The best way to keep your coffee tasting fresh is to buy whole beans and grind them when you're ready for a cup. But if you grind too much or buy pre-ground beans, all isn't lost. Lock that roasted flavor in by sealing and storing the coffee in a dark spot that's dry, cool and free of moisture. For longer-term storage of more than two weeks, consider picking up a vacuum sealer -- the expense might be worth it for a fresh cup of joe.
Buying Ground Coffee
Proper storage starts when you buy ground coffee at the supermarket or your local roaster -- choose the right bag, and find out when the beans were roasted.
Supermarket: Choose bags of ground coffee that have one-way release valves on the sides. These valves, a common packaging feature, keep oxygen out and promote proper aging. If the roast date isn't printed on the package, squeeze the bag gently and smell the air from the valve; it should have a fresh, intense aroma.
Local Roaster: Your local coffee maker might not use valve bags, so only buy coffee that was ground less than five days ago. Try to use it up within a week of purchase.
Week One Storage
Whether you buy your grounds from a supermarket or a roaster, once you open the package, oxygen starts to get in. This is fine if you'll use the grounds within the first week, especially if the package has a sealer, but you have to keep it away from moisture -- no fridge or freezer -- and in a dark, dry spot at room temperature. A shelf in a rarely used cupboard or the bottom shelf of the pantry are perfect.
If the package doesn't have a sealer, use a bag clamp that keeps the opening tightly closed; some coffee roasters and food supply stores have clamps specifically for coffee bags.
Week Two Storage
If you're storing your ground coffee for more than a week, transfer it to a container that has an airtight lid right after you buy it. This keeps more oxygen away from the coffee than a bag, meaning the freshness stays for another week. Use a ceramic or glass container, not metal or plastic, which can alter the flavor of the coffee -- and not for the better.
Storage -- Three Weeks or More
At the three-week mark, those fresh grounds won't be so fresh anymore, so if you think you'll be storing them for longer and still want fresh coffee, use a vacuum sealer and store the bags in the freezer. Vacuum sealers pull out all of the oxygen within the bag, preserving what's inside, and the cold darkness of the freezer prevents any contamination to the flavor. Although vacuum sealers also pull out some of the aroma and flavor, the coffee remains relatively fresh for up to six months.
Vacuum-seal bags with enough coffee to last you one week; this eliminates the need to repeatedly open and reseal a single large bag, which lets oxygen in. Don't return an opened bag to the freezer, but place the coffee in an airtight container and store it in a cool, dry place.
Once you remove the coffee from the freezer, let it come to room temperature before you brew it.