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If you’re anything like me, the concept of degassing coffee was probably a bit confusing when you first heard it.
Freshly roasted coffee is supposed to be best, and you’re supposed to keep it in airtight containers to keep the coffee fresh. So what’s all this about letting it rest and degas?
This article will explain everything you need to know about it, particularly if you roast your own beans at home. Learning more about the degassing process will help you get your best cup no matter how you brew.
What is coffee degassing?
The standard wisdom is that freshly roasted coffee beans are best. After all, many of the complex aroma compounds that make a great cup of coffee can oxidize and degrade over time.
However, it is possible for coffee to be TOO fresh. Coffee after roasting is full of carbon dioxide that has formed during the roasting process.
When you try to brew this coffee, the hot water causes the carbon dioxide to rush out of the beans quite quickly, really interfering with the extraction process that is supposed to create great coffee. The result is a flat-tasting cup.
This effect is even more pronounced when making espresso, thanks to the short extraction time.
Degassing is the process of letting your roasted coffee beans rest, so the gas that has built up during the roasting process gets released into the air rather than your cup.
It’s a balancing act. You don’t want to wait too long, because the presence of some carbon dioxide in your roasted beans is a big indicator of freshness.
Thankfully, degassing is a simple process that anyone can do easily. If your coffee beans were packaged in a bag with a one-way valve, you just need to leave them on the counter in the bag. If you roasted your own and need to find a container, look for a coffee degassing container that will block out light and oxygen while still allowing the gas to escape. More on that at the bottom of this article.
Why does coffee need to degas?
Coffee needs to degas for a simple reason: The carbon dioxide in a batch of freshly roasted coffee beans will release when it meets hot water for the first time. You may have seen coffee bubble up during “blooming.” This is the gas escaping your ground coffee.
While this gas does help create a nice crema on top of your espresso, too much of it will prevent the water from evenly extracting your beans. The result could be a flat-tasting, acidic cup. You also won’t get all the delicious flavor notes that developed during roasting.
It’s particularly noticeable with espresso, because you’re interfering with an extraction that is already very short in duration. If you love a good espresso, be prepared to wait in order to have the most flavorful extraction possible. It’s less noticeable with brewing methods like French press because the coffee is in contact with the hot water for longer.
The coffee’s roast degree also has an effect. If you prefer a lighter roast, it will take longer to degas than a dark roast. This is because the bean is more intact, so there are fewer cracks from which the carbon dioxide can escape. Ground coffee also degasses more quickly. (However, it also goes stale more quickly—you may miss out on the full flavor of the bean if you store ground coffee for any length of time.)
How long does coffee need to degas?
Degassing time depends on the roast and how you intend to brew. Much of the gas will be lost in the first few hours after roasting. Within 72 hours, you can get the full flavor of a dark roast in a French press. Lighter roasts will take longer. You may be looking at up to a week for lighter roasts or for brewing methods with quicker extractions. Espresso takes the longest. With espresso, you’ll get the best extraction anywhere from seven to 12 days after roasting.
If you buy a new roast of coffee fresh, you can learn the ideal degassing time simply by brewing a cup every day and taking note of how many days off roast you are when you get your best cup. Then you’ll have that information whenever you buy that roast again. Every coffee is different, though, so you’ll need to do it with each new coffee you buy.
Can you grind coffee right after roasting?
You may be tempted to grind your roasted beans to speed up the process. While this will get rid of carbon dioxide quickly, you’ll risk having your coffee go stale prematurely. Coffee grounds have a much shorter shelf life than whole beans. For the best cup possible, let your coffee degas whole and then grind the beans right before you intend to brew.
For reference, remember that coffee degassing takes longer with lightly roasted beans. The shorter the extraction time of your brew method, the longer your beans need to degas. In general, this is how long to degas based on your brewing method:
Degassing time for different brewing methods
|Pour over/drip||2-7 days|
|French press||2 days|
How do you know if your beans still need time?
The biggest test comes from brewing a cup of fresh coffee. But if you don’t want to waste coffee that might not be ready, there are a few ways to test whether your coffee is finished degassing.
The simplest is to pop some beans into a resealable plastic bag. Squeeze out all the air and leave the bag overnight. If the bag puffs up, it’s still degassing—no matter how many days off roast you are.
With darker roasts, you can tell by looking at your beans. They should still look a bit oily and leave residue on your hands when you handle them. If you notice that neither of these is true, brew those beans quickly before they become too stale.
Lighter roasts are harder to assess visually than darker roasts, but the bag test should help with them. Just remember that they will take significantly longer to degas than your dark roasts. You need plenty of patience to get the best cup possible.
Storage for degassing
When you want to degas, storage is important. Most store-bought coffee is shipped in bags with one-way degassing valves that will let out carbon dioxide without letting in oxygen, so it should be degassed by the time you get it.
Buying fresh from the local roaster is different. Storage becomes an important factor. Anything fully airtight will trap the carbon dioxide, and the released gas may cause your container to explode if it’s left on its own for too long.
If you can find a container with a degassing valve, this will let you seal up your coffee immediately after roasting. If you can’t, you can use a typical airtight container but be sure not to seal it fully for at least 24 hours. Then return a couple of times over the next day to open the container and let out any carbon dioxide. Keep it brief, because you will also be letting in oxygen and oxygen is—along with light and moisture—one of coffee’s enemies.