How to Can Tomatoes Safely

The Safety Issues around Canning Tomatoes and Tomato Products

I stopped in at CTV Morning Live to chat about how to can tomatoes safely.  This article provides a little more info on why canning tomatoes is a little more tricky than other fruits.

tomatoes - watermarked

Tomatoes are Borderline between High Acid and Low Acid

The issue with canning tomatoes is that the level of acid in tomatoes varies with a pH range of 4.4 to 4.9.  Even though they may taste acidic to us, tomatoes are less acidic than most fruit, for example apples range in pH 3.2 to 4.0.
Remember high acid=low pH and that only high acid foods with a pH of 4.6 or lower can be safely water bath canned. That means a lot of tomatoes can’t just be canned as is. We need to add acid to safely can tomatoes.
Waterbath canning requires pH ≤ 4.6,
tomatoes’ pH is 4.4 to 4.9. Be safe add acid! 

A tomato’s acid level changes as it grows and may differ from one year to another due to growing conditions. In other words, there’s really no way for us home canners to know what the acid level of our tomatoes is at the time of processing. But that’s okay, we can accommodate for this uncertainty by adding lemon juice, vinegar or citric acid (a powdered product you can get at the pharmacy) to our tomatoes. By doing so, we know for certain that the pH will be where it needs to be.

Add 2 Tbsp lemon juice to each Quart jar when canning tomatoes. 
I’ve never tried citric acid, but I’ve read that it leaves little or no taste to the final product. If you don’t want to change the flavor profile of your canned tomatoes, this is an ideal solution.
I prefer the taste of lemon juice over vinegar, so that is what I have always used. When it comes to canning, use commercial lemon juice as opposed to fresh squeezed lemon juice. Again, because of varying growing and storage conditions, knowing the exact acidity of a lemon is difficult at home. To be sure you’re getting the right level of acidity, it’s best to use commercial lemon juice.
canning tomatoes safely

Clostridium Botulinum

One of the most dangerous pathogens and one we want to avoid in home canning is Clostridium botulinum, the bacteria that causes botulism and it can be fatal (read more here).  This bacteria thrives in high moisture, low acid, low salt and low oxygen environments.  Canned tomatoes, tomato products, meat, soups, stews, fish, beans and other low acid foods provide the ideal environment for botulism spores. Only by processing foods according to current tested, recommended practices can we ensure that every can is safe.
The threat is real! Not every can that is processed using old, traditional methods may lead to botulism or food poisoning – but the risk is there and it’s very real. It is impossible to tell if  Clostridium Botulinum is present, so ALL low acid foods must be processed safely. Even frozen vegetables can have Clostridium botulinum present as was the case in a recent botulism outbreak after improperly canning frozen commercial peas 2018 Botulism from canning frozen peas. In the 2018 pea incident, 3 ladies ended up in hospital and had to be intubated to enable them to breath, luckily they recovered. Sadly a 2015 church potluck in Ohio is evidence that home canned goods processed incorrectly can cause tragedy. Ohio Church Potluck Botulism Outbreak turns fatal. 

How to avoid Clostridium Botulinum in Home Canned Goods

– use high acid foods
– add acid (follow tested recipes to ensure the correct amount, see National Centre for Home Food Preservation)
– heat process low acid veggies, meats and other canned goods in a pressure canner where temperatures can get to the required 240°F/116°C and process it for the recommended time.  Again, it’s important to follow the recommended times provided by tested recipes from a trusted source like the National Centre for Home Food Preservation
Canned tomatoes are a great addition to any pantry and by following current practices, you can rest easy knowing you’ve done your best to ensure a safe and delicious product.
Other tomato posts you’ll find on this website:
Canning Posts include:
Want to learn more? How about a preserving workshop with Getty? Call today as fall dates are booking quickly. Getty Stewart is an engaging speaker and writer providing tasty recipes, time-saving tips, and helpful kitchen ideas to make home cooking easy and enjoyable. She is a Professional Home Economist, author of Manitoba’s best-selling Prairie Fruit Cookbook, Founder of Fruit Share, mom and veggie gardener.

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2 Comments

  1. Do i need to to add acid when making hot sauce with tomatoes from the garden? Also what about when making marinara sauce?

    1. Hi Summer,
      If you plan to can any kind of tomato product using the hot water bath technique (versus pressure canning) then YES, you need to add acid. The exact quantities will vary depending on the other ingredients in your recipe. Your safest route is to follow a recipe that’s been tested by a credible source like the National Centre for Home Food Preservation (http://nchfp.uga.edu/) or Bernardin (http://www.bernardin.ca/). Better safe than sorry!
      Getty

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