Why a Coffee Bag Has a Valve and What It Can Tell You

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 plays an important role in keeping your coffee fresh and tasting great.

Once you know what the valve is for, you can even use it to determine how fresh the coffee beans are. Here we'll explain why.

Why Coffee Bags Have a Valve

During roasting, coffee beans develop the enticing aromas we associate with a fresh cup of coffee. That 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.

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 continue to give off carbon dioxide for a few weeks after roasting (especially dark roast beans, which are roasted longer than other varieties).

Without an exit point, those gasses 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 makes your coffee go stale or bad more quickly.

How to Use the Valve to Determine Coffee Freshness

Coffee is usually at its prime a few days after roasting. When coffee beans are bagged shortly after roasting, they'll continue releasing carbon dioxide inside their packaging.

The valve helps you determine which bag of coffee to buy. Over time, the aromas 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, 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.

Coffee in Cans vs. in Bags

Coffee in cans is different. As you've noticed, cans 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.