This method ferments a milk starting material by using a and a that have the property of maintaining at least a 30% survival rate of the when a culture medium containing, for example, 1% (W/W) glucose and 10% (W/W) reduced skim milk is inoculated with 5.0×10 to 2.0×10 CFU per 1 ml of culture medium of a that does not have a cell-wall-localized protease and 1.0×10 to 3.0×10 CFU per 1 ml of culture medium of a bacteria, the bacteria are cultured, and when the pH of the culture medium has reached 4.6 to 5.5, the culture medium is rapidly cooled from the culturing temperature to 10°C and stored for two weeks at 10°C.
