To Can or Not To Can is the Question
What Shouldn’t be Canned
Besides the pH issues there are some other foods that make canning difficult. For instance, how gooey foods are, play into the canning process. Foods such as pumpkin and squash purees are not the best things to can. These thick liquids make it difficult to heat through, creating cold spots in the middle, which allow bacteria to grow and become prevalent in your canning process.
Other items, which shouldn’t be canned, for much the same reason, are refried beans, butter and leafy greens, like spinach and chard also make it difficult to can due to the cold spots in the middle of the food. Creams and soups also have a difficulty with canning because, you guessed it, and they become scorched and curdled on the outside while trying to raise the temperature in the middle.
What Should be Canned
On the flip side, if you have pumpkin and squash that you would like to can, putting them in a jar in raw chunk form will allow them the proper canning temperature in a pressure canner. It also begins to moisten them up for later use. Other than that, just about everything falls into the category of able to be canned. Foods such as lemons, plums, figs, apples and some tomatoes can be home canned with ease.
Here is a brief list of foods and their respective pH levels, which are good for canning:
A. pH 2.0-3.0 - Lemons, limes, gooseberries and under-ripe plums
B. pH 3.0-3.5 - Ripe plums, under-ripe apples, ripe oranges and
grapefruit, strawberries, rhubarb, blackberries, cherries,
raspberries, blueberries, very under-ripe peaches and apricots
C. pH 3.5-4.0 - Ripe apples, oranges, grapefruit, overripe
blackberries, cherries, raspberries, and peaches, ripe apricots,
under-ripe pears, pineapple, sauerkraut and other pickled items
D. pH 4.0-4.6 (BORDERLINE) –Tomatoes and figs Above 4.6 or so, must
be pressure canned.
E. 4.6-5.0 - Some tomatoes, depending on the variety (Green
tomatoes are below 4.6). Pimentos, pumpkin. The USDA suggests that
pumpkin butter cannot be canned safely.
F. 5.0-6.0 - Carrots, beets, squash, beans, spinach, cabbage,
turnips, peppers, sweet potatoes, asparagus, mushrooms, white potatoes
G. 6.0-7.0 - Peas, tuna, lima beans, corn, meats, cow's milk, salmon, oysters, shrimp.
Be sure to note the food items that are borderline and must be pressure canned to be safe. Remember that butters and other purees which are thick are better not canned. Check out the USDA site on the Internet if you’re not sure which foods will remain safe after being put through the canning process.