When the dried sweet potato concentration was increased from 136.36 g L−1 to 168.22 g L−1, the productivity and lactic acid concentration increased from 2.55 g L−1 h−1 to 2.92 g L−1 h−1 and from 122.49 g L−1 to 151.59 g L−1 after 48 h and 52 h, respectively.