Should you let espresso beans degas?

Coffee freshness has been one of the hot topics discussed by the SCA in recent years. Swiss chemist Samo Smrke presented at the SCA annual conference two years ago on the relationship between CO2 content and coffee freshness, as well as the factors affecting CO2 emission.

The study shows that roast level and roast time have a strong impact on both the volume of emitted gases and the activity of the emissions.

The darker the roast, or the shorter the time taken to reach the target roast level, the greater and faster the gas emission within the same period.

That’s why we often find that lighter roasts, and coffees roasted with flatter roast profiles, tend to have a longer shelf life.

What impact does using overly fresh beans have on extraction?

In espresso experiments, we can easily observe that freshly roasted beans often produce very thick crema. However, the brew stream tends to be thicker and more prone to large bubbles. Although there’s plenty of crema, the bubble sensation is heavy, and the taste is somewhat inferior. In terms of flavor, due to the obstruction caused by CO2, the extraction yield may be lower than expected. Some lighter-roasted coffees are more likely to produce astringency.

Moreover, for certain brewing methods that judge the coffee-to-water ratio based on espresso volume, overly fresh beans are more likely to cause misleading results. Additionally, espressos with too much gas can lead to frequent burping or flatulence, which can be quite damaging to a barista’s image.

Therefore, espresso beans used for making espresso also need to degas.

On the other hand, degassing isn’t something that should go on indefinitely. Stale beans lose all their CO2, and their volatile aromatic compounds have dissipated as well. When brewing espresso, it becomes difficult to produce crema. The flavor becomes dull, and may even develop a slightly sour or rancid smell.

Darker roasts fare even worse over time. Most coffee enthusiasts have probably smelled the oily beans sitting on supermarket shelves, or the rancid oiliness from dark roasts stored for too long — definitely not a pleasant aroma. If someone tries to put such beans into your grinder, please stop them. Oxidized coffee oils on the burrs can affect the flavor of your subsequent brews for several rounds.

One-way valves, while preventing the packaging from bursting due to gas buildup and blocking external odors from affecting the coffee’s flavor, aren’t necessarily the only option for preserving roasted beans. For instance, Illy fills its tins with nitrogen to extend freshness. Sometimes we can also cover the one-way valve with tape to regulate the rate of CO2 emission, allowing the coffee to mature slowly without losing its freshness.

Why degas? And for how long?

You’ve probably heard about degassing. Freshly roasted coffee shouldn’t be brewed right away but should be stored in a cool, dry place for a few days before it tastes good. There are many reasons for degassing, with countless theories and hypotheses, but most baristas agree that freshly roasted coffee beans undergo intense chemical changes, leading to unpredictability and variables during brewing. Thus, degassing is an inevitable process.

The main purpose of degassing is to “release gas.” During roasting, coffee loses a significant amount of moisture. At the same time, the high temperature causes the cell walls to expand, resulting in far more pores in roasted beans than in green beans. These pores store a large amount of gas.

The key to degassing is bringing the internal fiber pressure of the bean back in line with ambient pressure. Therefore, the degassing time is related to the roast level and also to the roasting technique (the ROR, or rate of rise curve). These variables affect the internal fibers differently. Common degassing times generally shorten as the roast level deepens, which correlates with the intensity of gas release.

Of course, the brewing method is also a factor we must consider. Generally, baristas use pressurized vs. non-pressurized extraction as a reference point because, in a pressurized espresso environment, CO2 dissolves more easily into the coffee liquid. The crema we taste is a golden foam formed by aromatic compounds, lipophilic substances, and CO2.

In normal espresso extraction, there’s no operation similar to the blooming step in pour-over brewing. The amount of CO2 has a particularly noticeable impact on pressurized extraction. Excess CO2 not only hinders the contact between hot water and coffee grounds, thereby reducing extraction yield, but also increases the chance of channeling (piercing effect). Therefore, espresso beans usually require a longer degassing time than coffee beans used for pour-over. For example, my personal medium-dark roast espresso beans are degassed for about 10 days, while pour-over beans are ready to use after just 4–7 days.

How long should your espresso beans degas for?

It’s best to ask the roaster who sold you the beans — they’ll give the most accurate answer.

Degas talk may sound like a devilish detail, but it’s also a subject worth exploring. Degas must be discussed on a case-by-case basis to be meaningful, because there are so many variables in coffee. Judging based on just a few conditions would be seeing the trees but missing the forest. Finally, our advice is this: once your brewing skills become more stable, or when using simpler brewing methods like cupping or a clever dripper — which reduce the impact of brewing and stabilize variables — you can more accurately understand the cause-and-effect relationship between degassing and coffee flavor.