Inulin preparing method taking dried jerusalem artichoke as raw material

The invention relates to the technical field of new resource food processing, in particular to an inulin preparing method taking dried jerusalem artichoke as the raw material. The jerusalem artichoke or chicory is taken as the raw material and is subjected sequentially to peeling, dicing and expansion drying, and dried jerusalem artichoke cubes are obtained; then continuous countercurrent extraction is performed; and an extracting solution enters an ion resin-column for desalination after being subjected to impurity removal and activated carbon decoloration, then is concentrated by a nanofiltration membrane, and then is subjected to spray drying, therefore, high-purity inulin is obtained. The countercurrent extraction adopts purified water, the solid-to-liquid ratio is 1:(5-10), the extraction temperature ranges from 80 DEG C to 100 DEG C, and the extraction time is one hour to two hours; in the processes of impurity removal and decoloration, Ca(OH)2 solids are added first, the pH of the system is regulated to be 10 to 12, CO2 gas is introduced after 30 minutes to enable the PH of the system to be 7 to 8, precipitates are filtered, activated carbon is added for 30 minutes of decoloration and then is filtered out, and a filtrate is reserved; and the adding amount of the activated carbon is 1-5 per thousand of the total weight of the system.