Putting Food By - Janet Greene [23]
Convection
Cut vegetables with added liquid and fruits in syrup of their own lavish juice depend greatly on convection for safe processing. In such packs, the heat seems to spiral inward from the sides, the swirls growing larger as they circle down and back up and closer toward each other, until eventually they touch and expand down to deal with the cold zone; this cold area, in convection, has lain in the center of the bottom one-fourth of the container.
Other Factors in Heat Penetration
There are still more considerations to be dealt with before the length of the heat can be specified.
1. How big is the container—and is it slender, or squat? These are questions concerning procedure, not prettiness. Naturally a big jar or can will take longer to heat through than a smaller one; and a short, chunky shape may have a cold zone that takes longer to heat than does a tall, slim one with greater actual volume.
2. How densely or loosely is the food packed inside the container? The less liquid in the container, the more worry you have that the food will be processed safely. (Remember the strained pumpkin that’s not for home-canning.)
3. There is a limit on the size of container that can be processed successfully at home, and we’re coming to that soon.
4. If you’re canning meat or a combination/convenience food: is it as lean and free of fat as possible? Fat insulates against heat just as it does against cold, and the more fat there is in a food, the slower the penetration by any heat.
Basic Equipment for Home-Canning
Some specialized canning equipment is essential for turning out safe and attractive products in return for your efforts, and it includes large canners for processing filled containers, and the containers (with their fittings), which are made to withstand the required heat treatments, and to seal well. These few special items—and their Whys—are described fully in the following pages; for all the rest, your regular kitchen utensils will be adequate.
A deep-enough, Water-Bath Canner—or a big stockpot—for processing strong-acid foods.
A 12-quart steam Pressure Canner for processing low-acid foods: with gauge(s) of tested accuracy.
A 6- to 8-quart enameled or stainless steel kettle for precooking or blanching foods to be canned.
Jars or “tin” cans in prime condition, with lids/sealers/gaskets ditto. Sealing machine (hand-operated), if you’re using cans.
Alarm clock, to time processing longer than 1 hour—plus a minute-timer with warning bell (more accurate than an alarm clock and better for processing less than 1 hour)—plus a clock with a sweep second-hand (if you go in for quite brief 15-psi processing).
Pencil-shaped glass mercury food thermometer which you’ll need for meats, poultry, and seafood in jars, and for all foods in cans. An instant-read thermometer can also be used, but only one that can be calibrated. Consult the manufacturer’s instructions and be sure to calibrate before use. The most accurate are thermocouple thermometers, which are used in scientific laboratories and by the food industry. However, these are very expensive. Of the more reasonably priced instant-read thermometers marketed for household cooking purposes, those with digital readouts tend to be more accurate than dial types. Never test food for canning with a dial-type candy/deep-fry thermometer or with a dial-type meat thermometer designed to be kept in a roast throughout cooking. These can be way off.
Shallow pans (dishpans will do).
Wire basket to hold foods for blanching.
Ladle or dipper.
Perforated ladle, skimmer, or long-handled slotted spoon, for removing food from its precooking kettle.