Processing High-Acid Foods
Food that has enough acidity to keep the pH of the product below 4.6 can be processed in a water-bath canner or a steam canner.
Atmospheric Steam Canner
Examples of items commonly water-bath or steam canned include:
- Jams and Jellies
- Tomatoes (with added lemon juice)
Some borderline acidic food are further acidified with ingredients like lemon juice, lime juice, or vinegar.
When a recipe calls for vinegar, it is important to always use 5% vinegar. Food scientists use this level as a standard. Using a weaker strength vinegar can lead to an unsafe product. (Homemade vinegar and some rice vinegars are often not 5%.)
For recipes calling for lemon or lime juice, always use bottled juice. Bottled juices have a standardized level of acidity. Fresh lemons and limes can vary in strength.
Do not substitute or reduce the amounts of acid ingredients called for in recipes.
Tip: recipes with a lot of vinegar such as pickles and mustard will mellow and improve in flavor after a couple weeks of rest.
Although they have been around for decades, using atmospheric steam canners to process high-acid foods (pH<4.6) has been tested and approved by the UC Cooperative Extension for home canning.
We like steam canners because they are lighter to move and take less energy to heat up than traditional boiling water-bath canners.
While steam canners are now considered safe, their use varies slightly from water-bath canning.
This fact sheet from UC covers how to safely use steam canners and is worth reading if you are new to this type of equipment.
The processing time for steam canning is the same as water bath canners.
Note: It is important that while your food is processing that the lid does not move around or "burp." This can allow cold air to enter as the lid rises, cooling the contents for the canner.