Sea urchins are not bitter, and if they have a bitter taste, the main reason is that merchants add too much alum or use mature female sea urchins in order to keep them fresh. Alum is a common food additive used to maintain the color and texture of sea urchins, but overuse can lead to a bitter taste. Mature female sea urchins produce more bitter substances during the breeding season. If the sea urchin tastes a little bitter, it is recommended to choose a reputable merchant to buy it and try to avoid adding too much alum or choose immature male sea urchins for better taste and texture.