A method for controlling the milking by a milking machine comprises the steps of: (i) controlling (47) a milking vacuum so that the milking vacuum is varied through the vacuum levels of a given range, while a milking animal is milked by the aid of the milking vacuum; (ii) monitoring (43) a milk flow from the milking animal during the variation of the vacuum levels; (iii) setting (49) the milking vacuum to the lowest vacuum level of the given range, for which the milk flow from the milking animal is at least a given fraction of the highest milk flow monitored while the milking vacuum is varied; and (iv) keeping (51) the milking vacuum at the set vacuum level during a following part of the milking of the milking animal.