Espresso Basics: What is Crema

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The Science Behind Espresso Crema Formation

During the roasting process, coffee beans generate a large amount of carbon dioxide. Most of it dissipates during the cooling process, while a small amount remains trapped inside. Grinding releases these gases, so coffee must be prepared as soon as possible after grinding.

When hot water impacts coffee grounds under high pressure, it emulsifies the insoluble oils from the coffee grounds while simultaneously dissolving an excessive amount of carbon dioxide—far more than hot water can dissolve under normal atmospheric pressure. This is why countless tiny bubbles immediately appear when liquid flows from the portafilter. However, this alone cannot fully explain "Crema." Open a can of cola, and we can also see countless bubbles rising, but they simply cannot persist.

What is Espresso?

Espresso is a very small cup of coffee, typically finished in two or three sips. Its flavor is extremely intense, which many people find difficult to accept. The small serving size and intense flavor are reasons why espresso has limited popularity in China. However, when mixed with milk to make latte or with water to make Americano, it becomes very popular.

The appearance of espresso in a cup shows dark espresso liquid at the bottom with a layer of golden coffee oil floating on top. Is this coffee oil actually oil?

The Composition of Coffee Crema

We all know that peanut oil is extracted from peanuts, and dark roasted coffee beans secrete oil on their surface. So what constitutes that layer of oil extracted by espresso machines?

Italians call this top layer "Crema," and this unique, rich Crema can only be produced by espresso machines—the key lies in pressure. Espresso machines generate 9 bar water pressure to "squeeze" the coffee puck. Due to the excessive pressure, water becomes supersaturated with carbon dioxide, preventing its release and causing it to dissolve directly into the coffee liquid. During the extraction process, fats in the coffee are emulsified, and these fats encapsulate the carbon dioxide. Being lighter than water, they gradually separate, with golden oil floating to the surface—very visually appealing.

Achieving Perfect Crema

Therefore, this golden, delicate coffee crema is formed by insoluble coffee oils encapsulating carbon dioxide. So how can we make espresso have beautiful Crema?

According to FrontStreet Coffee, quality Crema appears golden, has a delicate surface, uniform color, shakes like cream with smoothness, and shows obvious "hanging" on the cup walls. It not only provides excellent visual appeal to espresso but also enriches mouthfeel and aroma when tasting, protects the coffee's flavor, and facilitates latte art fusion and pattern support when making hot milk coffee. Perhaps these are why people go to great lengths to pursue the perfect Espresso!

FrontStreet Coffee's Extraction Experience

Based on extraction experience, FrontStreet Coffee believes getting rich Crema is actually quite simple. First, when purchasing coffee beans, you need to select beans with high oil content and sufficient carbon dioxide, such as medium-dark roast beans within their tasting period (45-60 days), or fresh espresso blend beans containing a certain percentage of Robusta. For example, on FrontStreet Coffee's bean list, "Frontsteet Commercial Blend" and "Frontsteet Classic Blend" both produce beautiful crema easily precisely because they contain a small amount of Robusta beans.

When you've selected the right coffee beans, you still need to pair them with fresh grinding, stable high temperature, sufficient extraction pressure, plus reasonable extraction parameters. Satisfying these key factors is essential to get espresso rich with dense crema.

Analyzing Crema Quality

In summary, fresher beans, darker roast levels, and equipment with greater pressure and more stable performance result in better crema expression. Next, let's analyze specific situations—FrontStreet Coffee will teach you how to judge espresso quality by observing crema形态, thereby solving common extraction problems.

No Crema or Thin Crema

The problem likely lies in beans being stored too long (including improper storage and pre-ground coffee). The longer the storage time, the more gas exchange occurs between coffee beans and air, resulting in more carbon dioxide loss and ultimately less coffee crema. Additionally, insufficient machine pressure, low temperature, too coarse grind, insufficient tamping pressure... these are also causes of insufficient crema.

White-ish Crema

If your extracted espresso has good crema thickness but lacks golden color and the overall taste tends toward sharp acidity, it's likely because you used beans with too light a roast. For example, using hand-drip beans that primarily showcase fruity acidic flavors—like FrontStreet Coffee's washed Geisha—for espresso can easily result in unpleasant acidity and astringency due to under-extraction, accompanied by white-ish crema.

Coarse, Bubbly Crema

This type of espresso Crema usually lasts very short and dissipates quickly. This is caused by coffee beans being too fresh. Freshly roasted beans contain large amounts of carbon dioxide. When large amounts of gas are pressed into the coffee liquid, the emulsified oils cannot encapsulate the gas and easily break down.

Clumpy Crema

This type of espresso generally shows obvious "lumpy" consistency when shaken, with uneven surface crema and poor flowability—similar to over-foamed milk that's difficult to push and blend.

Important Notice :

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