Methods of producing arginine bicarbonate solutions in very high concentrations including reacting an arginine slurry containing a first portion of arginine with a source of carbon dioxide gas at elevated pressure and temperature, adding subsequent portions of arginine to the resulting solution and further reacting with compressed carbon dioxide until a final solution containing in excess of 50% by weight are provided which include preparing an arginine solution by subjecting an arginine water slurry to elevated pressure and temperature and reacting the arginine solution with a source of carbon dioxide gas to form a solution comprising arginine and bicarbonate anion and recovering arginine bicarbonate from the solution.