Safe as in is the food safe to eat? Yes. Safe as in is it safe to run the canner that way without risk? Yes as long as you are sure the over-pressure plug is in good working order, that gauge reading is accurate so that you know the real pressure, and if there was enough water in the canner to begin with so you don't risk it running dry due to all that excess steam escape.

But it isn't ideal in that it can result in over-processed food of lesser quality. Mirro canner weights are machined to jiggle/spin 3-4 times a minute when at pressure so continuous jiggling would indicate pressure in excess of 15.5 -16 lbs or more and if the guage is off even a little you'd have no way to know what the pressure was until the plug blew.

Dave.

This post was edited by digdirt on Thu, Feb 28, 13 at 19:55

Thanks Dave, I figured the food was safe and since it was just broth I wasn't worried about the product turning to mush. I was mainly concerned about overpressure risk which you helped to clarify. I will only do this again if I can arrange a better way to control temperature so that the weight will only jiggle at the proper frequency.

Mainly it's an issue of running out of water during the processing time, as Dave mentioned. However, another risk is too high a heat can fracture the PC as the Mirro and Presto vessels are pretty thin. I actually ended up with a crazed Presto because I failed to make appropriate adjustments when I bought a new range.

There's no reason not to can on a wood stove, but it is more of a learning curve in terms of managing the heat. One problem is the weight of a full canner generally precludes shifting it a bit to a cooler location.

Carol