Bún riêu is the Vietnamese soup that combines crab, tomatoes and rice vermicelli in a reddish broth.
Traditional bún riêu is associated with northern Vietnam and uses freshwater crab, whose pounded meat and shell contribute flavor and help form floating crab-paste pieces. Tomatoes add acidity and the characteristic reddish color. The soup is served with thin rice vermicelli and may include tofu, pork, snails or other regional additions.
The phrase riêu refers to the savory crab mixture that cooks into soft curds or cakes in the broth. Modern versions can use packaged crab paste or other seafood, so bowls vary widely while retaining the tomato-and-vermicelli identity.
Bún riêu is not the same as bún bò Huế. Both are noodle soups, but bún riêu is defined by crab and tomato, whereas bún bò Huế is centered on a beef-based, lemongrass-seasoned broth. Fresh herbs and lime are common accompaniments.