Dissolve the dry ingredients in the water and milk, pasteurize and homogenize at 75'C (167'F) and 70 kg/cm^2 (1000 psi). Cool down by means of a heat exchanger to 5'C (41'F). Mix in the citric acid solution, flavor, and color (if any). Pass through continuous freezer adjusting outlet temperature to-6'C (21'F). Store at- 20 to -30'C (-4 to - 22'F).