A method for the preparation of food coloring, including crushing of raw materials, soaking, reflux extraction, filtration, concentration, etc., characterized in that: the specific steps are as follows:

(1) Raw materials: the selection of botrytis cinerea fungi bamboo yellow, in a ventilated place to dry or sun-drying; (2) crushing: drying the bamboo yellow crushed; (3) soaking: the crushed particles of the bamboo yellow soaked in ethanol in the airtight, the weight/volume ratio of the bamboo yellow and ethanol is 1/4-1/6 (g / ml); (4) reflux extraction: the ethanol infusion reflux 1.5-1/6 (g / ml). The weight / volume ratio of bamboo rhubarb and ethanol is 1/4-1/6 (g / ml); (4) reflux extraction: reflux the above ethanol infusion of bamboo rhubarb for 1.5-2.5 hours, leaving the filtrate, the filtrate with ethanol and then refluxed, *** Repeat reflux for 2-4 times; will be each time to reflux to get the extract filtration; (5) Combined standing: the extract of each filtered mixture, 0-10 ℃, standing 10-30 hours; (6) concentration: the combined extract again filtered to remove ethanol, concentrated into a paste pigment.