In typical production of stirred yoghurt the incubation period is 2.5 to hours at 42-43°C when the ordinary type of bulk starter(2.5-3% inocu- lum) is utilised. The short incubation time indicates that the multiplication generation) period is fast. For typical yoghurt bacteria the generation period is some 20-30 minutes. To attain optimum quality conditions, cooling to 15-22°C(from 42-43°C) should be accomplished within 30 minutes after the ideal pH-value has been reached to stop further developement of bac- teria. Where concentrated, frozen or freeze-dried cultures are added direct- y to the yoghurt incubation tanks, a longer incubation time, 4-6 hours at 43°C, is necessary on account of the longer lag phase).