I have a recipe for canning balsamic caramelized onions. The recipe calls for 2 lb of onions and 3/4 of a cup of balsamic vinegar and 3/4 of a cup of sugar. That's it. The onions would be caramelized in a slow cooker without using any fat. I have seen the exact same recipe water bath canned and pressure canned. So I am confused. I know that onions need to be pressure canned but I'm wondering if the balsamic vinegar is enough of an acid to water bath can them. Thank you.
Thank you for the question. Because onions are a low acid vegetable they must be pressure canned to prevent botulism. Here is a link about pressure canning onions:
This is regardless of the addition of vinegar.
In addition, it is recommended to follow only safety tested recipes. The above link includes a recipe for pressure canning onions.
Another great reference online is the National Center for Home Food Preservation
Here is a link: https://nchfp.uga.edu/