Saturday, September 10, 2011
To clarify: canning relies on two things to preseve foods safely: heat and acidity.
Tomatoes are an acid food* and therefore can safely be canned in a water bath canner. Beans, peas and corn are low acid, and therefore must be canned in a pressure canner, which achieves much higher temperatures.
Salsa falls somewhere in between...Tomatoes are acidic, but the onions, peppers and garlic are not, so the safest way to process the salsa is to add lots of vinegar to really crank up the acidity.
* Some of the newer tomato varieties have been designed for a lower acid content to make them more digestible. So you cannot even trust that all tomato varieties are safely canned by the water bath process. So if you do make salsa, I advise you to pack it into wide mouth CAN OR FREEZE jars and freeze it. And if you want to make sauce, I advise you to freeze that too... see Freezer Tomato Sauce.