Why Does Coffee Get Stale?
The Food Scientist answers vexing food questions
Whether you call it a cup of joe, java, battery acid, Juan Valdez or mud, the one thing you never want to call your coffee is stale.
What is stale coffee?
Just as iron is oxidized to form rust, stale coffee is what you get when roasted beans (or grounds) have been oxidized from exposure to oxygen; the more intense the exposure, the more quickly oxidized and stale your coffee will become. Other factors such as heat and moisture can also make oxidation occur. In your mug: rancid, bitter coffee for which no brewing technique on earth can undo the damage.
How do you prevent coffee from going stale?
When defending your daily roast from stale defeat, remember these simple tips. First, never buy pre-ground coffee beans. When beans are pulverized into a fine or coarse grind, the oxidation process is accelerated. This means that grinds exposed to air will become stale faster than if the beans were left whole upon purchase. You’d never slice a fresh apple and leave it in your kitchen for days before eating it, would you? The same courtesy should be applied to your coffee stash. Grind your beans as close to brewing as possible, and only grind as much as you need to avoid any waste.
The second tip is about storage. Be sure you’re using an airtight container, like a jar with a rubber-sealed lid when storing your fresh beans. This definitely takes care of oxygen and moisture exposure, but what about heat and light? While the method of choice for some is to toss those beans in the freezer, there are plenty of arguments suggesting that freezing may damage the delicate balance of oils and flavors and detract from the flavor of your coffee. As a safe alternative, store your airtight jar in a cool, dark cupboard as you would any good bottle of wine.