We recently reviewed a scientific study done at the University of Minnesota on coffee staling and found some interesting results. The biggest factor, by far, in the perception of stale coffee is oxidization of coffee lipids. Exposure to oxygen caused tasters to notice staling effects within 2-4 weeks of roasting. When oxygen was not present (FYI, we seal our coffee in nitro-flushed bags), tasters could not detect stale coffee flavors for 30 or more weeks. The study also looked at temperature and noted that coffee stored at 90 degrees Fahrenheit, when sealed and free of oxygen, did not notice stale.
Once your sealed bag is opened, you will need to consume that coffee within a few weeks to preserve its flavors. If you open a bag and know that you are not going to brew the coffee, the study suggests that freezing will extend shelf life by a few more weeks. Unfortunately, the effect is magnitudes smaller than oxygen free storage, so you should expect your unsealed freezer coffee to lose flavor quality within a month.
Our main conclusion from reviewing the study is that you don’t need to worry much quality loss in your coffee, assuming the bag stays sealed, regardless of temperature. As soon as you open your bag, plan to brew it within a few weeks, or freeze a portion in a sealed ziploc bag.