Other than these components, it is also possible to add one or more proteins, such as egg white, casein, vegetable proteins and collagen, if desired. Their amount ranges from 1 to 10%, preferably from 1 to 5%, and the texture and the taste of the product can be improved by addition of these components. In any case, the mixture is mixed with addition of water at room temperature and left to stand for 1 to 2 hours to cause the materials to become swollen with water.