The Japanese term for ramen broth made from dried baby sardines is niboshi. Niboshi are small dried fish used to prepare dashi, the foundational soup stock of Japanese cooking. Although sardines are the most familiar source, niboshi can also refer to dried anchovies, round herring, sand lance, and related small fish.
To make niboshi dashi, cooks commonly soak the dried fish in water, sometimes removing the heads and entrails first to reduce bitterness. The liquid may be steeped overnight or heated gently until the fish’s savory flavor infuses the stock. In ramen, niboshi broth is valued for its concentrated seafood aroma and deep umami character.
A common mix-up is confusing niboshi with katsuobushi, which is made from dried and fermented skipjack tuna, or kombu, a type of kelp. In western Japan, the same dried-fish ingredient is often called iriko. Niboshi is also eaten as a snack and appears in tazukuri, a sweet-salty New Year dish.