Why Espresso Beans Need a Longer Rest Than Pour-Over Coffee (Coffee Degassing Explained)

 It’s widely known that freshly roasted coffee beans are not ideal for brewing right away. During roasting, coffee beans accumulate a large amount of carbon dioxide inside their structure. When too much CO₂ is present, it interferes with hot water’s ability to extract aromas and flavor compounds, resulting in a cup that simply doesn’t taste as good.

Fortunately, carbon dioxide naturally escapes from the beans over time. By allowing the beans to rest, we reduce the amount of CO₂ trapped inside. Once the gas level drops to the point where it no longer significantly affects extraction, it becomes much easier to brew a great-tasting cup of coffee. This resting window is what coffee lovers commonly refer to as the “degassing” or “resting” period.

If you regularly buy whole beans and brew at home, you’re probably familiar with this concept. Beans used for pour-over brewing typically need about 3 to 7 days of rest, depending on the roast level. However, if you’re buying beans intended for espresso, you’ll notice that the recommended resting period is usually several days longer.

Many people find this confusing. After all, coffee beans are coffee beans—so why do espresso beans need more time to rest?

The answer mainly comes down to two factors, the first being roast level.

I’ve mentioned before that coffee beans roasted for espresso are generally darker than those intended for pour-over. The reason is simple: a darker roast increases sweetness and flavor intensity while reducing acidity.

Espresso isn’t just consumed as straight shots—it’s also the base for milk-based drinks like lattes, cappuccinos, and flat whites. If the roast is too light, the coffee flavor won’t be strong enough and can easily be overwhelmed by milk.

On top of that, lighter roasts tend to retain more acidity, which doesn’t always pair well with milk. The result can be a milk drink that tastes sharp or unbalanced. Because of this, many roasters use different roast profiles for the same coffee depending on the intended brewing method.

If a coffee is meant for pour-over, cold brew, or other single-origin brewing styles, it’s usually roasted lighter to preserve floral aromas and fruity notes, allowing you to experience more nuanced flavors. If that same coffee is intended for espresso, the roast will typically be slightly darker to ensure enough intensity to stand up to milk and to create a more harmonious flavor profile.

For example, Ethiopian Gesha is a coffee I often mention. If you’ve ever purchased it from my Taobao or Tmall store, you may have noticed that it’s offered in two roast levels: a light-medium roast for pour-over and other filter methods, and a medium roast designed specifically for espresso.

The darker the roast, the more carbon dioxide the beans tend to contain. Naturally, this means espresso beans—being more deeply roasted—require a longer resting period to release excess CO₂.

At this point, some people might ask: If I use the same coffee and the same roast level for both espresso and pour-over, shouldn’t the resting time be the same?

My recommendation is still to rest espresso beans longer.

This is because carbon dioxide has a much greater impact on espresso extraction than on pour-over. The key reason lies in the brewing method itself.

Pour-over, cold brew, French press, and siphon brewing all take place under normal atmospheric pressure. In these methods, extraction is relatively controllable. You can adjust variables like agitation, brew time, water temperature, and grind size to manage extraction efficiency. Under these conditions, the influence of CO₂ is noticeable but generally manageable.

Espresso, on the other hand, is brewed under pressure. With pressure assisting extraction, we can produce a highly concentrated coffee in a very short amount of time. To achieve this, espresso requires an extremely fine grind and relatively high water temperature, pushing extraction into a very intense and unforgiving zone.

As a result, extraction control is lower, and the negative effects of excess carbon dioxide are amplified.

Because espresso shots are brewed quickly and yield a small volume of liquid, there’s very little opportunity for gas to escape during brewing. When too much CO₂ is present, it becomes difficult to achieve a fully extracted, well-balanced shot without extensive dialing-in. That process consumes both time and beans, making it costly and inefficient.

For this reason, when a coffee is intended for espresso, it’s best to let it rest a few extra days. Once the carbon dioxide level drops to the point where it no longer interferes with extraction, you’ll not only save time and beans during dialing-in, but you’ll also end up with a far more delicious espresso.