Putting Food By - Janet Greene [29]
Reduce to Zero
At the end of the required processing time turn off the heat or remove the canner from the stove. It’s heavy and hot, so take care.
If you’re using glass jars, let the canner cool until the pressure drops back to Zero. Then open the vent very slowly.
CAUTION: if the vent is opened suddenly or before the pressure inside the canner has dropped to Zero, liquid will be pulled from jars, or the sudden change in pressure may break them.
If you’re using tin cans, the pressure does not need to fall naturally to Zero by cooling: open the vent gradually when processing is over and the canner is off heat, to let steam out slowly until pressure is Zero.
New Pressure Canners are designed to keep their covers locked so long as there is any pressure still built up inside.
Lift the Lid
Never remove the lid until after steam has stopped coming from the vent.
Open lid clamps or fastenings.
Raise the farther rim of the cover first, tilting it to direct remaining heat and steam away from you.
Take Out Jars or Cans Promptly
If the canner doesn’t have a basket rack, use a jar-lifter and dry pot holders (wet ones get unbearably hot in a wink) to remove jars/cans promptly. Promptness is important. Certain bacteria like heat, remember, and some types of spoilage are thermophilic.
Cool cans quickly in cold water.
Ignore the “after-boil” still bubbling in jars (this means a vacuum has already formed!) and complete seals if necessary. Stand jars on a wood surface, or one padded with cloth or paper, to cool away from drafts.
Test seals when containers have cooled overnight.
Dangerous Canning Don’ts
There’s nothing like the Morbidity and Mortality Weekly Report for discouraging nostalgic ways of canning food at home, because in almost every account of an outbreak of food-borne botulism, the Editorial Note deduces that “inadequate processing” or “inadequate heating” allowed the toxin to form, with the help of a bad seal.
Spelling it out, this means that low-acid foods that should have been Pressure-processed were merely given a Boiling–Water Bath; and that strong-acid foods—which should have been given a B–W Bath to sterilize container and heat contents adequately—were canned instead by “open-kettle,” or worse.
No to Old “Open-Kettle”
The first page of this chapter describes the origin of what was called open-kettle canning, a method whereby hot food—presumably fully cooked—was put into hot jars that once were sterile and were capped with hot lids that also once were sterile, and then usually a vacuum was formed as the contents cooled, helping to form the seal.
You see the problems. Jars, lids, sealing rims probably were sterilized carefully by being filled with, or lying in, boiling water. Fine. But then they sat for seconds or minutes in the open air of the kitchen while the contents were ladled in, and air-borne spoilers, some potentially deadly, contaminated the inside of jars and covers. The hot food simply was not able to re-sterilize the container; and indeed it may not have cooked quite long enough to destroy the bacteria that like heat approaching 212 F/100 C at the sea-level zone.
Mold is one of the leaders in the air-borne danger brigade, and it can settle on the underside of a canning lid and grow. In the process of growing it can metabolize the safe margin of acid just enough to allow surviving C. botulinum spores to develop and throw off their wicked toxin. So your jar of supposedly “safe” open-kettle-canned tomatoes—or dill pickles or jams or condiments or pears or peaches, all of which traditionally have been regarded as strong-acid enough to be protected—may contain a deadly threat. And aside from botulism, there could be mycotoxins from mold itself.
And No to Old “Oven-Canning”—or Microwaving
The folklore of homemaking has another bad method that continues to surface: trying to process foods by baking them. Please look back at How Heat Penetrates a Container of Food, early in this chapter. Dry heat just plain cannot