If it is bigger, it will take more than 30 minutes to steam. After steaming for 20 minutes, put a few sweet potatoes with chopsticks. If it can penetrate easily, it means that the sweet potato is ripe.
Under normal circumstances, when steaming sweet potatoes, use a big fire first. When the water in the pot is boiled, turn to low heat and steam for 10 to 15 minutes. According to the size of sweet potato, the big one should be steamed longer and the small one should be steamed faster.