Why Do Coffee Bags Have Vents? (Mystery Solved)

Last Updated on May 18, 2022 by John Moretti

Regardless of how or where you buy coffee, you may have noticed that almost all bags of coffee, whole bean or otherwise, are fitted with a valve in the bag. This is true for bags of coffee bought from supermarkets and from roasteries alike, but why do coffee bags have these vents?

Coffee bags have vents to allow gases from the coffee to vent without allowing air from outside the bag in. Gas from the coffee builds up within the bag. Without a valve, the gases build up and cause the bag to burst. The vent does not allow air into the bag, and the coffee goes stale. 

The vent in a bag of coffee is far more important than most people realize, and it is not for smelling the coffee before you buy it, as some may believe. The importance of this vent cannot be understated as it helps keep coffee ready to brew during shipping and storage. Let’s learn more about this vent and answer as many questions surrounding it as we can.

What Is The Coffee Bag Vent For?

Coffee Bag Vent

Anyone who has examined a bag of coffee will have seen the small round vent that almost every bag of coffee is fitted with. This small vent is critical for shipping and storing coffee, especially freshly roasted coffee, for one important reason: degassing.

The truth is, the vent in a coffee bag is a one-way valve rather than a regular vent. This valve is designed to let gases from within the bag vent out to the atmosphere without allowing any gasses from outside the bag to enter. 

When coffee beans are roasted to prepare them for brewing, they produce a lot of carbon dioxide gases. Most of this gas escapes the coffee beans during the roasting process, but a significant amount remains left behind, locked within the beans. This gas, however, slowly escapes over time in a process called degassing. 

These vents in bags of coffee allow the gasses that leach out of the roasted coffee to exit the bag safely. If these gasses are not provided with a means to exit the bag, they will build up inside the bag, eventually causing the bag to rupture. 

If the bag does not rupture, then the gas levels within the bag will reach critical levels and not permit any more gas to leave the beans. If degassing is halted, the beans will not be ready for brewing by the time the packaging is opened. 

This one-way valve allows the coffee beans within the bag to effectively degas without the risk of the escaping gases rupturing the package due to the accumulation of internal pressures and without allowing oxygen from the air outside the bag to enter in and cause the coffee to go stale. 

In short, the valve fitted into a bag of coffee allows the coffee to continue with the natural processes that make it good for brewing even during shipping, ensuring that the coffee reaches you safely and is ready to brew. 

Why Is Degassing So Important?

We have established that the valves in bags of coffee allow the coffee to degas while shipping and during storage, but why is this process so important?

Degassing is an important process that allows the stored carbon dioxide gases within the coffee beans to escape. This is critical because coffee that has not been fully degassed will not brew very well.

When the coffee beans are ground and have hot water introduced to them, any remaining gas within the coffee will rapidly escape. This rush of gas leaving the coffee hinders the brewing process by forming a bubble of gas around the grains of coffee, preventing the water from reaching all of the coffee.

This will lead to an under-extracted brew and will produce a sour, empty-tasting, and disappointing cup of coffee. 

Degassing is vital for all coffee, which is why the valve in coffee bags is so important. The valve is more important for re-ground coffee than for whole beans, but every bag should be shipped with a functioning valve to allow the coffee to degas properly without allowing the coffee to go stale. 

Do All Coffee Bags Have Vents?

Coffee Bag

If degassing is so important for coffee beans, and it is well known that the valve fitted into coffee bags allows this process to occur during shipping, does every bag of coffee always come with this type of valve installed?

The truth is, not every bag of coffee that you buy will have a one-way gas-exchange valve. However, most bags will. If you buy coffee from a large store, a supermarket, a very large coffee chain, or even a coffee shop, you are guaranteed that the bags of coffee that you buy will have a gas-exchange valve. 

The only instance when these valves are not always included in coffee bags is when the coffee is sold and shipped by a small roastery. Most roasteries will use this type of valve in their packaging, but the very small or very niche roasters may not imply for lack of infrastructure or budget. 

Some coffee bean suppliers sell coffee beans by weight in-store. This means that a person can buy a number of coffee beans by weight from the selection available. This coffee is usually weighed out in paper bags and not sealed at all. 

There is nothing wrong with coffee that is sold or shipped without a gas-exchange valve, and it simply means that the coffee must be allowed to degas after opening the package if it has not already degassed before purchase. 

What If The Coffee Bag Valve Fails?

Coffee Bag Valve

An important question about this type of valve in coffee bags is what happens if the valve fails? Is the coffee still good to use, and what should you do if you buy a bag of coffee with a failed gas-exchange valve? 

If the valve in a bag of coffee fails, the bag is likely to rupture from the buildup of gases within the bag released by the coffee, which means that you are unlikely to ever buy a bag of beans with a faulty gas-exchange valve. 

However, if the coffee arrives at your house soon after the valve fails before the bag ruptures, the coffee is still perfectly good to use. 

A failed valve will result in a bag that is inflated and stiff from the release of gas within the bag. However, if you have a bag of coffee like this, do not be concerned. The coffee is good to use; all you have to do is open the bag and allow the coffee to degas properly for a day or two before brewing the coffee. 


This coffee bag valve is meant to ensure that your coffee arrives at your home sealed within the packaging, to ensure that the coffee itself is allowed to degas properly before you get it, which means that it will be ready to brew when it arrives and the valve prevents the coffee from going stale too quickly by not allowing any fresh air into the bag. 

All of this means that this simple invention keeps your coffee good and fresh while allowing it to be brew-ready when you open the bag. The next time you acquire a bag of coffee, know that the little valve in the bag has kept your coffee in perfect condition all the way to your kitchen.