OpenKettle and Water bath canning are safe for vegetables and fruits with a high acid content (4.6 pH or lower). Both openkettle and water bath canning reach a maximum of 212 degrees, which is enough to kill the molds and yeast that commonly grow in acidic foods. Active bacteria is also killed by cooking at 212 degrees for a minimum of 15 minutes, but Botulism bacteria spores (dormant seeds) can withstand this temperature. Botulism bacteria spores can lie dormant until they are in a low oxygen, low acid environment; At such time they can become active and multiply, but the bacteria that causes Botulism, Clostridium botulinum, does not grow in high acid environments.

According to the CDC: "Botulism is a rare but serious illness caused by a nerve toxin that is produced by the bacterium, Clostridium botulinum." The bacteria is naturally found in soil and thrives in a low oxygen environment. This means the bacteria can grow in low acid foods (higher than 4.6 pH) in sealed containers, without the presence of air. Therefore, low acid foods must be processed with a pressure canner.

If in doubt if your tomatoes are acidic enough, add 1/8 to 1/2 tsp citric acid to each quart, or 12 tbsp bottled lemon juice.

Please note: When testing food, spoon a small portion into a separate container for testing and discard that test sample when finished. The test strips may contain chemicals that could be harmful if ingested and even small amounts are not recommended.