Yes. Otherwise you'll end up with hot spots or dough balls. I add water, grain, stir. Add more water, the rest of the grain, stir. Then I add the remaining water, stir and then take the temperature and adjust accordingly ( hot water if too low, cold water if too high ). I find with my setup ( 70 qt rect. Coleman cooler ) it takes a good 5 minutes or so for the temperature to stabilize.