice vinegar), Garcinia multiflora Champ., annatto seeds (hạt điều màu) to redden the broth, huyết (congealed pig's blood), split water spinach stems, shredded banana flower, rau kinh giới (Elsholtzia ciliata), spearmint, perilla, bean sprouts and chả chay (vegetarian sausage). This dish is rich in nutrition: calcium from the ground crab shells, iron from the congealed pig's blood, and vitamins and fiber from the vegetables.
^Aruna Thaker, Arlene Barton Multicultural Handbook of Food, Nutrition and Dietetics 2012 Page 171 "Bún riêu: Noodle soup .."
^Vietweek May 18th 2012 print edition The market beyond the hedge "Not surprisingly, seasoned shoppers at Phung Hung delight in the fermented fiat of a soup so pungent, it makes bún riêu seem like a Cup-o-Noodles. Bún mắm allegedly came from the Mekong Delta province of Soc Trang, where Khmer, Chinese and Vietnamese communities have intermingled for centuries."