When we buy coffee beans, we can often see a white valve in the coffee bean packaging bag, and a silver film in the coffee bean bag. What is the role of these two things?First of all, the white valve is a one-way exhaust valve, and roasting coffee beans will naturally emit carbon dioxide. If left in the package, the quality of the coffee beans will suffer. Through this one-way degassing valve, the carbon dioxide produced can exit the packaging, so that the quality of the packaged coffee beans is not compromised.Secondly, the silver film is made of the same material as tin foil, which we call professionally:aluminum foil. Aluminum foil can act as a moisture-proof, light-proof and barrier, preventing coffee beans from coming into contact with light and air, which can cause coffee beans to emit and oxidize their aroma.All in all, aluminum foil plus one-way exhaust valve can better prevent air from entering, keeping coffee beans fresh and pristine.Therefore, aluminum foil bags and one-way degassing valves must be used in coffee bean bags.