Fish-head soup

What it is

Fish-head soup (魚頭湯) at a Tainan seafood restaurant is a big, gelatinous fish head cooked in one pot with mixed seafood. The local version adds xiguamian (西瓜綿), slices of baby watermelon salted and fermented as a pickle. It makes the broth slightly sour with a sweet aftertaste.

Where it came from

The soup fits Tainan's long habit of souring fish broth with pickled fruit. Supertaste, a food magazine, says the earliest recorded sour fish soups (酸魚湯) took their tang from salted, fermented green mango (鹹檨仔青). In his General History of Taiwan (臺灣通史), published under Japanese rule, the Tainan-born historian Lian Heng (連橫) wrote that unripe mango, peeled and salted, could be cooked with fresh fish for a pleasant sourness, and that only Tainan people knew the taste.

Salted watermelon comes from the same farm thrift. Around Lunar New Year, growers thin their crops, cutting away surplus young fruit so the rest can grow large. Rather than waste the culls, households pickled them, and xiguamian became a seasonal ingredient of the Chiayi and Tainan plain. Tainan cooks now use it in milkfish soup as well as in seafood soups.

How it is made

For the pickle, baby watermelons are peeled, halved or cut into chunks and rubbed with salt. They are packed into a container under a weight to draw out water, turned after three or four days, and left for about a week until they ferment and turn pale yellow. For the soup, the pickle is sliced thin and simmered with the fish head and seafood.

How to eat it

It is the shared soup of a seafood restaurant meal, ordered alongside crab, fried fish and stir-fries. Look for 西瓜綿魚頭湯 or 西瓜綿海鮮魚頭湯 on the menu.