PROBLEM TO BE SOLVED: To provide a soft drink contained in a hermetically sealed container, effectively utilizing fulvic acid to achieve efficient mineral supplementation, with stabilized quality.SOLUTION: A drawn up natural water is passed through a primary filter 11 and a secondary filter 13 of 30 &mum or less for filtration, and the filtered natural water is accommodated in a mixing tank 30. Fulvic acid is passed through a prefilter 21 of 20 &mum or less for filtration prior to addition of the fulvic acid to the natural water accommodated in the mixing tank 30. The filtered fulvic acid is fed into the natural water in the mixing tank 30, and the natural water with addition of fulvic acid is passed through a final filter 40 of 0.2 &mum or less for precision filtration treatment, thereby performing sterilization and removal of off-taste, off-flavor, and impurities. Further, the natural water with addition of fulvic acid, sterilized by filtration, is filled into a container 60a at normal temperature by a non-heating sterilization method, and the container 60a is hermetically sealed with a cap 60b.
