Does Pour-Over Coffee Have Crema and Foam? What Does the Foam in Pour-Over Coffee Taste Like?

Careful observers may have noticed that when brewing coffee, a layer of foam floats on the surface of the liquid in the filter cup. The characteristics of this foam vary depending on the beans being used and the brewing time. Sometimes the foam is abundant, while other times it's quite sparse. It may appear brownish-yellow on some occasions, while at other times it might look whiter.

What Can Coffee Foam Tell Us?

What impact does coffee foam have on our brewing process? Or what brewing information can we derive from the state of the foam? Let's explore this with FrontStreet Coffee.

When pouring water after coffee blooming, golden foam emerges from the coffee grounds. This foam layer is primarily composed of carbon dioxide, oils, large coffee particles, and a small amount of fine powder. The main factor affecting the foam's color depth is the presence of large coffee particles.

In our daily coffee brewing, as we continue pouring water, the coffee foam gradually changes from deep yellow to light white. This phenomenon occurs because the large coffee particles floating on the surface gradually sink. The principle is quite simple: during blooming, most coffee grounds release gas, but not completely. Some larger particles have slower water penetration, so they require more time to release gas. When pouring water, these larger coffee particles float on the surface due to their light weight. Subsequent water pours wash these particles down, causing the foam color to become lighter.

Therefore, when pouring water, first flush out all the coffee bean foam, then determine the pouring range based on the depth of the foam color. For example, when pouring in only large circles, the foam in the center will be darker than that in the outer circle. When this situation is observed, you need to gradually reduce the pouring range to wash down the coarse coffee particles in the center. "The uniformity of foam color can also indicate the pouring situation."

Factors Affecting Foam Richness

When brewing different coffee beans, the richness of the foam varies considerably. Some coffees produce very rich foam, while others produce very thin foam, and sometimes foam voids even appear on the liquid surface. Two main factors affect foam richness: roast level and freshness.

Deep-roasted coffee beans have richer oils and carbon dioxide. Additionally, because the coffee texture is loose, coffee grounds easily float on the surface, resulting in richer foam. Lighter roasted coffee beans have relatively fewer oils and carbon dioxide, and the coffee beans have higher density, so fewer coffee grounds float on the surface.

When brewing some light roast coffees, after pouring water is complete, the foam on the coffee liquid surface gradually decreases as the liquid level drops. This is also a normal phenomenon. Thin foam adheres to the edges of the filter paper as the liquid level drops.

The richness of foam is also related to the freshness of coffee beans. Because foam is composed of coffee oils and carbon dioxide, when coffee beans have been recently roasted and are still very fresh, very rich foam will gush out during the water pouring after blooming.

When coffee beans have been stored for a long time, the carbon dioxide inside the beans has almost completely escaped, so the amount of foam released during brewing is relatively small.

Using Foam to Assess Coffee Quality

Therefore, in daily coffee brewing, we can judge the roast level of coffee based on foam performance. For example, when some coffee beans look similar in color and have similar taste descriptions, we can distinguish them by observing the richness of their foam. We can also determine the freshness of coffee beans, typically judged in combination with the degree of expansion during blooming. Additionally, we can adjust our pouring technique based on the state of the foam.