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Canning Tomatoes: Acidity and Other Concerns

| 9/11/2012 12:41:49 PM

Tomato Canning Tips

All around the country, this summer’s tomato crop is outstanding. This will likely lead to more canning of these garden yummies. While canned tomatoes on the shelf is a comforting sight, a few words of canning caution are still worthwhile.

A recent article on this site discussed the safety of old canning recipes and techniques. One of the main reasons why “Grandma’s Favorite” or recipes older than about five years shouldn’t be used is that chemical changes have occurred due to newer vegetable varieties being developed, particularly in tomatoes. Many varieties have lost their acidity through modern genetic tweaking and hybridizing. So, it’s necessary to add acid to tomatoes — including heirloom varieties — when canning them. Lemon juice is considered adequate and effective for this purpose and must always be used for water-bath and steam-pressure canning.

If you forget to add lemon juice, you’ll be in trouble. This was a hard lesson learned by one of my master gardener colleagues. During the prior day, she had harvested her crop and processed some dozen or more jars of tomatoes to be used for making sauce. Then she telephoned me in a panic, saying that she just realized she’d forgotten to add lemon juice due to a distraction. 

The jars had all gone through the prescribed canning cycle, had sealed correctly, etc. “Are these going to be okay?” she asked.  

I told her it was too bad that she hadn’t realized the lemon juice omission immediately after the jars had come out of the canner. If she had, she could have opened all the jars, dumped the contents into a pot, reheated the tomatoes, and added lemon juice to each jar as she filled it. Then, she could have put the tomatoes through the canning cycle again, using fresh lids.  

8/13/2017 7:56:22 PM

My parents have canned tomatoes for 17 years and have never used lemon juice or citric acid, just salt and they have never had a problem. They bring the peeled and cored tomatoes to a boil first then add them to hot jars and process in water bath.

Erin Antel
9/21/2012 3:55:04 PM

I canned tomatoes for the very first time this year and was so proud of myself. Tomatoes are just about the only canned food I buy from the store, but I want to stop because of BPA concerns. (Also, I like doing things myself!) Ironically, now I am plagued with a different set of concerns. A couple of times I forgot the lemon juice. Luckily, I remembered as soon as I put the lid on and before I processed, so I took the lid off, added it and put a lid and processed it. But those couple of times have me worrying if there were any that I forget and didn't catch. Then I was so worried that I would under process them, so I over processed them by about double the time. The very first batch actually boiled down so that the jars were only half covered by water. And in all of my jars, the tomatoes floated to the top and the liquid went to the bottom. My husband's grandmother canned for years and I asked her about all of this. She assured me that they were all fine as long as the cans sealed, which they all did (they all "pinged" and I can pick up all of they by the lids and they remain sealed.) However, grandma also talked about canning corn in a waterbath, so I wasn't as reassured as I wanted to be. So to end a very long story (sorry!), I am scared to use my canned tomatoes! What if I did something really wrong? What if I poison my kids? Should I throw it all away?

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