Citric acid is produced by submerged fermentation using fungus from different sources of carbohydrates, such as molasses and starch-based media. As precipitation, calcium oxide is added to form the slightly soluble tri-calcium citrate tetrahydrate. The precipitate is removed by filtration and washed to remove impurities. It is treated with sulphuric acid to form calcium sulfate and filtered off. The citric acid liquid is then treated with active carbon and passed through a cation and anion exchanger. Finally, the liquid is concentrated in vacuum crystallizers at 20-25℃, forming citric acid monohydrate. A higher temperature in this step will result in citric acid anhydrous.