It can be hard to understand when you start home canning as to what exactly is required to make tomato products safe. Is it salt? Sugar? Are the tomatoes safe on their own, is it how long you boil tomatoes for before putting them in the jar, is it the seal?
How do you make a home canned tomato product safe?
To answer that question, you first have to answer what the ultimate concern is.
The concern is botulism. Yes, it does happen; here are some recent cases of botulism from improperly home canned tomato products.
And botulism spores are the hardest nasty to deal with.
Bizarrely enough, that’s good news in a way. Because preparing a home canned product with botulism spores in mind is the highest bar we have to shoot for, in doing so you just happen to also deal with all the other nasties too and so don’t even need to think about those ones.
To make a home canned tomato product safe from botulism spores springing to life and releasing their toxin inside your jars, you have to either:
- neutralize botulism spores with acid and then process the jar, or,
- kill them off entirely through processing alone.
Anything being water-bath (or steam) canned won’t kill the spores off as it’s not hot enough, so instead you have to make sure you have the right acidity to neutralize them (though you still need to process the jar: we’ll cover that in a bit.)
If you are pressure canning, then the actual tested processing time you are using will kill them off entirely and acidity becomes irrelevant.
Acidifying plain tomato products makes them safe for water bath canning.
It’s not always realistic to do acidify a tomato product though. Sometimes there are so many low-acid ingredients added that you just couldn’t add enough acidity without turning every tomato product into tangy ketchup or relish. Who wants to pour a tomatoey vinegar on their spaghetti? So you pressure can instead.
(To be clear: neutralizing the spores with the acidification process is deemed to be just as safe as pressure canning, so don’t panic and think you should start pressure canning your plain tomato products to be extra safe.)
What type of tomato products get water-bath or steam canned?
Tomato products that are high acid get water-bath or steam canned.
That would be “pure” tomato products such as crushed tomatoes, tomato sauce, whole or chunk tomatoes, tomato paste, etc, to which the correct amount of acid has been added.
It also includes obviously high-acid tomato condiment or speciality products such as ketchup, pickled tomatoes, tomato pie fillings and jams, salsas, tomato relishes and chutneys, etc. In these products the acidity is not just a safety feature, it’s a key component of the character of the product.
Many of those specialty products you would never want to pressure can. No one would want to eat salsa or relish that has been pressure canned; the resulting product would be a horrible moosh.
What type of tomato products get pressure canned?
Tomato products with a lot of low-acid ingredients such as a lot of onion or a lot of celery tend to call for pressure canning. (Note: an exception is Minnesota Mix, specially developed to still be acidic enough for water-bath or steam canning.)
Tomato products with added meat or mushrooms will always call for pressure canning.
Think of an item such as spaghetti sauce. No one in their right mind would ever want to try to acidify a mushroom and meat spaghetti sauce to the point where it was safe for water-bathing: the resulting vinegary product would be unpalatable on pasta, and likely still unsafe.
These products do NOT depend on acidification for safety.
These products will instead have a far longer processing time to actually kill any botulism spores outright, rather than just neutralize them with acid. Any acidity added to the recipe (such as red wine vinegar, etc) will likely be for taste.
Never process tomato sauces with meat or mushrooms in a boiling water bath. Use a pressure canner.”  Penn State Extension. Acidify Tomatoes before Canning. 10 August 2012. Accessed January 2015.
Why though do I have to acidify some pressure canned tomato products anyway?
Some tomato products will give you the choice of either water bathing (or steam canning), or pressure canning, but still require the tomato product to be acidified anyway, even if you do go the pressure canning route.
This is the confusing part, admittedly, until you understand the reasoning.
The reason is that the pressure canner for these acidified tomato products is not being used as a complete and total sterilization tool, as it is for the above unacidified products. Instead, it is being used as a time and energy saver for high-acid items that would otherwise be water-bathed.
The processing times for these “pure” tomato products are actually shorter than they would really need to be if the goal were with them to kill the botulism spores outright through heat. The shorter processing times are completely dependent on the tomatoes having been acidified, which neutralizes botulism spores and prevents them from “germinating.”
Dr Elizabeth Andress of the National Center for Home Food Preservation says,
The USDA process for home canning of tomatoes is only based on it being below a pH of 4.6 or treated as an acid food. Even when we provide a pressure canning alternative in the USDA book it is only the equivalent of a boiling water process. In other words you can use a higher temperature in the canner so you can have a shorter time, it was never developed as a process for pressure canning for elimination of concerns about botulism as if it were a low acid tomato. So that’s why we say you still have to acidify if you use the pressure canning when both are offered, they are only equivalent processes, there is not a separate pressure canning process for controlling botulism in tomatoes that anyone has researched and properly tested.”
Pressure canner times are presented as an equivalent of boiling water treating tomatoes as a low pH, high acid food. The pressure canner recommendations were not developed for treating tomatoes as low acid foods, thus acidification still needed in pressure canning tomatoes. There is no [pure] pressure canner process per se that anyone has researched and tested as of yet. These equivalents were developed by USDA/ Penn State Center for Excellence in the 1980s and are still the current recommendations.”  Andress, Elizabeth. “History, Science and Current Practice in Home Food Preservation.” Webinar. 17:00. 27 February 2013. Accessed January 2015.
In July 2015, the National Center for Home Food Preservation updated its main tomatoes page to emphasize this again, and clear up some confusion that had started to drift about:
If a procedure from the USDA Complete Guide to Home Canning for canning tomatoes offers both boiling water and pressure canning options, all steps in the preparation (“Procedure”) are still required even if the pressure processing option is chosen. This includes acidification. The boiling water and pressure alternatives are equal processes with different time/temperature combinations calculated for these products. The pressure processing options in these products were not developed for tomatoes without added acid.” National Center for Home Food Preservation. Selecting, Preparing and Canning Tomatoes. Reviewed July 2015. Accessed June 2016.
All pressure canning times for plain tomato products were developed by the USDA, so whenever you see directions for pressure canning such products, Ball, Bernardin or wherever, they are based on that research.
Note that this speed-up process for “pure-tomato” products can only be used when a pressure canning processing time and pressure is given.
What’s better, water bathing (steam canning) or pressure canning?
To be clear, these options are only possible when your tested recipe gives them to you.
Steam canning is usually always fastest as a process overall, when water bathing (which it’s an equivalent to) is a choice.
That being said, see discussion here.
So salt isn’t need to make my tomato products safe?
Salt plays 0 — zero, as in zippity doo dah — role in the safety of those products.
Barb Ingham at the University of Wisconsin Extension says,
You may safely reduce or eliminate salt in all home canned tomato recipes.” Ingham, Barbara. Home Canning: Can I Make Substitutions Safely? University of Wisconsin Extension. 23 June 2015. Accessed June 2016 at https://bayfield.uwex.edu/2015/06/23/play-it-safe-changes-and-substitutions-to-home-food-processing-recipes.
If I acidified my tomato sauce, why do I still have to process the jar?
Many moulds are also resistant – note how many unprocessed jars of “high-acid” jams go mouldy. Moulds grow seen and unseen, and when they do, they lower the acidity. Lower the acidity level enough, and the botulism spores that had been held neutralized by it can now spring to life.
Consequently, modern canning of water-bathed tomato products employs the dual process of acidity and processing to ensure a safe, quality product
The processing ensures that no mould spores can play a helping hand to botulism spores.
Incidentally, there are some other nasties that also don’t mind acidity. Some strains of listeria and salmonella have been noted in labs to be resistant at times to acidity.
But in processing the jar to kill off any mould spores that might aid botulism spores, they are also killed off.
See how treating for the “big B” really does take care of everything?
Someone on the Internet said all this fuss with tomatoes was unnecessary
Just “bottling” tomatoes without processing the sealed jars killed two people in 1974.
…early in 1974 there were two deaths from botulism poisoning traced directly to home-canned tomatoes and tomato juice…. Meanwhile the public health officers discovered what actually allowed the spores of C. botulinum to make the toxin that killed the victims. Common bacteria or molds grew in the food in the jars and thereby reduced the acidity because the natural acid in the tomatoes was metabolized by the micro-organisms as they grew and developed. It was established after compassionate, but thorough, investigation that these bacteria or molds survived either because the tomatoes were canned by the discredited open-kettle method, or entered under the lid of a jar that wasn’t adequately sealed. Inadequate processing is virtually always the cause of food poisoning that develops during shelf life.”  Hertzberg, Ruth; Greene, Janet; Vaughan, Beatrice (2010-05-25). Putting Food By: Fifth Edition (p. 119-120). Penguin Publishing Group. Kindle Edition.
In 1999, an unprocessed jar of tomatoes sent six people in Toronto, Canada to the hospital with botulism, including a visiting parish priest from Italy.  BC Centre for Disease Control. Botulism in British Columbia: The RISK of Home-Canned Products. January 2015.
Home canning safe, quality ,healthy tomato products really is very easy now.
They’ve got the science all worked out.
Just follow a tested recipe or procedure from a reputable source.
There are enough tested recipes for canning tomatoes to keep you hopping for the next five years if you start trying to work through them now.
So don’t worry: you know now what the issues are, and how they are dealt with. So relax and get busy!
Browse site on all tomato canning topics
References [ + ]
|1.||↑||Penn State Extension. Acidify Tomatoes before Canning. 10 August 2012. Accessed January 2015.|
|2.||↑||Andress, Elizabeth. “History, Science and Current Practice in Home Food Preservation.” Webinar. 17:00. 27 February 2013. Accessed January 2015.|
|3.||↑||National Center for Home Food Preservation. Selecting, Preparing and Canning Tomatoes. Reviewed July 2015. Accessed June 2016.|
|4.||↑||Ingham, Barbara. Home Canning: Can I Make Substitutions Safely? University of Wisconsin Extension. 23 June 2015. Accessed June 2016 at https://bayfield.uwex.edu/2015/06/23/play-it-safe-changes-and-substitutions-to-home-food-processing-recipes.|
|5.||↑||Hertzberg, Ruth; Greene, Janet; Vaughan, Beatrice (2010-05-25). Putting Food By: Fifth Edition (p. 119-120). Penguin Publishing Group. Kindle Edition.|
|6.||↑||BC Centre for Disease Control. Botulism in British Columbia: The RISK of Home-Canned Products. January 2015.|