One tablespoon bottled lemon juice = 1/4 teaspoon citric acid
When one is canning something in a boiling water bath, it is vital that that product be high in acid. The reason is that the presence of a concentrated amount of acid is what inhibits botulism spores from germinating into toxin. Many of the fruits we turn into jam are already high enough in acid on their own to be safe for canning, but on occasion we work with items that need some help in the acid department.
Tomatoes are a prime example of a fruit that is needs to be acidified. Depending on the variety of tomato, they can sometimes have a pH (how we judge acid content) that is too high (the pH of the product need to below 4.6) and so that tomato product needs additional acid. Because most home canners aren’t working with a pH meter, it’s recommended that all tomatoes receive additional acid, because it’s impossible to judge acid content based on taste or appearance.
This is why tomato recipes typically call for the addition of either bottled lemon juice or citric acid. Both products deliver a reliable dose of acid that, when added in the recommended amount, ensures that the product is safe for a trip through the boiling water bath canner.
When I write recipes that need acidification, I typically default to bottled lemon juice because I believe it to be a more readily available product (and if you’re curious why it’s bottled lemon juice and not fresh, read this post). However, when I’m making a product that has spent a goodly amount of time cooking down, I will often use citric acid. It comes in powdered form and so doesn’t introduce more liquid that I will then need to reduce.
However, either can be used and they can easily be exchanged one for another. One tablespoon of bottled lemon juice is equal to 1/4 teaspoon citric acid. This means that if a recipe instructs you to add 2 tablespoons of bottled lemon juice to each quart jar before canning, you can easily swap in 1/2 teaspoon of citric acid.
One tablespoon bottled lemon juice = 1/4 teaspoon citric acid
