The title should have read BIAB PRESSURE canned wort. kombat is 100% correct. Here's a good read on the subject found in "Brew Your Own" magazine...
In home food preservation, foods are divided into high-acid foods, with a pH below 4.6, and low-acid foods, with a pH above 4.6. High-acid foods can be safely canned using the boiling water method. It is recommended that low acid foods be canned in a pressure cooker, where the increased pressure means that water boils at 240 °F (116 °C) or higher. The pH of boiled, unfermented wort is around 5.05.2, making it a low-acid liquid.
The reason for the high-acid/low-acid distinction is that spores of the bacterium Clostridium botulinum can survive in low-acid foods, even if they have been heated to 212 °F (100 °C). Clostridium botulinum produces 7 different classes of botulinum toxin, labeled A through G, and all are powerful neurotoxins. Botulinum type A, the most toxic, is 15,000 times more potent than VX nerve gas.
Botulinum toxins stop impulses in the nervous system from triggering muscular contractions. Symptoms of botulism usually arise 2436 hours after exposure to the toxin and include dry mouth, weakness, double vision, vomiting, depressed breathing and a progressively intensifying paralysis leading to death.
The presence of Clostridium spores in raw honey is why doctors recommend not feeding it to infants or small children.
Although spores of the bacteria are found almost everywhere, cases of botulism are actually relatively rare. Most years, around 110 cases are reported in the US, with most occurring in infants or small children that have eaten honey or other affected foods. On average, less than 30 cases per year result from improper home canning.
In fermented wort (i.e. beer), the alcohol content, low pH (4.04.4) and anti-bacterial components in hops prevent C. botulinum from surviving. In preserved, unfermented, lightly-hopped wort, it is possible for the bacteria to grow. Although the bacteria will die if the wort is fermented, any toxins produced by the bacteria will not be neutralized.
To minimize the possibility of botulinum poisoning, can your starter wort using a pressure cooker or add acid such as phosphoric or lactic acid to your starter wort such that its pH is 4.6 or below if you are using the boiling water method. (High hopping levels alone are likely not enough.)
The boiling water method is presented here because it has been used successfully for many years, but it does allow for the possibility of botulinum poisoning. Although the probability of this is low, the consequences can be severe if it does occur.
The pressure canner I use is an "All American" 941. It will hold 20 quart jars or 32 pint jars...or a combination of both. In the video I boiled for an hour for a combination of reasons. I needed some time to clean the jars; I only milled the grains once so the gravity came in at 1.025, so I needed time to boil it down to 1.040 before adding the cold water; & finally to boil off DMS? Don't know if it's necessary for a starter; but figured it wouldn't hurt anything.
ArcLight added a great tip As a result I'm thinkin..."Double Down" on the grain bill to condense the wort & pressure can 16 pints in the lower level. Then fill ten or eleven quart size jars with water on the top rack. What's leftover after diluting should be good for washing yeast...right?...