"The patented Freshness Valve is the key to eliminating trapped CO gas. The valve is constructed with a unique filter that allows carbon dioxide gas to pass through without allowing oxygen or other gases back in. This one-way valve removes the trapped gas that breaks down and destroys coffee flavor over time. All coffee is roasted, both whole bean and ground. This roasting process heats the coffee bean and caramelizes the sugars in coffee. It is this roasting process that creates the flavor degrading gas. Coffee is perishable much like fruit, milk or bread -- keeping coffee fresh is very important. Without a freshness valve coffee can not be kept fresh."
I bought these just to store my ground coffee in, but was wonderfully surprised to find the coffee flavor improved. After grinding our coffee, it use to start to get a bitter taste. No longer. Well worth the purchase price and a must for any coffee drinker.