I often cringe when I see pickling recipes on the internet, but canned tomato recipes are usually downright unsafe. I’m not a complete preservation safety cop, but there are some basic rules I really do follow. I carefully consider the surfaces that encourage microbial growth. I’m kind of a cleaning maniac when I’m canning — I really do scrub up everything and sanitize my sponges before canning. And I make those little suckers feel very uncomfortable by changing their happy low-acid free love festival to a high-acid paranoid police state. Kills the ambiance, you know?
I pay more attention to acid than a Berkeley undergrad. Tomato preparations need added acid because they’re right on the cusp of what we call high and low acid foods on the pH scale. My guess is that those watery plum tomatoes we buy by the lug are on the low end. Low-acid foods are breeding grounds for pathogens, including the dreaded clostridium botulinum. We want to make anything we can either high in acid or high in sugar, sometimes both.
So we add acid. You can play a bit with tastes. Sometimes lemon and lime juice can be used, or vinegars with different flavor profiles, as long as they have 5% acetic acid. But here’s the key:
It’s ok to substitute equal amounts of bottled lemon juice for vinegar in recipes
using vinegar. DO NOT substitute vinegar for lemon juice. Lemon juice is more acidic.
Use only bottled lemon and lime juice in tomato canning recipes. I know, bottled lime is not the best taste and often contains preservatives, but you won’t be able to taste the bottled-ness in your tomatoes, and the preservatives actually may help. The problem is that the acidity of lemons and limes varies over the season, and you want consistency in canning tomatoes, especially if you are using a tested recipe…or if you aren’t using one, you’ll need all the acidity you can get. I save my fresh lemons for high-acid fruit jams, where you can really taste the difference.
Vinegars can pose a different problem. Most of the vinegar one can buy in bulk sizes is standard, commercial stuff with a big 5% printed on the jug. This 5% is not the pH level, it is the percentage of acetic acid in the vinegar solution (the rest is water). White distilled, cider, white wine, and red wine vinegars are most often sold at 5% acid. European vinegars, however, including white and red wine vinegar I often buy for salads, can vary from 3 – 8%. (Compare my “Ac. 8˚” imported Spanish sherry vinegar and the 5% white wine vinegar, above.) Japanese rice vinegar is most often only 3-4.2%, so you shouldn’t use it for canning. The lower amount of acid actually makes for a smoother taste with less bite — great for some dishes, but not great for your shelf-stable tomatoes . In short:
The percentage of acetic acid in vinegar is almost always printed on the bottle, so check it out, and don’t use anything under 5%.
If you follow these two basic rules, you’re on your way to canned tomato nirvana. Turn on, tune in, and drop out, man.