Is it still safe to eat tengusa (a type of seaweed) that has been soaked for a full day and night?

Under normal circumstances, whether agar can be consumed after soaking for one full day and night depends on the storage conditions. It is safe to eat if soaked in the refrigerator and shows no signs of spoilage, but it is not recommended if soaked at room temperature. The detailed analysis is as follows:

Agar is a common edible seaweed rich in dietary fiber and minerals. Soaking helps remove impurities and soften the texture. Refrigeration inhibits bacterial growth; if the soaking container is well-sealed and there are no signs of spoilage such as unpleasant odor or sliminess, the agar can be safely cooked after thorough washing, generally without causing adverse effects. However, soaking at room temperature for an entire day and night allows bacteria to multiply rapidly, increasing the risk of spoilage, which may lead to gastrointestinal discomfort if consumed. Therefore, agar soaked at room temperature should absolutely not be eaten.

Before consumption, carefully inspect the agar. If it exhibits increased slime, darkened color, or a sour or rotten smell, it should be discarded immediately. In daily life, it is advisable to control soaking time according to the amount needed, prepare it just before cooking, and develop good food handling habits to ensure food safety.