A soy protein product having a protein content of at least about 60 wt % (N×6.25) d.b., preferably a soy protein isolate having a protein content of at least about 90 wt % (N×6.25) d.b., is prepared from a soy protein source material by extraction of the soy protein source material with an aqueous calcium salt solution, preferably calcium chloride solution, to cause solubilization of soy protein from the protein source and to form an aqueous soy protein solution, separating the aqueous soy protein solution from residual soy protein source, concentrating the aqueous soy protein solution while maintaining the ionic strength substantially constant by using a selective membrane technique, optionally diafiltering the concentrated soy protein solution, diluting the concentrated and optionally diafiltered soy protein solution into water to cause the formation of a precipitate, acidifying the mixture of precipitate and diluting water to re-solubilize the precipitate and form a clear acidified soy protein solution, concentrating the clear acidified soy protein solution while maintaining the ionic strength substantially constant by using a selective membrane technique, optionally diafiltering the concentrated clear acidified soy protein solution, and drying the concentrated and optionally diafiltered clear acidified soy protein solution.