The Perfect Shape of Pour-Over Coffee Grounds! Can You Determine Brewing Skills from the Coffee Bed? How Long Should You Bloom Pour-Over Coffee?

Yesterday a friend shared an interesting observation with FrontStreet Coffee. He noticed that most people, when brewing, keep their eyes fixed on the changes in the dripper — even during the waiting intervals when no water is being poured — as if trying to glean some information from the coffee bed.

Surprisingly, quite a lot of information really can be gleaned from the dripper: the freshness and density of the beans, the grind size, the path and method of the pour, and much more. All of it can be observed during brewing. So today, FrontStreet Coffee wants to share what kinds of information we can read during the brewing process.

1. The Degree of Bulging During Coffee Bed Blooming

Blooming is a preparatory step in most brewing methods because it helps release large amounts of carbon dioxide from the grounds, letting the hot water poured afterward dissolve flavor compounds more effectively. During blooming, the released carbon dioxide forms bubbles when enveloped by water, and those bubbles push the coffee bed upward into a mound-like bulge.

The size of that bulge and the bed's water retention help us judge the freshness of the coffee, as both conditions depend mainly on carbon dioxide content. More carbon dioxide means a larger bulge, and vice versa. Also, because bubbles create barriers that slow water flow, more carbon dioxide means stronger water retention and a bed that stays moist longer; when carbon dioxide is insufficient, the bed dries out quickly. So we can judge freshness from the size of the bulge and how the bed holds water during blooming, because fresher beans retain more of the carbon dioxide stored during roasting, producing relatively larger bulges and better water retention.

Dark-roasted coffee often produces larger bulges than light-roasted coffee, because carbon dioxide content is also tied to roast degree: the deeper the roast, the more carbon dioxide accumulates in the beans. On top of that, the beans' expansion rate increases, which naturally produces a relatively larger bulge.

2. Raising the Coffee Bed Height

Raising the coffee bed is a pouring technique commonly used in brewing. It specifically means increasing the water flow rate so it exceeds the drainage rate, thereby raising the water level. The grounds in the dripper then rise uniformly with the water level and finally distribute evenly around the dripper. The advantage is that it helps reduce bypass water while letting hot water extract the grounds more evenly. (Detailed introductions can be found in previous articles.)

Not all coffee beds can be raised, though, as this relates to the quality of the grounds. When beans are lighter-roasted or higher in density, the grounds are too heavy to lift. So from whether the bed can be raised, we can judge the approximate density of the beans and then find a corresponding extraction approach.

For example, when the bed can't be raised, if we don't want to create too much bypass water that would make the coffee taste bland, it's best to appropriately reduce the flow, letting hot water pass through the coffee layer as much as possible so it does its extraction job.

3. Foam Color

During brewing, many bubbles float on the surface of the coffee liquid — the carbon dioxide bubbles FrontStreet Coffee mentioned earlier. Their color changes continuously throughout the brew, from dark brown initially, to golden, then to light yellow, and finally turning whitish. It's precisely from these foam colors that we can read information during brewing.

Because the foam color comes primarily from the coffee grounds, some extremely fine, lightweight particles mix into the foam and tint it. During brewing, the hot water we pour washes these fine particles out of the foam; without them, the foam color gradually fades. So when we see certain foam colors lighten or even turn whitish, it tells us our pouring has concentrated in those areas. In other words, from the foam color we can see the path of the pour.

4. Water Flow Rate

Next is the water flow rate, which is affected by many factors — density, grind size, dripper, and more — but typically the speed of flow depends mainly on grind size and bean density. A faster flow usually means the grounds are coarser, giving the hot water more space to move and draining faster. A slower flow means the grind is finer or the grounds are denser; once they settle, the gaps between them shrink, leaving less room for water and reducing the speed.

Another cause of slow flow is excessive fine particles clogging the filter holes. Because so many factors affect flow speed, though, this situation usually needs to be combined with the fifth point to reach a conclusion. Everyone should know that we can't directly judge whether a cup will taste good from flow speed alone, because besides extraction time, many other factors affect extraction. Ultimately, we still need to combine this with taste to decide whether parameters need adjusting.

5. The Shape of the Coffee Ground Crater

Finally, the shape of the coffee-ground crater. Many beginners chase a deep, uniform crater after brewing, partly because such craters look symmetrical and pleasing, and partly because it's often rumored online that a deep crater means the coffee tasted good.

In reality, the formation of the crater has no direct relationship with whether the coffee tastes good. It only reflects our pouring method during brewing. The technique of raising the coffee bed, for example, can contribute to deep craters. Beyond that, there are many different types of craters, and as FrontStreet Coffee mentioned, they reflect different pouring methods. A flat-bottomed crater, for instance, means we didn't use too much flow during brewing; a layered crater means our flow was too large or concentrated on certain edges. Because there are so many types of craters, FrontStreet Coffee won't elaborate here; interested friends can turn to the article "Complete Guide to Pour-Over Coffee Ground Craters."

So that concludes this article. If there are other details worth noting during brewing, feel free to leave a comment and let's discuss together.

FrontStreet Coffee Recommendation

The bulge you see during blooming depends on how much carbon dioxide the beans are still holding, so it's a direct read on freshness — and on roast level. FrontStreet Coffee's Ethiopia Huakui is a light-roasted natural whose tropical-fruit aromatics of strawberry, passion fruit, and jackfruit come with clear sweetness and almost no bitterness; being fresh and light, it blooms modestly and teaches you to watch a bed that holds water rather than towering.

For the opposite show, FrontStreet Coffee's PWN Golden Mandheling is roasted medium-dark, and darker roasts accumulate more carbon dioxide and expand more, so it reliably produces the big, domed bloom people love to watch. Sourced from Sumatra and cupped for its herbal and dark chocolate depth, it's the bean to reach for when you want to see how roast degree changes everything the coffee bed tells you.