The Co2 part is correct, but I don't know about the need to pressurize them. My brother (who has a coffee roasting company) says the biggest enemy to coffee flavor is oxygen. He uses special coffee bags that have a one-way valve in them. Coffee, right after being roasted, continuously gives off Co2 for a while and the one-way values allows the oxygen in the bag to be displaced by the Co2, which leads to a very long storage life for the coffee as long as the bag is not opened.