posted 10 years ago
Two or three additional points, on jar breakage and also seal failure:
--Supposedly one must never use a metal implement, especially a sharp edged or pointed one, to pack food down or release air bubbles from jars when filling. These tools can leave nearly invisible, hairline scratches on the glass, where cracks are triggered to form later from whatever direct cause.
--When pressure canning it is vital to exhaust the canner, then bring it to pressure and keep the pressure even the entire time required to process. If the pressure fluctuates too much or too dramatically (such as by canning over a campfire or trying to multitask too much----I have done both!), this can cause failures. When processing is done, the closed cooker must be allowed to depressurize of itself, without opening before the gauge reads zero or trying to hasten the process with cold water, etc.
--This is a suspicion of my own that I haven't read about anywhere and is on the cutting edge of my own trial-and-error research....."exhausting" the canner means to allow the canner to boil with the valve open until a steady stream of visible steam is seen to come from this for the allotted time (usually 7-10 minutes) before closing the valves and bringing to pressure. I think this process of replacing all the hot air inside the pot with steam is made more difficult if the canner is only partially full of jars.....it stands to reason that the more empty space there is in there the longer this will take and the more likely it will be incomplete. So I've made up several dummy jars full of water and from now on will fill a partially full canner up to full with these.