Why old time recipes can't be used for canning
The Question: People have been canning for a long time and it appears that not too many people died from it. Why can't the old time recipes be used? If the recipes were passed down from generation to generation or were published by Mason Jars and companies that made canners, why can't they still be used? Is it all right if someone asks me during one of my presentations if they can make an old time recipe for me to tell them to freeze it instead of canning?
Freezing old time recipes is a good idea—no unique safety issues are associated with freezing.
We recognize that some folks will continue to use old or unsafe methods regardless of Clemson Extension’s recommendations to the contrary. Spores of the organism that causes botulism are present in most foods. I personally am not willing to play Russian roulette with my canned foods or to recommend playing it to others.
Several factors contribute to older, previously recommended recipes now being considered unsafe. Re-tests of some previously recommended processes using the best scientific methods indicated that the process did not reach the temperature to the botulism-causing spores throughout the jars. Some re-tests indicated that the same final temperature was not reached in all jars; thus the heat process was not reproducible. We now know that following these previously recommended processes is risky; Clemson Extension cannot recommend a process that has been found to be inadequate or that cannot be reproduced reliably.
Eating preferences also have changed. More folks like foods that are cooked less and it is more common for canned foods not to be reheated. The botulism toxin is destroyed by boiling for 10 minutes. Boiling a low-acid canned food before eating provides an additional safety measure but longer cooking times are less commonly used.
Some foods have changed over time. For example, tomato varieties have been bred for ease in harvesting; as a result many now have milder flavor and lower acidity than the ancestral tomatoes. Testing has shown that some current tomato varieties have pH values at or above 4.6; a few have pH values of 5 or even greater. But adding the recommended amount of lemon juice lowers the pH of all tested varieties enough to allow for safe water bath canning. That is why acidifying tomatoes is now recommended; it allows for safe processing in a boiling water bath canner.
For multiple reasons, old-time recipes may not be considered safe for canning. Clemson Extension recommends only currently tested and scientifically validated recipes.