What causes seal failure or lids to seal then unseal?
The use of up-to-date home canning utensils and supplies, following the manufacturer’s recommended lid application techniques and heat processing steps are all essential for sealing success with home canning two-piece metal lids. The most common causes of seal failure are: Insufficient heat processing of filled jars. When filled jars are not heat processed and/or when the heat processing method or time are inadequate for the type of food and jar size, excess air is not vented from the jars and microorganisms that cause food spoilage are not inactivated. Initially, some lids may appear to seal. i.e. curve downward. However, these same lids may unseal during shelf storage. The seal failure at that time is caused by one of two reasons: 1) Very low vacuum was created initially. Low vacuums do not hold over time. 2) Due to inadequate heat processing, food begins to spoil inside the jar. This spoilage produces gases that force the lid to release. All filled jars, regardless of their content,