I see the word sterile thrown around on various brewing sites and discussion groups a lot – too much. I think it is important for people to understand the difference between what can be considered sterile and what can be considered sanitary.
After cleaning your equipment for brewing, you should sanitise your equipment. This process is almost always done with some kind of chemical, usually StarSan or Iodophor and in some cases people use bleach. The process of sanitising will kill the vast majority of microorganisms that are on your equipment, over 99% of them. This does not, however, make your equipment sterile, yet it is enough for our home brewing needs.
In order for your brewing equipment to be considered sterile, you would have to remove 100% of all microorganisms. Certain types of bacteria, known as spore forming bacteria, can resist your attempts to kill them by forming an endospore. These endospores are little protective capsules that the bacteria can hide in that protect them from various chemicals and even heat. It is these very endospores that allow Clostridium botulinum to survive in improperly canned food and make you sick.
There are many ways to sterilise, with the most common home method being heat and steam/pressure; this is the principle applied when canning and anyone who has worked in a lab will be familiar with an autoclave. There are charts available to see the required temperature, pressure, and time to sterilise using this method. Other sterilisation methods include dry heat for long periods of time, various chemicals likely too dangerous for home use, and radiation – also too dangerous for home use and probably illegal.
When it comes to your brewing equipment, however, you don’t need it to be sterile, you just need it to be sanitary. The environment created by fermentation is inhospitable to bad microorganisms and all you’re really trying to do is establish the microorganism(s) that you want in there before anything else can creep in. It would also be quite difficult to actually sterilise your home brewing equipment give the size of things like kettles and fermentors, and the likely high heat intolerance of the glass and plastic fermenting vessels most of us use.