Kagawa project turns udon noodle waste into premium sea urchins

Yushokuboya, a restaurant company based in Kagawa Prefecture, has launched “Sanuki Udon Uni” last month, a new sustainable food product that turns waste from Sanuki udon noodles into feed for farmed sea urchins.

The project is a collaboration with Tadotsu High School’s Marine Production Department, the Aji Fisheries Cooperative Association and local government bodies. It aims to solve two local issues: the depletion of seaweed beds, known as “isoyake,” in the Seto Inland Sea and the waste generated during the production of Kagawa’s famous udon noodles.

The isoyake phenomenon is caused by an overabundance of purple sea urchins (Murasaki Uni) that graze on seaweed, destroying vital habitats for fish and other marine life. In response, local fishers cull the urchins to protect the ecosystem. This project takes those culled urchins and repurposes them.

The idea originated in November 2023 from a conversation between Akihiro Hosokawa of Yushokuboya and Yoshiki Osaka, a teacher at Tadotsu High School. They proposed using surplus noodles and boiling water from udon production, which would otherwise be discarded, as a food source for the urchins. The project would be able to simultaneously address marine conservation and food waste, aiming for both seaweed bed regeneration and resource circulation.

Land-based aquaculture experiments began in April 2024 at the high school. Students took charge of feeding and managing the urchins, testing various diets before establishing a method of freezing the udon waste for use as feed. The Aji Fisheries Cooperative Association supplied the culled urchins for the trials.

In April 2025, Yushokuboya established the “Sanuki Udon Uni Labo®,” a research and development hub located near the high school to formalise quality standards and develop menus. The resulting sea urchin is described as having a white, creamy taste and growing faster than its wild, seaweed-fed counterparts. The project has already received recognition, winning an Encouragement Prize at the 2025 Grand Prize for the Global Environment Awards and the Kagawa Food Loss Reduction Grand Prize.

Yushokuboya will begin offering the Sanuki Udon Uni as a sashimi dish, limited to 10 servings per day, at its Marugame store. The company plans to expand its aquaculture facilities in summer 2026 to begin wholesale distribution within Kagawa Prefecture. A nationwide launch, with sales at Tokyo’s Toyosu Market and inclusion in the hometown tax donation programme, is planned for 2027.