Questions to ask before trying a canning recipe

  • vegetables and canned vegetables

The University of New Hampshire Cooperative Extension recommends following home canning recipes and guidelines that have been tested by scientific research. This ensures a safe, quality product. Here are some questions to ask when searching the Internet for home canning recipes and guidelines.

  • Was the recipe handed down through the generations? Some generational recipes and processes were developed by trial and error but were not necessarily research tested. Think about who deemed it safe through trial and error.

  • Was the recipe made up, rather than tested? Time and effort go into testing a recipe so that the right portion of vegetables and/or protein and/or acids are considered for acidity. Acidity levels determine if the product needs to be canned by boiling water or pressure. Without scientific testing, you do not know the acidity level, how long the product needs to be processed or by which method to be safe.

  • Does the recipe not call for processing jars of hot jams, pickles and relishes? Some people assume that if the jar seals, it is safe to consume. However, it is not acceptable to pour hot jam, pickles and relishes into jars and just wait for the seal to form. Through research, we know that these products need to be processed in boiling water or an atmospheric steam canner to destroy microorganisms that can cause spoilage in the headspace and to create a strong vacuum seal.

  • Do the directions say to add extra starch, flour or other thickener to a recipe? This will slow the rate of heat penetration into the product and can result in under processing. The result could lead to botulism, a potentially deadly foodborne illness that can be caused by improper canning methods. Each recipe is tested so that all products in the jar reach a certain temperature for a certain amount of time to destroy microorganisms. This ensures that the jar of food is safe to consume. It is not safe to just add minutes to the processing time.

  • Does the recipe call for adding EXTRA onions, chilies, bell peppers or other vegetables to salsas that will be canned? These extra vegetables can lower the acidity level of the salsa and can result in botulism. Some salsa recipes allow the exchange of some of the hot peppers with bell peppers to reduce the spiciness. If it does, then follow the directions exactly.

  • Does the recipe call for boiling water processing for low acid vegetables? Plain and simple, doing this can result in botulism. Pressure canning processes jars of food at 240°F for a recommended time that is adequate to destroy clostridium botulinum spores that cause botulism.

  • Does the recipe lack recommendation for acidifying tomatoes? Not all tomatoes have adequate acidity levels, especially tomatoes that have been harvested from dead vines. Not acidifying tomatoes could result in botulism. The recommendation is 2 tablespoons of bottled lemon juice or ½ teaspoon of citric acid per quart jar while each pint jar can be acidified with 1 tablespoon of bottled lemon juice or ¼ teaspoon of citric acid.

Use research-based recipes from sources that are recent and no earlier than 1994. There have not been major updates since 1994, but there are some new research discoveries. Some of those new discoveries include recommendations like not to can elderberries or white peaches because of safety concerns. The best advice is to use the most recent USDA, National Center for Home Food Preservation or any University Extension recipes and guidelines. In addition, not all recent canning books are research-based. Consider the source and question whether they have tested the recipes to ensure their safety.

The guidelines for safe home canning are not that difficult to follow. Just make certain you use research-based, up-to-date recipes and guidelines, follow the recipe exactly and make altitude adjustments for time or pressure. If you have questions about the safety of your home canning process, contact the UNH Extension Education Center.


National Center for Home Food Preservation (2023). Frequently Asked Canning Questions. University of Georgia.

Riggs, Kathleen (2023). Avoiding Common Canning Mistakes. Utah State University.

Zepp, Martha (2022 September 29). Update Canning Recipes. Penn State University.


If you have questions about canning or food safety, please reach out to Ann Hamilton or Sean O'Brien.

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Food Safety Field Specialist
Extension Field Specialist, Food Safety
Phone: (603) 447-3834
Office: Cooperative Extension, Taylor Hall, Durham, NH 03824