There’s a lot to think about when perusing the coffee aisle in your supermarket. Dark or light roast? Whole beans or ground coffee? (Hint: Always beans.)
Ingredients
What Is That Valve on My Coffee Bean Bag?
That tiny piece of plastic has a big job.
By Published May 17, 2024.
Another thing to consider: the bag.
When shopping for coffee, you may have noticed a round button-shaped device located closer to the top of the bag; look closer, a small hole in the middle of the button lets out air.
That “button” is a one-way valve—air can flow out of the bag, but outside air can’t make its way in.
Sign up for the Well-Equipped Cook newsletter
Shop smarter with our ATK Reviews team's expert guides and recommendations.
America's Test Kitchen will not sell, rent, or disclose your email address to third parties unless otherwise notified. Your email address is required to identify you for free access to content on the site. You will also receive free newsletters and notification of America's Test Kitchen specials.
What Is the Valve on Coffee Bean Bags for?
The one-way valve was designed in such a way as to “degas the bag,” said Logan Allender, the chief operating officer of Atlas Coffee Club, a coffee subscription company based in Austin, Texas. “As part of roasting, more specifically sugar browning, you create carbon dioxide,” he explained. Without a proper way to let out the air, bags would balloon up as the gas continues to release for a few days after roasting.
Does the Valve Keep Coffee Fresh After It’s Opened?
It depends. If you remember to seal the bag after taking out the beans you need, the one-way valve will keep the outside oxygen from creeping in. “Since CO2 the coffee generates is heavier than air, it will eventually push out any oxygen [that remains],” Allender said, referring to the new oxygen that sneaks into the bag after opening.
How to Tell If Your Coffee Is Fresh
You don’t have to be a barista to tell if your coffee has gone stale.How to Keep Whole Beans Fresh
The general rule of thumb, according to Allender, is to store whole beans in a cool, dry place. Some people decant their coffee into a storage container. Some people leave the whole beans in the bag as they go through them. Either is fine. “A resealable bag works great,” Allender said. Allender cautioned that the one caveat with storing coffee in a separate canister is that it requires regular maintenance to clean out any oils, especially for dark roast fans.
The easiest solution? Simply store the beans in the bag they came in. Just make sure to fold the bag over tightly so as little air as possible can get in. Roasted coffee will naturally keep generating carbon dioxide, which balloons the bag over time. Fold again to push out excess air after you reopen the bag to take out the beans.
Is It OK to Grind Coffee Beans Ahead of Time?
The general rule of thumb is to grind your beans right before brewing. Colby Cox, a coffee roaster for Atlas Coffee Club, likes to tell consumers to treat coffee the way they would treat any spices, which are “best when ground fresh.”
He explained that “exposing more surface area exposes more volatile oils that go bad with oxidation over time.” Oxidized coffee will then lose its aroma and impart an overly bitter and rancid taste in your cup.