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Acidity and canning tomatoes

Basket of tomatoes

Cooking tomatoesWhen hot water bath canning, it's important to pay attention to everything that goes in the jar.  Sweeteners like honey and sugar can be added with impunity, but including basil and onions in a tomato sauce will raise the pH so much that you'd have to pressure can.  To stay on the safe side, look for proven recipes or simply can pure fruits or tomatoes.

While I'm on the topic of acidity, I should mention that the acidity levels of tomatoes may sometimes be too low for hot water bath canning unless you add a bit of bottled (not fresh) lemon juice or citric acid.  The magic cutoff point is 4.6 --- tomatoes with a pH at or above this pH are not safe to hot water bath can on their own.  Proven tomatoes that definitely need lemon juice added include:

Ace, Ace 55VF, Beefmaster Hybrid, Big Early Hybrid, Big Girl, Big Set, Burpee VF Hybrid, Cal Ace, Delicious, Fireball, Garden State, Royal Chico.

Hot water bath canning tomatoesDepending on who you talk to, San Marzano tomatoes may or may not be safe. 

Varieties that definitely have a pH low enough to allow you to hot water bath can them without adding any lemon juice or citric acid include:

Abraham Lincoln, Amana Orange, Anna Banana, Antique Roman,  Aunt Ruby's German Green, Beefsteak Extra Large, Big Rainbow, Bisignano #2, Black, Black from Tula, Black Krim, Burpees Delicious, Caspian Pink, Cherokee Purple, Climbing Trip L Crop, Costoluto Fiorentino, Costoluto Genovese, Currant Tuscan Bombolino, Ernie's Plump, Evergreen, Giant Syrian, Goliath, Grappoli D'Inverno, Hillbilly, Howard German, Italian Giant Beefsteak, Italian Heirloom, Italian Plum Canning, Ingegnoli Gigante Liscio, Joe's Plum, Jubilee, Kellog's Breakfast, Kootenai, Large Polish Paste, Laurano, Le Case Di Apulia, Lilians Yellow Heirloom, Long Keeper, Lycoperscon Cheesemanii, Marglobe, Moskvitch, Mortgage Lifter, Mr. Stripey, Napoli, Nebraska Wedding, New Hampshire, New Jersey, Opalka, Oregon Spring, Oscar, Pantano Romanesco, Persimmon, Pink Brandywine, Platillo, Polish Giant, Pomadoro Grosso, Prairie Fire, Rutgers, Principe Borghese, Red Brandywine, Riesentraube, Rio de Fuego, Rio Grande, Roman Candle, San Marzano (listed by some as being above), Santiam, Saucy, Silvery Fir Tree, Siletz, Soldacki, Stupice, Super Italian Plum, Super Sioux, Striped Stuffer, Tondino Di Manduria, Tyboroski, Yellow Brandywine, Yellow Pear, Yellow Perfection, Watermelon Beefsteak, Zebra, Zogola

Adding lemon juice to canned tomatoesHowever, to make the decision even more complex, a high acid tomato variety may produce low acid tomatoes if the fruits are overripe, bruised, cracked, affected by blossom end rot, or nibbled by insects.  In addition, tomatoes ripened off the vine, in the fall when days are shorter, in the shade, or on dead vines can all have a pH too high to allow hot water bath canning without added lemon juice.  To play it safe, you might as well add the lemon juice recommended in most modern recipes (2 tablespoons per quart of crushed tomatoes.)

To read more, check out Weekend Homesteader: September on Amazon (or email and ask for your free pdf copy.)  Thank you to everyone who has already given the ebook a try, and I would be eternally grateful to anyone who takes the time to leave a review!

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Please forgive me, but I'm confused. I honestly know nothing about canning (though I'd like to learn), but your comment has me confused...

"While I'm on the topic of acidity, I should mention that the acidity levels of tomatoes may sometimes be too high for hot water bath canning unless you add a bit of bottled (not fresh) lemon juice or citric acid."

So, you cure the problem on high acidity in tomatoes for canning by.... adding more acid?

Comment by Shannon Thu Sep 1 19:58:21 2011
No, you're totally right! That's a typo --- I should have said the pH was too high (or the acidity was too low.) Thanks for catching that!
Comment by anna Thu Sep 1 20:34:09 2011
I thought that might be what had happened. After all, it does get confusing when talking about acidity and pH since HIGH acid = LOW pH. Glad I wasn't missing something... :D
Comment by Shannon Thu Sep 1 22:06:59 2011

One very unique homestead, $1,500 per acre, the opportunity of a lifetime