Shelf-stable oat milk means that you can leave it in the kitchen cabinet or pantry. Provided it's properly stored, you can keep it outside, which can last for months. You'll know if you have shelf-stable oat milk if it doesn't sit in the supermarket fridge. It's shelf-stable as it's packaged in aseptic formats, producing a completely sterile environment. Because of this, it has a longer shelf life and doesn't require refrigeration until you open it.