How can porridge cooked in summer not go bad?

It is best to put it in the refrigerator after cooling and solve it the next day at the latest; But I heard that if you cook with fire, put the pot on the iron knife, so it's generally no problem to spend the night. I don't know if it will work, because I haven't tried that way, hehe ~ ~ If I try it, remember that it must be an iron knife, not that kind of stainless steel.