High acid foods
Lemon Juice
Cranberry Sauce
Gooseberries
Rhubarb, Dill Pickles
Blackberries
Applesauce, Strawberries
Peaches
Raspberries, Sauerkraut
Blueberries
Sweet Cherries, Apricot
Tomatoes
Low acid foods
Figs, Pimentos
Pumpkins
Cucumbers
Turnips, Cabbage, Squash
Parsnips, Beets, Green Beans
Sweet Potatoes
Spinach
Asparagus, Cauliflower
Carrots
Potatoes
Peas
Corn
Holding of produce to be canned for long periods in warm summer
temperatures gives bacteria ample time to multiply into vast numbers,
thus increasing the chances of spoilage.
For example, one cell can multiply into a billion cells in just 15 hours
of holding under favorable conditions.
Salt and spices added to low-acid canned products in amounts recommended
do not appreciably alter processing time. Salt may slightly lower the
heat resistance of some micro-organisms but not enough to present a
problem if omitted for dietary reasons.
Fats and oils, if added, may reduce the rate of destruction of bacterial
spores. Spores of _C. botulinum_ have been known to survive beyond all
reasonable expectation when heated in oil suspensions. Thus, adding oil
or fat to a product being canned could be dangerous and is not
recommended.
The type, consistency, and piece size of food and how it is packed in
the jars are important factors which affect processing time. In
preparing jars of food for the pressure canner, follow directions
carefully. Do not use jars larger than the directions specify.
Determining the safe processing time for a food product involves two
important steps.
First, the rate of heat penetration is measured by finding the spot in
the jar that takes the longest time to heat. This is referred to as the
"cold spot". Times will depend on the type of food (squash vs tomato
juice) as well as how it is prepared (whole kernel vs cream style corn).
The second step is done in a laboratory. A known amount of some live
bacterial spores is put into the "cold spot" of the jar of food. These
jars are then heated and the amount of time needed to kill the spores is
determined.