Process Adjustments at High Altitudes
Using the process time for canning food at sea level may result in spoilage if you live at altitudes
of 1,000 feet or more. Water boils at lower temperatures as altitude increases. Lower boiling
temperatures are less effective for killing bacteria. Increasing the process time or canner
pressure compensates for lower boiling temperatures. Therefore, when you use the guides,
select the proper processing time or canner pressure for the altitude where you live. If you do not
know the altitude, contact your local county Extension agent. An alternative source of information
would be the local district conservationist with the Soil Conservation Service.
Equipment and Methods Not Recommended
Open-kettle canning and the processing of freshly filled jars in conventional ovens, microwave
ovens, and dishwashers are not recommended, because these practices do not prevent all risks
of spoilage. Steam canners are not recommended because processing times for use with current
models have not been adequately researched. Because steam canners do not heat foods in the
same manner as boiling-water canners, their use with boiling-water process times may result in
spoilage. It is not recommended that pressure processes in excess of 15 PSI be applied when
using new pressure canning equipment. So-called canning powders are useless as preservatives
and do not replace the need for proper heat processing. Jars with wire bails and glass caps
make attractive antiques or storage containers for dry food ingredients but are not recommended
for use in canning. One-piece zinc porcelain-lined caps are also no longer recommended. Both
glass and zinc caps use flat rubber rings for sealing jars, but too often fail to seal properly.
Ensuring High-quality Canned Foods
Begin with good-quality fresh foods suitable for canning. Quality varies among varieties of fruits
and vegetables. Many county Extension offices can recommend varieties best suited for canning.
Examine food carefully for freshness and wholesomeness. Discard diseased and moldy food.
Trim small diseased lesions or spots from food.
Can fruits and vegetables picked from your garden or purchased from nearby producers when
the products are at their peak of quality-within 6 to 12 hours after harvest for most vegetables.
For best quality, apricots, nectarines, peaches, pears, and plums should be ripened 1 or more
days between harvest and canning. If you must delay the canning of other fresh produce, keep it
in a shady, cool place.
Fresh home-slaughtered red meats and poultry should be chilled and canned without delay. Do
not can meat from sickly or diseased animals. Ice fish and seafoods after harvest, eviscerate
immediately, and can them within 2 days.
Maintaining Color and Flavor in Canned Food
To maintain good natural color and flavor in stored canned food, you must:
•Remove oxygen from food tissues and jars,
•Quickly destroy the food enzymes,
•Obtain high jar vacuums and airtight jar seals.
Follow these guidelines to ensure that your canned foods retain optimum colors and flavors
during processing and storage:
•Use only high-quality foods which are at the proper maturity and are free of diseases and bruises.
•Use the hot-pack method, especially with acid foods to be processed in boiling water.
•Don't unnecessarily expose prepared foods to air. Can them as soon as possible.
•While preparing a canner load of jars, keep peeled, halved, quartered, sliced, or diced
apples, apricots, nectarines, peaches, and pears in a solution of 3 grams (3,000
milligrams) ascorbic acid to 1 gallon of cold water. This procedure is also useful in
maintaining the natural color of mushrooms and potatoes, and for preventing stem-end
discoloration in cherries and grapes. You can get ascorbic acid in several forms:
Pure powdered form-seasonally available among canners' supplies in supermarkets.
One level teaspoon of pure powder weighs about 3 grams. Use 1 teaspoon per gallon of
water as a treatment solution.
Vitamin C tablets
Commercially prepared mixes of ascorbic and citric acid-seasonally available among
canners' supplies in supermarkets. Sometimes citric acid powder is sold in supermarkets,
but it is less effective in controlling discoloration. If you choose to use these products,
follow the manufacturer's directions.