A method of treating green coffee beans is provided that can prevent contamination by acetic-acid producing bacteria when implementing a fermentation treatment on green coffee beans using microorganisms and that can impart new and favorable flavor and aroma to a coffee drink. This object can be achieved by a method of treating green coffee beans comprising a fermenting step for performing fermentation by bringing a nutritive substance and a fermenting microorganism into contact with one another and then supplying the fermented components thus formed to green coffee beans, wherein, in the fermenting step, the nutritive substance and the fermenting microorganism are brought into contact with one another in a pH range for inhibiting the growth of acetic-acid producing microorganisms.
