A manufacturing method includes a granulation step. The granulation step is a step of forming a plurality of granules by performing extrusion granulation on a granulation material using a granulation machine. The granulation machine includes a die and a cutter. A through hole that allows the granulation material to pass therethrough is formed in the die. The cutter cuts the granulation material that has been extruded from the through hole while rotating along the back side of the die. In the granulation step, low-speed cutting in which the granulation material is cut while the cutter rotates at a first speed, and high-speed cutting in which the granulation material is cut while the cutter rotates at a second speed that is higher than the first speed are executed.
