I'm doing a stout that calls for a final gravity of 1.016 - 1.020 but I've noticed with my set up that most of my beers finish a lot lower than that, regardless of the recipe. my guess is the temperature in my apartment is quite high but that's just a guess. anyway is it a good idea to kill the yeast when i reach the final gravity i want? or just let them go and hope for the best?