Do’s and Don’ts of Canning
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Spring is here and summer is around the corner which means the garden’s bounty is soon to follow. With so much beautiful produce available, you may be wondering how to put some of it up for the cold months. While canning foods is a great method of food preservation, we do want to make sure we use evidenced based resources to keep ourselves and those we feed from getting sick. These resources can also help to make sure your canned items preserve properly. So here is a list of the most frequently asked canning questions from The University of Georgia’s Cooperative Extension and their resource called “So Easy to Preserve.” We will be hosting two food preservation workshops this summer, one in May and one in June, so make sure you are on our email list to be notified of upcoming programs! Find the do’s and don’ts of canning below.
- Can food be re-canned if the lid does not seal?
Canned food can safely be re-canned if the unsealed jar is discovered within 24 hours. To re-can, remove the lid and check the jar sealing surface for tiny nicks. Change the jar; if necessary, add a new treated lid and reprocess using the same processing time.
- If canned foods have been frozen during storage, are they safe to eat?
Freezing does not cause food spoilage unless the seal is damaged or the jar is broken. These often happen as the food expands during freezing. Frozen foods, however, may be less palatable than properly stored canned food. In an unheated storage place, protect canned foods by wrapping the jars in paper or covering them with a blanket.
- If my recipe doesn’t call for processing, do I need to do so?
Many recipes passed down through the years or found in older cookbooks do not include instructions for processing. These foods are usually canned by the open kettle method, sealed and stored. Foods prepared in this manner present a serious health risk – particularly low acid foods. To minimize the risk of food spoilage, all high acid foods should be processed in a water bath canner or pressure canner and all low acid foods in a pressure canner.
- Do I really need to leave a certain amount of headspace in the jar?
Yes, leaving the specified amount of headspace in a jar is important to assure a vacuum seal. If too little headspace is allowed the food may expand and bubble out when air is being forced out from under the lid during processing. The bubbling food may leave a deposit on the rim of the jar or the seal of the lid and prevent the jar from sealing properly. If too much headspace is allowed, the food at the top is likely to discolor. Also, the jar may not seal properly because there will not be enough processing time to drive all the air out of the jar.
- How long will canned food keep?
Properly canned food stored in a cool, dry place will retain optimum eating quality for at least 1 year. Canned food stored in a warm place near hot pipes, a range, a furnace, or in indirect sunlight may lose some of its eating quality in a few weeks or months, depending on the temperature. Dampness may corrode cans or metal lids and cause leakage so the food will spoil.
- Is it necessary to sterilize jars before canning?
Jars do not need to be sterilized before canning if they will be filled with food and processed in a boiling water bath canner for 10 minutes or more or if they will be processed in a pressure canner. Jars that will be processed in a boiling water bath canner for less than 10 minutes, once filled, need to be sterilized first by boiling them in hot water for 10 minutes before they’re filled.
- Is it safe to process food in the oven?
No. This can be dangerous because the temperature will vary according to the accuracy of oven regulators and circulation of heat. Dry heat is very slow in penetrating into jars of food. Also, jars explode easily in the oven.
- Can two layers of jars be processed in a canner at one time?
Yes, in either the boiling water bath or pressure canner. Place a small wire rack between the layers so water or steam will circulate around each jar. Make certain that the water covers the tops of all jars by 1 inch in a boiling water bath canner. The pressure canner should have 2 to 3 inches of water in the bottom.
- Is it necessary to exhaust a pressure canner?
Yes, it is very important to allow steam to escape for 10 minutes before closing the valve, or placing the weight on the vent. If the canner is not exhausted, the inside-temperature may not correspond to the pressure on the gauge.
- If I find mold growing inside a jar of canned food, can I just scrape it off and eat the food?
Mold growth in foods can raise the pH of the food. In home canned products, this could mean that the high acid products could become low-acid and therefore run the risk of botulism or other bacterial spoilage. Thus, any home canned product that shows signs of mold growth should be discarded. Even mold on jellied products could be producing a mycotoxin (poisonous substance that could make you sick). USDA and microbiologists recommend against scooping out the mold and using the remaining product.
- Is it safe to can green beans in a boiling water bath if vinegar is used?
No. Recommended processing methods must be used to assure safety. Recommended processing times cannot be shortened if vinegar is used in canning fresh vegetables (this does not refer to pickled vegetables). Green beans should be canned in a pressure canner.
- Should all vegetables be precooked before canning?
For best quality, yes. However, some vegetables can be packed raw or cold into jars before being processed in the pressure canner.
- What vegetables expand instead of shrink during processing?
Corn, peas and lima beans are starchy and expand during processing. They should be packed loosely.
- Can I can my own salsa recipe?
Salsas are usually mixtures of acid and low-acid ingredients; they are an example of an acidified food. The specific recipe, and sometime preparation method, will determine if a salsa can be processed in a boiling water canner of a pressure canner. A process must be scientifically determined for each recipe. Your county Extension agent will have tested recipes for salsas.
- How do I can oil with herbs? Can I can pesto?
Herbs and oils are both low-acid and together could support the growth of disease-causing Clostridium Botulinum bacteria. Oils may be flavored with herbs if they are made up for fresh use, stored in the refrigerator and used within 2 to 3 days. There are no canning recommendations. Fresh herbs must be washed well and dried completely before storing in the oil. The very best sanitation and personal hygiene practices must be used. Pesto is an uncooked seasoned mixture of herbs, usually including fresh basil, and some oil. It may be frozen for long term storage; there are no home canning recommendations.