When microbiological media has been made, it still has to be sterilized because of microbial
contamination from air, glassware, hands, etc. Within a few hours there will be thousands
of bacteria reproducing in the media so it has to be sterilized quickly before the microbes
start using the nutrients up. The sterilization process is a 100% kill, and guarantees that the
medium will stay sterile UNLESS exposed to contaminants by less than adequate aseptic
technique to exposure to air.