Rice Paddy Crab
[Rice Field Crab, Black Crab; Boo Kem, Bpoo Kem (Thai, salted); Ba Khía Nguyén Con (Vietnam, salted); Somanniathelphusa sp.]
Rice paddies across Southeast Asia are often infested with these small freshwater crabs. They are considered pests as they eat young rice plants. They are hard to get rid of, because, when the paddies dry out, they tunnel into the mud and hibernate until the water comes back. Nonetheless, they are also an important commercial product, sold salt fermented whole, or ground into black crab paste. Both forms are used in Laos, Issan (northeastern Thailand) Vietnam and Cambodia, but unsalted crabs are also used, often fried whole, or ground up live for Bun Reiu Soup. The photo specimen (salted) was 1.7 inches across the carapace and weighed 1-7/8 ounces.
Mangrove crabs, about the same size, are an alternative, and will be free of parisites that are sometimes found in Paddy Crabs, but they are only available along the mangrove coasts.
More on Crabs.
These whole salted crabs and crab paste made from them are used in the famous Green Papaya Salad of Laos and Issan (northeast Thailand).
In Vietnam, fresh crabs are pounded to paste and strained, using the juice in a popular soup called Bún Rieu Cua. The crab juice is combined with pig blood, tamarind, rice vinegar, vegetables, seasonings and other ingredients. The residue is used to make crab cakes, which may also be used in the soup.
Buying: Whole salted Black Crabs can be found in the frozen food cases of some markets here in Los Angeles. The photo specimen was purchased from the San Gabriel Superstore in San Gabriel in a 14 ounce tray priced at 2017 US $3.56 / pound. The store also had 14 ounce tubs of the crabs chopped up for $3.41 / pound.
Cooking: One Thai source says his mother always boiled salt fermented crabs before using them in Som Tum salads to assure any parasites were killed. This also reduced the saltiness a little, but does not damage the flavor. For salads and the like, the top shell is pried off and discarded along with the gills under it. For pastes, sauces and Bun reiu soup, the whole crab is ground up.
Paddy Crab Pastes & Sauces For instructions on making some Paddy Crab Pastes and Sauces, and more detail on commercial products, see our Crab Paste / Sauce page.
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