If you've ever perused bags of coffee at the grocery store or while waiting in line at the coffee shop, you might have noticed that most of them have a small hole or a plastic valve near the top of the bag. What you might not realize is the valve actually plays an important role in keeping your coffee fresh and tasting great as it sits on the shelf. Once you know what it's for, you can even use it to help determine how fresh the coffee is that you picked up.
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When coffee is first harvested, it looks nothing like the hard, brown, roasted beans we're used to seeing. Coffee beans actually grow in pods, and the pods can be light green, yellow, or even bright red—an entire container of them looks a little like a bowl of cherry tomatoes. The beans we brew into coffee are on the inside, and they start out mostly colorless. The roasting process is what turns them dark brown, and makes them hard enough to grind.
However, the roasting process changes more than just the coffee bean's appearance. As beans roast, the enticing aromas we associate with a fresh cup of coffee start to develop, and the chemical reaction creates a lot of carbon dioxide. Some carbon dioxide is given off during the roasting process, but even more is released after the roasting stops and the coffee beans rest. For a few days after roasting, coffee beans undergo what's called the "degassing period," and that's where the valve and holes you see on your coffee bag come in.
During the degassing period, the coffee beans continue to release carbon dioxide, which is good—that release helps preserve your coffee's flavor and aroma. But the degassing doesn't happen all at once. While the most carbon dioxide is released in the first few hours and days after roasting, coffee beans can continue to give off carbon dioxide for a few weeks after roasting (especially dark roast beans, which are roasted longer than other varieties).
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But coffee is usually at its prime a few days after roasting, which means coffeemakers don't necessarily want to wait until the end of the degassing period to get their coffee on shelves. When coffee beans are bagged shortly after roasting, they'll continue releasing carbon dioxide inside their packaging. Without an exit point, those gasses can build up inside the bag and cause it to expand or even tear. A valve allows carbon dioxide to escape without letting oxygen or moisture in, both of which can make your coffee go stale or bad more quickly.
The valve can also help you determine which bag of coffee to buy. Over time, the aromas also escape through the valve along with carbon dioxide, so as your coffee ages, the smell becomes less potent. To check if a bag is fresh before you buy it, you can lightly squeeze the bag to release gas through the valve. A strong smell is a good indicator that the bag is fresh, and if you don't smell much after a light squeeze, it probably means that the coffee has been on the shelf longer, and might not have as strong of a flavor.
Cans are a different story altogether, as you've probably noticed they don't usually have a valve or hole. Usually, coffee is vacuum-packed into cans to protect it from moisture and oxygen, but unlike bagging, it usually isn't done until the degassing period is over. The difference is simple—while canned coffee has a much longer shelf-life than bagged coffee, it's less fresh when it's packaged. So if you want the strongest flavor, choose a bag, but if you want your coffee to last more than a week or two, grab a can.
Those tiny holes on your coffee bag might seem insignificant, but knowing what they're for can help you choose a better bag of coffee at the store. If your goal is to create the best brew ever, grabbing the right bag of coffee at the store can make your morning cup of Joe even better!