Salted fermented shrimp

Jeotgal, seafood preserved in salt and left to ferment, is among the oldest Korean foods: the Samguk sagi lists it among Silla's royal betrothal gifts in the late 7th century. Saeujeot became especially widespread in the Joseon period, when small shrimp were plentiful. The Sejong sillok records salted shrimp sent as tribute to Ming China, and the 19th-century fisheries text Nanho eomokji describes boats carrying jars and salt to sea so the catch could be salted on board.

Saeujeot is made from small shrimp, or in some regions from tiny mysid shrimp (gonjaengi) or freshwater shrimp, and is named by the month of salting: ojeot (fifth month), yukjeot (sixth month), chujeot (autumn) and dongbaekhajeot (winter). The plump summer yukjeot is considered best for kimjang kimchi, while ojeot and chujeot suit everyday side dishes. In the shrimp's own enzymes, proteins slowly break down into amino acids, giving the paste its savory taste.

Ongampo in Gwangcheon (Hongseong, South Chungcheong) is famous for maturing saeujeot in about thirty earthen tunnels that stay at around 15–17 °C. In kimchi, saeujeot is the classic jeotgal of central and northern Korea, used in kimchi and kkakdugi, while southern provinces lean on anchovy. It also seasons stews (jjigae) and is the classic accompaniment to boiled pork.

• Savory without much fat: Fermentation breaks shrimp protein down into amino acids, adding umami; a recent study found that adding jeotgal to kimchi increased savory, amino-acid–derived flavor compounds.
• Minerals in small doses: The Encyclopedia of Korean Culture describes jeotgal as a traditional source of calcium in a diet with little dairy, and Korean data list calcium, iodine and vitamin B12 per 100 g — but servings are tiny.
• Very high in sodium: About 8 g of sodium per 100 g in Korean food-composition data; the FDA's daily value for sodium is less than 2,300 mg.
• Allergen: Contains crustacean shellfish, one of the nine major U.S. food allergens. Keep refrigerated once opened.