What factors you should consider when canning

Now that the Christmas season has ended I start to think about spring and all the tasty fruits and vegetables that the warmer season brings. This is the time of the year that I begin to think about canning.

Whether you are a newbie canner or an experienced one when canning you should take into account several factors, like the acidity of the food, the processing time and the altitude of your area.

In canning we divide the food depending from the level of acidity in two categories: high acidity or low acidity food. So, in dependence from the acidity level of the food you can choose whether to boil the food or use a pressure canner.

Foods that are not processed properly can be the cause of botulism (that is caused by the Clostridium botulinum bacteria). This bacteria is quite heat resistant meaning that you must use high temperature to eliminate it. 

In foods with high acidity levels, such as fruit, pickles or tomatoes the growth of this dangerous bacteria is prevented by the high acidity level of the foods, meaning that the botulism spores can be destroyed quicker when boiled (using a boiling-water bath at 212°F). The boiling-water bath destroys the most common microorganisms that cause food spoilage as well as  mold and yeast.

Most tomatoes have an acidity level that is high enough but there are some varieties that have a lower level of acidity. In these cases you can add lemon juice or citric acid in order to ensure higher levels of acidity.

High acidic foods are: apples, apricots, blueberries, plums, oranges, peaches, pears, strawberries, grapefruit, grapes, cherries, pineapple, cranberries, raspberries, pickled cucumber, tomatoes.

If you want to prevent the growth of the botulinum bacteria in low-acid foods, such as vegetables, meats and seafood, you must pressure can the food at 240°F. If you would process low acidic food using a boiling-water bath it would take you very lengthy periods of time to do it (the length of time ranges from 7 to 12 hours). On the other hand, using a pressure canner and a temperature from 240°to 250°F it will take you just 20 to 100 minutes, depending on the type of food and the size of the jars.

Low acidic foods are: mushrooms, artichokes, beans, asparagus, peas, broccoli, beets, peppers, cabbage, potatoes, pumpkin, cauliflower, spinach, carrots, squash, corn, eggplant, figs.  

When you’re canning it’s very important to use the proper temperature and processing time.

Several factors affect the amount of processing time that is required:
- The canning method that you choose: pressure canning is faster, while using the boiling-water bath method takes more time. 
- The size of the food that you are canning: bigger pieces will take more processing time.
- The size of the jars that you are using: you will need more time if the jars are bigger.
- The pack method that is being used for the food: food that is raw packed requires in general more processing time (especially if the jars are bigger).
- The amount of liquid in the jars: if there is more liquid in the jars the contents will heat more quickly.

The altitude of your area is a factor you should consider as well. At sea level water boils at 212°F, while at higher elevations water boils at lower temperatures. Because of that, the boiling temperature at higher elevations is not enough to kill the harmful bacterias, so, if you are using the boiling-water method you need to increase the processing times of boiling, and if you are using a pressure canner you have to increase the PSI (or the amount of pressure). If processing times at sea level are 20 minutes or less at higher elevations you need to add 1 minute per 1000 ft. in elevation. When processing times at sea level are over 20 minutes you need to add 2 minutes per 1000 ft. in elevation. In pressure canning the processing times remain the same but you have to increase the pressure (usually from 10 to 15 PSI).

In my canning I use an All American Pressure cooker/canner and in my opinion this is the best pressure canner you can find. Read here my review.


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