Many foods are great for canning, but not all foods. There are some food items that don’t come out very well, and there are some that simply are not safe to preserve by canning. Let’s look at some of the do’s and don’ts when choosing foods to can.
Not All Foods Can Be Canned
The confusion starts when you talk about the acid levels. The term “pH” is a measure of acidity; the lower the number, the more acidic the food. Food between 2.0 and 6.9 pH levels are usually okay to can at home, but only if you use the right method of canning. A food item with a pH over 6.9, such as black olives for instance, becomes difficult to can in any method because they have to be specially cured before the storage process begins.
Along with the pH issues, there are other reasons why some foods are difficult to can. For instance, you have to take into account the “gooey” texture or density of a food. These gooey foods, such as pumpkin and squash purees, are difficult to heat through, even in a pressure canner, creating cold spots in the middle which allow bacteria to grow. In order to can pumpkin and squash properly, the USDA recommends putting them in the jar in chunks rather than puree, to allow the food to reach proper canning temperature in a pressure canner.
Other items which are difficult to can properly for much the same reason, are refried beans and leafy greens like spinach, kale, or chard. Again, this is due to the cold spots in the middle of the food. Thick, creamy soups and chowders may become scorched and curdled on the outside while trying to raise the temperature in the middle.
Learning Which Foods Can Be Canned
As in the example of the pumpkin and squash, some foods can be canned safely if prepared, cut, and processed in a specific way. However, the acid level must be part of the formula when you consider what foods are safe to can, and how. Foods with low pH levels are safely canned in a water bath canner, but as the pH levels rise, only a pressure canner will work. Here is a brief list of foods and their respective pH levels, which are good for canning:
- High acid foods – can be processed in hot water bath canner:
pH 2.0-3.0 – Lemons, limes, gooseberries and under-ripe plums
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
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
- Borderline pH level – may need to be acidified:
pH 4.0-4.6 – Some tomatoes (green tomatoes) and figs. Adding acid allows for tomatoes and figs to be canned in hot water bath. Without added acid, tomatoes must be processed in pressure canner.
- Low acid foods – must be processed in pressure canner:
pH 4.6-5.0 – Most tomatoes. Pimentos, pumpkin. The USDA suggests that pumpkin butter cannot be canned safely.
pH 5.0-6.0 – Carrots, beets, squash, beans, spinach, cabbage, turnips, peppers, sweet potatoes, asparagus, mushrooms, white potatoes
pH 6.0-7.0 – Peas, tuna, lima beans, corn, meats, cow’s milk, salmon, oysters, shrimp.
Again, food items with a pH of 4.6 or higher must be pressure canned. However, tomatoes are often canned in a hot water bath canner, but only if acid is added to the recipe.
The USDA site is always a good place to check when determining which foods can be properly canned and which ones are not recommended. Their website can be found by clicking on this link: National Center For Home Food Preservation
Or visit your local county or state extension office.
For more canning tips and lots of canning recipes, I recommend you grab a copy of my ebook Canning Made Simple.Inside you’ll find over 40 canning recipes to get you started, along with simple to understand explanations about what to can, how to can, and even why to consider canning at all!