Canning low-acid tomatoes safely requires adding acid before processing to ensure proper acidity levels.
When canning tomatoes, especially varieties that are naturally low in acid, it is crucial to increase the acidity to prevent the growth of harmful bacteria like Clostridium botulinum. Adding acid before processing is a standard and recommended practice for safe home canning of tomatoes.
Why Add Acid When Canning Tomatoes?
Tomatoes were once considered sufficiently acidic for water bath canning. However, with the development of new, less acidic varieties and variations in ripeness and growing conditions, relying solely on the tomato's natural acidity is no longer considered safe by current home canning guidelines.
To ensure a safe acidity level, add bottled lemon juice or citric acid to each jar before processing. This step lowers the pH of the tomatoes, creating an environment where dangerous bacteria cannot survive or produce toxins during storage.
How to Add Acid to Tomato Jars
The reference provides specific amounts for adding bottled lemon juice or citric acid. It's important to use bottled lemon juice, as its acidity is consistent and standardized, unlike fresh lemon juice which can vary.
Here are the recommended amounts based on jar size:
- Quart Jars: Add 2 tablespoons bottled lemon juice OR ½ teaspoon citric acid crystals.
- Pint Jars: Add half the amount used for quart jars. This means adding 1 tablespoon bottled lemon juice OR ¼ teaspoon citric acid crystals.
Place the required amount of bottled lemon juice or citric acid crystals in the bottom of each jar before filling it with your prepared tomato product (whole, crushed, juice, etc.).
Acid Additive Amounts
| Jar Size | Bottled Lemon Juice | Citric Acid Crystals |
|---|---|---|
| Quart | 2 tablespoons | ½ teaspoon |
| Pint | 1 tablespoon | ¼ teaspoon |
Note: Always use bottled lemon juice for canning due to its consistent acidity.
After adding the acid and filling the jars with your hot tomato product, process them according to tested and approved canning recipes. Processing time and method (water bath or pressure canning) will depend on the specific tomato product, altitude, and chosen canning method. Following research-based canning guidelines ensures the safety and quality of your canned goods.
Adding this required acid ensures that even low-acid varieties are safe for shelf storage after proper heat processing.
