A fermentation method for obtaining Neisseria meningitidis serogroup A capsular polysaccharide comprising: a) inoculating Neisseria meningitidis A into a fermentation medium having a pH between 7 and 7.5 and comprising: Dextrose from 8 g/L to 10 g/L, Sodium Chloride from 5.6 g/L to 6 g/L, Di potassium Sulphate from 0.8 g/L to 1 g/L, Arginine from 0.2 g/L to 0.4 g/L, Serine from 0.4 g/L to 0.6 g/L, Cysteine from 0.20 g/L to 0.25 g/L, Magnesium Chloride (MgCl2) from 0.18 g/L to 0.20 g/L, Calcium Chloride (CaCl2)from 0.020 g/L to 0.022 g/L, Ferrous Sulphate (FeSO 4 ) at 0.002 g/L, L-Glutamic Acid from 4.8 g/L to 5.2 g/L, Soya peptone from 8.8 g/L to 9.2 g/L, Ammonium Chloride (NH4Cl) from 0.44 g/L to 0.46 g/L, Di-potassium Hydrogen Phosphate (K2HPO4) from 3.8 g/L to 4.2 g/L and Yeast Extract from 5.30 g/L to 5.35 g/L; b) adding, from log phase onwards, a feed solution comprising: Dextrose from 70 g/L to 75 g/L, Mono sodium Glutamate from 37 g/L to 37.5 g/L, Arginine from 2.8 g/L to 3.2 g/L, Serine from 2.8 g/L to 3.2 g/L, Magnesium Chloride (MgCl2) from 1.8 g/L to 2.2 g/L, Calcium Chloride (CaCl2) from 0.13 g/L to 0.15 g/L, Ferrous Sulphate (FeSO 4 ) at 0.02 g/L, Soya peptone from 4.8 g/L to 5.2 g/L, Cysteine from 1.8 g/L to 2.2 g/L and Yeast Extract from 8.2 g/L to 8.4 g/L; c) adding an antifoam agent which is a alkoxylated fatty acid ester on vegetable base as a 10% v/v to 20% v/v solution, starting at 4 hour of fermentation till 11 hour, wherein final concentration of Struktol J673A® in fermenter is comprised between 0.01% and 0.1% v/v; d) harvesting and collecting 2 g/L to 2.5 g/L of Neisseria meningitidis A capsular polysaccharide. a) inoculating Neisseria meningitidis A into a fermentation medium having a pH between 7 and 7.5 and comprising: Dextrose from 8 g/L to 10 g/L, Sodium Chloride from 5.6 g/L to 6 g/L, Di potassium Sulphate from 0.8 g/L to 1 g/L, Arginine from 0.2 g/L to 0.4 g/L, Serine from 0.4 g/L to 0.6 g/L, Cysteine from 0.20 g/L to 0.25 g/L, Magnesium Chloride (MgCl2) from 0.18 g/L to 0.20 g/L, Calcium Chloride (CaCl2)from 0.020 g/L to 0.022 g/L, Ferrous Sulphate (FeSO 4 ) at 0.002 g/L, L-Glutamic Acid from 4.8 g/L to 5.2 g/L, Soya peptone from 8.8 g/L to 9.2 g/L, Ammonium Chloride (NH4Cl) from 0.44 g/L to 0.46 g/L, Di-potassium Hydrogen Phosphate (K2HPO4) from 3.8 g/L to 4.2 g/L and Yeast Extract from 5.30 g/L to 5.35 g/L; b) adding, from log phase onwards, a feed solution comprising: Dextrose from 70 g/L to 75 g/L, Mono sodium Glutamate from 37 g/L to 37.5 g/L, Arginine from 2.8 g/L to 3.2 g/L, Serine from 2.8 g/L to 3.2 g/L, Magnesium Chloride (MgCl2) from 1.8 g/L to 2.2 g/L, Calcium Chloride (CaCl2) from 0.13 g/L to 0.15 g/L, Ferrous Sulphate (FeSO 4 ) at 0.02 g/L, Soya peptone from 4.8 g/L to 5.2 g/L, Cysteine from 1.8 g/L to 2.2 g/L and Yeast Extract from 8.2 g/L to 8.4 g/L; c) adding an antifoam agent which is a alkoxylated fatty acid ester on vegetable base as a 10% v/v to 20% v/v solution, starting at 4 hour of fermentation till 11 hour, wherein final concentration of Struktol J673A® in fermenter is comprised between 0.01% and 0.1% v/v; d) harvesting and collecting 2 g/L to 2.5 g/L of Neisseria meningitidis A capsular polysaccharide. <EOS>