invitro said:

The main enemy of efficient  heating in a closed vessel (e.g. a retort) using
saturated steam  is the presence  of entrapped air, especially  that trapped  in the
small spaces between containers in the load. Even a small quantity of air has a
significant effect upon the temperature. For example, at any given location 10%
of air by volume will reduce the temperature by about 3º C, which will have a
dramatic effect on product sterilisation. This means that in order to bring about efficient and uniform heating, air must be purged, or as it is referred to in the industry, 'vented' from the retort at the start of the process

ftp://ftp.feq.ufu.br/Luis/Books/E-Books/Food/Thermal_technologies_in_food_processing/3558x_02.pdf
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Venting stage -
Air trapped inside the retort is removed prior processing.If air is present at a given pressure the temperature inside the retort will be lower than that attained by steam alone.A mixture of air and steam may stratify leading to cool spots where there is air. This mixture is a less efficient heat transfer medium than steam alone. Air in the retort cuts down the heat penetration of steamby insulating the cans and can accelerate external corrosion

http://www2.tust.edu.cn/jingpin/jp2007/spjsyl/pdf/Thermal%20Processing-%20Canning.pdf

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There does seem to be an agreement among commercial operators that venting is critical for efficiency. 

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SO, it got me thinking a lot harder about whether or not these bags are good to go, and whether or not I want to hit them with a perfectly good master jar of spawn if it isn't properly sterilized.

These are six pound bags, 15 PSI for 120 min, with jar rings between the bags and walls of PC for steam movement per Roger Rabbits recommendation. I am a bit worried that these bags might not be ready to go because of the above mentioned reasons and I want to know if it will hurt anything to PC the questionable bags twice? Or should I just treat this as an experiment and see how they do compared to my other bags?
PEACE!

Tstone said:

First few times using my PC, I didn't vent, never had a problem ( perhaps lucky) I'm unsure about 6 lb grain bags and PC time in general. I do qt jars. Normally double pc-ing grains is not recommended, cause it messes with moisture content.

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Tstone said:

Are you using spores, G2G, agar to inoculated bags? Spores are the most finicky to germ, if moisture content is too wet or too dry gonna have issues with germination. 

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Tstone said:

Personally, if I had the extra cultures or spores and limited grain, I would inoculate for the helluva it, results could be questionable ( have a back up plan).  I would not double cook. If I had enough grain at my disposal, limited cultures / spores, and want a more predictible out come, start over. There is the comfort level from the get go that the grains were prepared properly.

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Well I do have a good number of jars that I made from MS, and I decided to just proceed with inoculating these bags "for the helluva it" to see how they pan out compared to the other bags I did differently/"better". I want to learn as much as I can, and since I am keeping good notes, I will be able to trace back any problems. This way I will have more of a working knowledge of what works, and what doesn't. This way I won't be spending crazy amounts of time over PCing grains (I have seen all kinds of crazy recommendations on here that would cause you to spend half of your life by the pressure cooker. For now I'll stick with trusty ole' Roger Rabbit's recommendation of 120 min)

Will keep fingers crossed, keep good notes, and see how it goes.

These are bags I G2Ged three days ago, should be 100% in less than a week. Fingers crossed for the others.