23q Presto Steam Penetration test

The lid holes are actually 1/4"*
Testing the load penetration capabilities of the 23-quart Presto pressure canner by inserting type 4 steam indicator strips into grain (un-cooked/un-hydrated) jars to ascertain both penetration and cycle function.
One cubic foot of water will become 1646 cubic feet of steam when evaporated at zero psi gauge pressure and a temperature of 212°F. One cubic foot of steam weighs 0.03732 pounds, and one pound of steam occupies 26.796 cubic feet at zero psi gauge pressure and a temperature of 212°F.
Steam occupies 1600x more volume than liquid water, this is an important feature of steam sterilization because voids of trapped gasses reduce internal temperature and sterilization cycle efficiency. To ensure trapped gasses are evacuated, the unit must be purged by boiling the water under the trivet. By allowing the water to boil sufficiently before applying the weight, the energetic expansion of the steam forces trapped gasses to escape via the vent tube; replacing the cold/dry encapsulated gas with steam by virtue of this exponential expansion slightly pressurized by the sealed cooker and small diameter of the vent tube.
Longer purge times are required for larger units like the All-American 941(x) or the 75x. Allow 30 minutes to purge the larger internal volume units.
Pressure allows water to exceed 100°C, the resulting steam is saturated with latent heat reaching 121°C at 15psi (at sea level, be sure to adjust for elevation where applicable). Steam contact and latent heat are the mechanisms by which the microorganisms and viruses have their DNA/proteins denatured during the cycle, including pesky thermophilic bacterial endospores.
The pressurized steam makes contact with load surfaces, penetrating voids to condense and make contact with microorganisms. While purging is necessary to penetrate voids in the media and to achieve sterilization temperatures, clean/rinsed grains are required to take full advantage of these mechanisms. An overburden of filth not only increases bioburden/bioload but prevents contact with the grain surface where CFUs (colony-forming units) reside.
If steam didn't penetrate the load, it wouldn't transfer latent heat to the surface upon which it condenses to denature the proteins of microorganisms (Where voids are present). Failure to penetrate the load will result in cold/dry spots insulated by trapped gas and media which will result in CFU survival, resulting in contamination. This is why longer purge and exposure times are preferable.
The difference between pressure canners employed for canning and autoclaves employed for sterilization purposes:
Canning takes advantage of pressurized steam to quickly cook, sterilize, and seal jars without requiring steam penetration because canners rely on convection to cook food products with significant moisture content. The closed canning jars with metal 2-piece lids pull a vacuum and then self-seal to prevent spoilage. Steam penetration is not required to process liquids.
Autoclaves function by penetration and direct contact with saturated steam which condenses on load surfaces to kill microbes and viruses. We've simply repurposed pressure canners to function as autoclaves.
Labs and dental offices employ class-b autoclaves with vacuum pumps in conjunction with fractional surge cycles to evacuate trapped/dry gasses and to penetrate deep into complex loads; How deep, you ask? The Helix test contains a chemical test strip at the end of a coiled 1.5-meter length of surgical tubing, the steam must enter and travel the entire length of the tubing to make contact with the steam indicator strip.
We do not have the benefit of vacuum pumps or vacuum purge cycles, so it's important to allow for ample warm-up, purge, and cycle time exposure to ensure an appropriate Sterility Assurance Level (SAL).