Canning preserves food by using heat to kill any bacteria that can cause illness or spoilage and creates and airtight seal to prevent future spoilage.
There are two methods of canning, boiling water bath and pressure canning. The method used depends on the acidity of the food. High acid foods with a pH balance equal to or more than 4.6 would use a boiling water bath, while low acid foods with a pH balance below 4.6 would use a pressure canner.
|pH = < 4.6 High Acid Foods|
|WATER BATH CANNER|
pH > 4.6
Low Acid Foods
The proper canning method must be used to prevent botulism (Clostridium Botulinum) which is often found in the soil and is found in two forms. The first form is vegetative cells (active cells which produce a deadly toxin), Vegetative cells are anarobic (can live without oxygen) and are kill by boiling in water 212 degrees. The second form is spores which are often in the soil and are inactive and in hibernation. Spores can only be killed if they are boiled at 240 degrees which must be done with a pressure canner. Botulism loves a low-acid environment.
|Turnips||Meat and Poultry|
| PRESSURE CANNER|
A boiling water bath uses a large covered cooking pot with a rack. The pot must be deep enough to at least one inch of water covers the top of the jars during processing. The diameter of the pot should be no more than 4 inches wider than the diameter of the burner. Again, this method is used most often when canning high-acid foods such as tomatoes, most fruits, jellies, jams, and pickles.
Pressure canning uses a special type of canner that has a lid which is able to be tightly closed so steam cannot escape. The pressure generated in this type of canner allows the food to be heated at temperatures higher than 212 degrees (boiling temperature). This is the recommended method of canning for low acid foods like most vegetables, meat, and poultry.
You should only ever can using a boiling water bath using a pot on the stove or using a pressure canner on the stove. Do not use an open kettle, steam canning, microwave oven canning, oven canning or dishwasher canning, as these are all unsafe methods.
Also, you should only use recipes that have been tested using research -based methods. Recipes from cookbooks, family, and some internet sites may not be safe to use. And DO NOT alter or make up your own recipes, because it is not safe.
You can get tested recipes from current Extension publications, USDA, and makers of home canning equipment and ingredients.
DO NOT use personal internet sites, cookbooks, "back to nature" publications, or out-of-date Extension publications.
When canning use mason-type jars that are made for home canning. Sizes of jars vary; pint and quarter sizes are most common, and half-pint jars are used most often for jellies and jams. Be sure to use regular and wide-mouth jars. Most canning jars have a life span of about 13 years.
Headspace is the space in the jar between the underside of the lid and the top of the food or its liquid. The amount of headspace needed depends on the type of food and the method of canning used, which you will find stated in the recipe.
If you have too little headspace, food may boil over onto the rim of the jar and prevent it from sealing properly, and if you have too much hefadspace the processing time may not be enough to get all the air out of the jar, resulting in a poor seal and may also result in discolored food.
Once the jars are filled, release air bubbles by placing a flat plastic spatula between the food and the jar, adjust the headspace, wipe the jar rim with a damp paper towel, and place the lid on the jar, add the screw band and slightly tighten (not too loose or too tight).
The processing time is the length of time the jars are in the canner so foods are properly heated and the lids sealed. This time kills the bacteria in the food so spoilage or foodborne illness doesn't happen, and is a critical step in food preservation. Processing times depend on the the food, the size of the jar, and the type of canner.
High altitudes can change the processing times.
|Food||Jar Size||Usual Time (< 1000 feet)||1001-3000 ft||3001 - 6000 ft|
|Water Bath Canning|
|Crushed Tomatoes||quart||45 minutes||50 minutes||55 minutes|
|Jelly||quart||varies||Add 1 minute of processing time per 1,000 ft of altitude|
|Green Beans||quart||25 minutes||Process time depends on altitude and type of pressure canner (dial vs. weighed gauge)|
After processing, make sure your jars are sealed. Press the middle of the lid with your finger. If the lid springs up when you lift your finger the seal is NOT good. While cooling you may hear a "pop" noise coming from the jars. This is a sign that the lids have sealed but it is a good idea to check them again 12 to 24 hours later.
If you notice a jar that did not seal within 24 hours of processing, you have three options:
- Refrigerate the contents and eat in a few days
- Reprocess using a NEW LID and the FULL processing time.
If the jars did not seal and it has been longer than 24 hours, those jars should be thrown away.
Remove the screw bands and wipe the jars to remove any food residues. Label and date the jars, then store in a clean, cool, dark, dry place.
Example Jar Label:
07/08/2015 = Date the jar was processed
B-2 = second batch of jars processed
Okra = food processed
You should throw out home-canned foods when:
- The jars were not processed correctly
- There is unexplained clouding canning liquid occurs
- There is a strange odor
- There is mold growth
- The jar did not seal and it has been longer than 24 hours
- The lid is bulging
- Has reached 1 year after processing date
Source: National Center for Home Food Preservation, Georgia Cooperative Extension, So Easy to Preserve 5th ed., and Food Safety Advisor Volunteer Handbook, Washington State University and University of Idaho.