Why are fruit cans exhausted before they are sealed?

In the context of canning, fruit cans are exhausted before they are sealed primarily to remove trapped air from the container.12

This process is essential for several reasons:

• Vacuum Creation: By heating the contents in an exhaust box or using mechanical vacuum-sealing machines, the food expands and drives out air. Once the can is sealed, heat-sterilized, and cooled, the contraction of the contents creates a partial vacuum within the container.1
• Quality Control: The presence of this vacuum causes the ends of the processed cans to become slightly concave, which serves as a standard indicator of a properly sealed product. Conversely, bulging ends may indicate a loss of this vacuum, signaling potential deterioration or spoilage.3
• Microbial Safety: Removing air helps establish anaerobic conditions, which prevent the growth of oxygen-requiring microorganisms.2

Exhausting ensures that the final product is shelf-stable and maintains its integrity throughout storage.12