7。 The hardness of ice cream must be 7. When the ice cream machine works, it is generally set according to the actual situation. For example, a brand of ice cream can set 7 hardness values, which can be adjusted from 1-7. Before operation, the hardness value can be set to 4, which can be adjusted according to the forming situation of ice cream cake. For the soft ice cream machine, there are few models that can directly adjust the temperature, which can be set to -7 degrees.