Dried laver needs to be soaked in cold water. When eating laver, you need to soak it for about fifteen minutes, so that the laver can be fully soaked, because it contains a lot of sand. Porphyra can be eaten after cooking for about five minutes. If it is cooked for too long, there will be no toxin, but it will affect the taste. If the laver soaked in cold water is blue-purple, it means that the laver has been polluted by poison before drying and packaging, and this laver is harmful to human body and cannot be eaten.