Paper bags are probably to blame. They provide little protection against air and moisture. Below is a detailed explanation of why this happens:

Granola is a common snack. It comes in a variety of packaging options – cardboard boxes, paper bags, plastic stand up bags, and others. Each of these packaging methods has advantages and disadvantages.

Cardboard boxes look good, but they provide little protection from moisture once the box has been opened. Paper bags are more environment friendly than plastic bags, but they do not do a good job of protecting granola inside. Stand up bags, which are made from plastic, provide a middle way out – they are more environment friendly to produce than cardboard boxes and they provide a stronger barrier than paper bags.

Stand up bags can be reinforced with side gussets. These side gussets give the food pouches a box-like appearance and increase the available area for advertising. If the trail mix packaged in these bags is for multiple uses, a few other accessories can be added to these bags to make them more suitable for granola packaging.

The zip lock of these bags is designed in such a way that it provides an effective barrier against moisture and other environment factors that can make your granola stale. Even with zip locks, these bags prove to be less expensive than glass jars – which are an alternate method of packaging granola at home.