Michigan State University Extension
Preserving Food Safely - 01600953
Do not taste food from a jar with an unsealed lid or food which shows signs of spoilage. You can more easily detect some types of spoilage in jars stored without screw bands. Growth of spoilage bacteria and yeast produces gas which pressurizes the food, swells lids, and breaks jar seals. As each stored jar is selected for use, examine its lid for tightness and vacuum. Lids with concave centers have good seals.
Next, while holding the jar upright at eye level, rotate the jar and examine its outside surface for streaks of dried food originating at the top of the jar. Look at the contents for rising air bubbles and unnatural color.
While opening the jar, smell for unnatural odors and look for spurting liquid and cotton like mold growth (white blue, black, or green) on the top food surface and underside of lid.
Carefully discard any jar of spoiled food to prevent possible illness to you, your family, and pets. Before discarding, detoxify spoiled low-acid food. Remove the jar lid; then place the jar, its contents, and the loose lid in hot water and add enough water to cover the jar. Boil all items in the water for 30 minutes. Cool and discard jar contents in garbage or bury in soil. This will prevent accidental poisoning.