A hermetic seal has the quality of being airtight. In common usage, the term often implies being impervious to air or gas. When used technically, it is stated in conjunction with a specific test method and conditions of usage.
Because compounds that give coffee the flavor and aroma are volatile, roasted coffee beans are stored in airtight recipients. This prevents oxidation of some of the compounds, and volatilization of other compounds.
Storing coffee in containers with a hermetic seal is important across the coffee preparation process. Once coffee beans have been roasted they become subject to oxidation when in contact with the air. Therefore, it is important for the successful coffee manufacture and distribution process that all roasted coffee beans are stored in airtight containers.
Ground coffee is much more sensitive again to oxidation than roasted whole beans. It is highly recommended in the coffee industry that coffee beans are freshly ground before coffee is brewed. In nearly any coffee shop or establishment that serves brewed coffee beverages, it is standard for it to be freshly ground.
Pre ground coffee is still sold as standard in stores and supermarkets and is the normal way of consuming coffee for the majority of home coffee drinkers. It is also common practice to buy a bag of coffee beans at a speciality coffee shop and have them ground by the barista there, in order to avoid having to grind coffee beans at home.
In these situations where cups of coffee using pre ground beans are being brewed, it is paramount that pre ground coffee is stored in a container with a hermetic seal in order to try and preserve any remaining tastes or properties from the coffee bean.