Method for producing citric acid fermentation liquor by two-stage fermentation

The invention discloses a method for producing citric acid fermentation liquor by two-stage fermentation. The method comprises the following steps: (1) Aspergillus niger mouldy bran spores are taken,sterile water is added in order to prepare a spore suspension, the suspension is inoculated to a seed tank and culture is carried out for 16-24 hours, in order to obtain seed liquid; (2) corn liquefaction liquid whose volume is 8-12% of effective volume of a fermentation cylinder is added into the fermentation cylinder, and the temperature is reduced to 35-39 DEG C; (3) seed liquid obtained in thestep (1) is inoculated to the fermentation cylinder, and cultivation is carried out for 2-8 hours; (4) a sugar solution whose volume is 60-64% of the effective volume is added into the fermentation cylinder for cultivation, and when reducing sugar is below 5g/L, fermentation is stopped, and citric acid fermentation liquor is obtained. The two-state cultivation avoids influences of pH reduction inearly stage of fermentatio