To obtain the materials which are capable of surely and homogeneously maintaining foam within dough by mixing a calcium chloride soln. with a silk fibroin soln. subjected to a ceresin removal treatment and melting the mixture by heating, then subjecting the mixture to cooling and dialyzing to form a dialyzed internal liquid from which the calcium chloride is removed, then subjecting the liquid again to the dialysis after adjusting its pH to acidity.

For example, the ceresin is removed from waste silk by iterating three times of the operations of boiling the waste silk for 30 minutes in a soln. of sodium hydrogencarbonate of 1% concn. and discarding the supernatant liquid thereof, then boiling the waste silk again by the same soln. Next, 500ml calcium chloride soln. is added to the soln. of 50% concn. on the basis of 20g silk fibroin from which the ceresin is removed and the soln. is heated for about 8 hours at about 95°C. The soln. is then subjected to the dialysis treatment for 3 days with the city water by using cellulose tubes for dialysis after the cooling. Acetic acid is added to the dialyzed internal liquid from which the calcium chloride is removed by the dialysis described above to adjust its pH to 2.8 and again the soln. is returned to the dialysis membranes and is subjected to the dialysis for 7 to 8 days, by which the desired material is obtd.