Here's why:

* Fruit Respiration: Fruits continue to respire even after being harvested. Respiration is a process where fruits use sugars for energy and release carbon dioxide as a byproduct.

* Anaerobic Respiration: In the absence of oxygen (which is limited inside a sealed can), fruit cells can switch to anaerobic respiration. This process produces even more carbon dioxide.

* Other Gases: While carbon dioxide is the primary gas, other gases like ethylene (a ripening hormone) can also be produced by the fruit.

It's important to note that:

* The amount of gas produced varies depending on the type of fruit, its ripeness, and the storage conditions.

* Canned fruits are typically processed to remove oxygen and reduce the risk of gas buildup.

* If you notice significant gas buildup in a canned fruit, it might be an indication of spoilage or improper storage.