The importance of following tested recipes and safe processing methods for canning food safely depends on several factors. They include:
- pH or acid content of the food. The 12-24 hours post-processing must show pH equilibrates and must not change after that time.
- Heat penetration rate at the cold spot inside the jar. This is depends on how the food heats, whether by convection or conduction, the size of jar, food consistency, and the amount of headspace.
- Initial pack temperature is the temperature of the food going into the jars. This temperature can change 30-40°F depending on number of jars and fill efficiency.
- Soluble solids (°Brix) content includes the amount of sugar in the food solution. It is measured with a refractometer. The higher the °Brix, the less water available for bacteria to grow.
- Water activity measures the amount of water available for bacterial growth.
Source: Newell Brands, Inc.