Home-canned tomatoes are one of my must-have staples.
It’s very hard to find store-bought canned tomatoes and tomato sauce in glass jars… yet due to their acidity, that’s a biggie for me. I try to stay away from metal as much as possible.
How To Safely Can Tomatoes
When it comes to canning tomatoes at home, there’s a few things you must know in order to ensure your home-canned tomato products are safe and don’t come with a side of botulism.
First, never can tomatoes that have been through a frost. Frost significantly lowers acidity, so these tomatoes are not considered safe for canning.
Second, although tomatoes are considered an acidic food, their pH must be 4.6 or lower to be safe for water bath canning. Because they are technically a fruit, we are able to water bath can tomatoes. (All vegetables, unless pickled, must be pressure canned to avoid botulism.)
And yet…
Tomatoes aren’t as low on the pH scale as some people think.
The Myth About Heirlooms & Acidity
Tomatoes are borderline — falling between a 4.30 and 4.90 on the pH scale (source).
Many people falsely believe that an heirloom tomato is more acidic, so if they’re growing and using heirloom tomatoes, they don’t need to add additional acid.
Testing has confirmed that this is not the case. In fact, some heirloom varieties aren’t as acidic as hybrids. Don’t rely on the type of tomato as your guide for its acid content.
All home-canned tomatoes, including tomato sauce, tomato juice, and tomato paste should have a form of acid added to them — even when pressure canned. The tested times and recipes for pressure canned tomatoes are with added acid, not without.
Types Of Acid For Home-Canned Tomatoes
There are 3 types of acid to add to your home-canned tomatoes. No matter which acid you choose, it should be added to each individual jar to ensure proper acidity.
The 3 types of acid for home-canned tomatoes are:
- Citric acid
- Bottled lemon juice (not fresh because acidity varies on how the lemon is grown and harvested)
- Vinegar (not homemade vinegar — it must be 5% acidity)
Most people choose not to use vinegar for taste reasons.
Add the chosen acid to the jar before filling with tomatoes to ensure each jar has the proper amount.
- Citric acid: ¼ teaspoon per pint jar and ½ teaspoon per quart
- Bottled lemon juice: 1 tablespoon per pint and 2 tablespoons per quart.
- Vinegar: 2 tablespoons per pint and 4 tablespoons per quart
Home-canned tomatoes are a wonderful addition to your pantry because lycopene, an antioxidant, increases in bioavailability when tomatoes are cooked (source). Sweet, right?
Personally, I love to can tomato sauce. It’s so versatile! With home-canned tomato sauce, I then make tomato paste, spaghetti sauce, pizza sauce, or I add it to stews or soups for more flavor.
Do you can tomatoes? Do you use a water bath or pressure can them? Which acid do you prefer?
This post was featured in How to Can Tomatoes 16 Ways.
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I use water bath system,glass jars and my own tomatoes. I prefer lemon juice as an acid. We live in easter Ontario Canada on the
st Lawrence river across form NY State. This yr every thing is late because we have had record rain! My tom’s are just now beginning to grow. So i will probably have to use green house tom’s this year. We can whole tom’s,crushed, and juice, both plain and spiced. I also make my own hot sauce, mild, hot and suicide.
Thank you! We are planning to can catch-up this week, and this will be a big help.
Oops. That should read ketchup.
Italians have been making and bottling tomatoes for generations and we have never used any sort of acid, we keep or sauce for years and never had a problem! Just confused as to why acid has to be added. We first boil our tomatoes, then we bottle them in glass bottles and then boil the sauce in the glass bottles. Surely this should be enough to preserve and not produce any bacteria etc! Would love to have one of my stored bottles tested.
Angela,
Unfortunately, due to testing and as I mentioned above in the article with the acid ph levels of tomatoes and avoiding botulism, you’re taking a big risk. Because botulism is a toxin that is fatal, I personally don’t take a change when I know it’s a risk.
I guess I break all the rules. I chop the tomatoes and simmer them until there is enough liquid to cover the solid chunks. Then I put them into canning jars and process them dry in a 250 degree oven. If I add less acidic vegetables to the mix, as in making chili or salsa, I will also add lemon or lime juice. I have been doing it that way for almost thirty years and never had a problem. Have I just been lucky? I don’t know. Maybe I should start testing the pH of things I can.
I would highly recommend attending the class Wardee and I are hosting this Tuesday on canning safety so you can understand the science behind why that is a dangerous practice. I’m very grateful you haven’t had a problem but you’re taking a big risk there.
https://melissaknorris.lpages.co/homecanningwebinarwardeh/
I have been canning tomatoes, tomato juice and tomato sauce for years. I learned from my mother many years ago and she taught me to always add lemon juice and a little salt. So, I have always added acid.
A couple of years ago when I put up over 250 jars of tomato products, I figured out an easier method for juice-I just mix any kind, including cherry varieties (Sungolds make a lovely yellow tomato juice) and for sauce-some sort of Roma variety. I wash my tomatoes well, quarter them and pop them into my Vitamix, skins, seeds and all. After blending them, I cook them down to the consistency I want, put into jars with lemon and Himalayan or sea salt and then water bath them. This has hours and hours out of canning time for me. No more scadling, peeling or squishing through a colander.
Jan, thanks so much for sharing and I’m so happy your mom knew the importance of adding acid to stay safe with your home canned jars of wonderfulness.
Yikes! I hate typos! Please add “saved” before hours and hours and change scadling to scalding! LOL!
I have never added acid to my tomatoes and all I have is a waterbath canner. I used to stuff jars with cut up tomatoes add oregano, salt, onion and garlic and can. Makes for a great tomato salad on the go! Never had issues with my unacidified waterbath canned tomatoes -just lucky?
On the safety note, I read that home canned pumpkin butter is also not safe when it comes to botulism. However I bake my pumpkin halves @350 F for about one hour, that should kill all botulinum toxins.
GB, adding onion and garlic without acid is a huge risk because they’re both non-acidic and should be pressured can. I would say luck with God’s grace. You might want to attend this home canning safety class Wardee and I are holding https://melissaknorris.lpages.co/homecanningwebinarwardeh/
And baking pumpkin is not the same as pressure canning, dry and wet heat are very different beasts. You may safely pressure can pumpkin when it is cubed, but not ever in a puree form and then only following the pounds per pressure and full time.
I wanted to make pumpkin butter and every where I looked said it was not safe unless you use pumpkin puree from a commercial can. But if you bake at 350 F and then make pumpkin butter….. I had tons of pumpkins that one year, wanted to make butter as well. I freeze most of my pumpkin for baking, never canned any.
I always scald my tomatoes, peel them, and pack them in quart jars with a tsp of salt. I don’t add any liquid and pressure them at 11 lbs pressure for 25 minutes. Never had any problem. Is this safe?
My parents always scalded their tomatoes, peeled them and quartered them put them in a pan and brought to a boil and boiled them 20 mins. Jarred them with a tsp of salt never had a problem. Is this safe?
I canned whole tomatoes first time this year my recipe did not say to ad an acid. I did not, how do I know if they have botulism?
When I learned to can tomatoes, we never added anything but salt, but that was a very long time ago. Since then, tomatoes have been bred to be less acidic. Most store bought tomatoes aren’t acid enough, and garden tomatoes are iffy. I use a good quality red wine vinegar when I can find it at %5 or higher. My Mom used it for any Italian dish she made, gives the sauce a mild wine flavor. When I’m doing chopped tomatoes, I use citric acid, I don’t like the way the lemon tastes in my tomatoes,