Why can't I process food at 10 lbs pressure in my dial gauge canner, instead of 11 lbs pressure, if I live between 0 and 1000 feet of altitude? I notice that it's alright to can in a weighted gauge canner at 10 lbs pressure if you live between 0 and 1000 feet.
USDA has determined that it is necessary to can at 10.5 lbs. pressure at 0 to 1000 feet of altitude to destroy botulism-causing bacteria, not 10 lbs. This corresponds to 240 degrees F. inside the pressure canner. This was rounded to 11 lbs. in dial gauge canners to avoid the confusion of half-pound recommendations. Weighted gauge canners are already machined to operate at 10.5 lbs. as a built-in-safety factor when they are set at 10 lbs. Since dial gauges at 11 lbs. have the extra half-pound pressure, it is safe to can up to 2000 feet altitude at 11 lbs. pressure. Weighted gauges set at 10 lbs. (really 10.5) are only safe for altitudes up to 1000 feet. Above 1000 feet, they must be set at 15 lbs. pressure. This is the main drawback of weighted gauge canners; they cannot be specifically corrected for altitude.
Last update: Tuesday, May 05, 2009