This hole is actually a valve device, called one way exhaust valve.
After the coffee beans are taken out of the oven and cooled, they will be put into a sealed bag. If there is no coffee exhaust valve, a large amount of carbon dioxide will fill the entire bean bag. When the bean bag can no longer support the gas continuously emitted by the beans, it is easy to be bulged.
When there is a coffee exhaust valve, the bag is filled with gas, and when the beans emit new gas, the internal pressure will be higher than the external pressure. Thus, the exhaust valve sheet is pushed open to discharge the excess gas outward. When the excess gas is discharged, the pressure returns to normal, and the coffee exhaust valve returns to the closed state. Therefore, the one-way exhaust valve has only one simple function: to prevent gas from bursting the packaging bag.
