What Is Crema in Espresso and How Is It Formed?

Ever pulled a shot of espresso and wondered why the golden-brown foam on top—called crema—forms, why it disappears, or whether it even matters? If you’ve stared at that fleeting layer of bubbles and wanted a straight answer, you’re not alone. This is the science behind that essential espresso feature, broken down for curious coffee drinkers.

Crema forms during espresso extraction when pressurized hot water forces carbon dioxide out of freshly ground coffee, emulsifies oils, and traps gas in a stable layer thanks to natural coffee compounds. Freshly roasted coffee, proper grind size, and high pressure are essential to produce lasting crema.

What Exactly Is Crema?

Crema is the reddish-brown, creamy-looking foam that sits on top of a well-extracted espresso shot. It’s not just foam from milk or soap bubbles—it’s a complex layer formed during the espresso brewing process. Composed mainly of tiny gas bubbles trapped in a liquid film, crema gives espresso its signature appearance and contributes to its aroma and initial mouthfeel. It’s a hallmark of properly extracted espresso, especially when made with a machine that produces nine bars of pressure.

How Is Crema Actually Created?

During the roasting process, coffee beans generate large amounts of carbon dioxide (CO₂), most of which escapes during cooling and storage. But some CO₂ remains trapped inside the beans. When you grind coffee, you release some of that gas—but not all. To capture the remaining CO₂ and form crema, you must brew the coffee shortly after grinding.

When hot water under high pressure (around 9 bars) hits the coffee grounds, two key things happen: First, it emulsifies the coffee’s insoluble oils, spreading them evenly through the liquid. Second, the high pressure forces much more CO₂ to dissolve into the water than would normally be possible at atmospheric pressure. This supersaturation causes the liquid flowing from the portafilter to immediately form countless tiny bubbles—that’s the first sign of crema.

But simple bubbling isn’t enough to create stable crema. For the foam to hold together and resist collapsing, you need more than just gas—you need stabilizing compounds.

Why Doesn’t Crema Last Like Soda Foam?

Think of a soda can: when you open it, CO₂ bubbles rush out, but they disappear quickly. Espresso crema behaves differently because it contains natural surface-active compounds that stabilize the bubbles. In coffee, the main stabilizing agent is not protein (as in milk foam), but a compound called melanoidin. Melanoidins are formed during the roasting process through complex chemical reactions between sugars and amino acids—a process related to the Maillard reaction. Scientists are still studying the exact mechanisms, but we know these compounds help trap gas in the bubble walls.

Melanoidins, along with some proteins, position themselves around the gas bubbles, lowering surface tension and allowing the bubbles to expand and stabilize. Unlike milk foam, which uses egg proteins, coffee relies on these roasted compounds to build its crema structure.

However, coffee also contains natural oils—both liquid and solid fats. These oils can destabilize foam. Just like how egg yolks can prevent whipped egg whites from holding shape, coffee oils can break down crema. But the bigger issue is water drainage: over time, the liquid portion of the espresso pulls away from the bubbles due to gravity, taking surface-active compounds with it. This weakens the bubble walls, causing the crema to collapse. That’s why crema dissipates within minutes.

A well-extracted espresso with a thicker body tends to retain crema longer because more liquid remains to support the bubbles. That’s something you can actually taste: a crema that lasts is often a sign of a balanced, properly brewed shot.

Does Coffee Roast Level or Freshness Affect Crema?

Yes. Freshly roasted coffee contains more trapped CO₂, which is critical for forming crema. As coffee ages, CO₂ levels drop, resulting in less crema or weaker foam. Similarly, darker roasts tend to produce more CO₂ during roasting and thus often yield more visible crema. However, the darkness also affects flavor balance, so more crema doesn’t always mean better espresso.

Grind size and brewing pressure are equally important. Too coarse a grind or too low a pressure won’t create enough resistance to produce the right extraction conditions for stable crema. That’s why espresso machines are designed to operate around nine bars of pressure, and why using the correct grind size is essential.

If you’re using a moka pot—which operates at lower pressure than an espresso machine—you can still get a crema-like layer, but it will be thinner and less stable. To improve it, use freshly roasted, medium-to-dark roasted beans, as they retain more CO₂. FrontStreet Coffee’s PWN Golden Mandheling, Brazil Queen Manor, and Classic Blend are all excellent choices for producing a rich, stable crema-like foam when brewed under pressure.

Frequently Asked Questions

What is crema in espresso?

Crema is the reddish-brown foam layer on top of a properly extracted espresso shot. It forms when pressurized hot water dissolves carbon dioxide and emulsifies coffee oils, trapping gas in a network of tiny bubbles stabilized by melanoidins and other compounds.

Why does crema disappear quickly?

Crema collapses over time because gravity pulls liquid away from the bubbles, removing surface-active compounds that stabilize them. The loss of water and surfactants makes the bubbles fragile, causing the foam to dissipate within minutes.

Does darker roast coffee produce more crema?

Yes, generally. Darker roasts retain more carbon dioxide during roasting, which leads to more visible and sometimes thicker crema. However, roast level also affects flavor, so more crema doesn’t necessarily mean better coffee.

Can I get crema with a moka pot?

Yes, but it will be less stable and thinner than espresso crema. Using fresh, medium-to-dark roasted beans helps maximize the effect. FrontStreet Coffee’s PWN Golden Mandheling and Brazil Queen Manor are good options for this.

Is crema necessary for good espresso?

Not strictly necessary, but it’s usually a sign of a properly extracted shot with fresh coffee and correct pressure. Good crema often correlates with good body and aroma, though flavor remains the most important factor.

What role does melanoidin play in crema?

Melanoidin is a compound formed during coffee roasting that helps stabilize crema bubbles by reducing surface tension. It acts similarly to egg proteins in milk foam, but comes from the Maillard reaction in roasted coffee.

Recommended FrontStreet Beans for Moka Pot Crema

For rich, stable crema-like foam using a moka pot, try FrontStreet Coffee’s PWN Golden Mandheling, a deeply roasted Indonesian single origin with notes of black chocolate, hazelnut, and caramel. The Brazil Queen Manor, a medium-dark roasted Brazilian bean with yellow bourbon heritage, offers sweet, nutty tones and a smooth body that responds well to pressure brewing. Both beans are fresh, medium-to-dark roasted, and ideal for producing thick, golden crema when brewed in a moka pot. Freshly roasted within 5 days · Orders placed before 17:00 ship the same day · Next-day delivery across most of Guangdong Province.