PURPOSE: To separate a fraction composed mainly of αs-casein and β-casein into a fraction composed mainly of αs-casein and a fraction composed mainly of β- casein, by cooling the original fraction at a specific temperature, and adding a bivalent salt thereto.

CONSTITUTION: A casein fraction composed mainly of αs-casein and β-casein and obtained by the fractional elimination of the fraction composed mainly of κ- casein from whole casein, is cooled at 0W10°C and added with 5W30m-mol of a bivalent salt (e.g CaCl2) to precipitate the fraction composed mainly of αs- casein. The fraction composed mainly of β-casein obtained as the supernatant liquid is separated from the above fraction by the solid-liquid separation. Sodium citrate or a chelating agent is added to each fraction, or the fraction is pH- adjusted, desalted by dialysis, ultrafiltration, etc. and dried.