Understanding Crema and Coffee Bean Oils

Crema forms when espresso is brewed under pressure. The 9-bar pressure of an espresso machine forces carbon dioxide from the coffee grounds into the liquid. At the same time, insoluble coffee fats become emulsified, wrapping around the gas bubbles. Because these fat-covered bubbles are lighter than water, they rise to the surface and create the golden layer known as crema. Without sufficient pressure, you cannot consistently produce this distinctive foam.

The oils on dark-roasted coffee beans are different from crema. These surface oils come from the beans themselves and appear as a sheen. When you wonder why does my coffee look oily or should coffee beans be oily, remember that visible oil on beans is normal for darker roasts and not the same as the emulsified fats in crema. Bean freshness, roast level, and extraction parameters affect crema quality.

The golden layer of crema on top of espresso, which Italians call Crema, is an important visual indicator for judging the quality of a cup of Espresso. It is not actual oil, but rather an emulsion layer formed by the insoluble fats in coffee wrapping around carbon dioxide, and it can only be consistently produced with the 9-bar pressure of an espresso machine. When the crema is missing, thin, pale, rough and full of bubbles, or clumpy, it often points to specific issues with bean freshness, roast level, equipment performance, or extraction parameters. Drawing on Front Street's extraction experience, this article sorts out the causes and evaluation criteria of Crema, helping you identify the root of the problem by observing the crema's appearance, so you can make an espresso with rich, dense crema.

What exactly is espresso? Simply put, it is a very small cup of coffee, usually finished in two or three sips. Its flavor is extremely intense, and many first-time tasters find it hard to get used to. The small cup size combined with the powerful taste is the main reason espresso has low acceptance in China. However, once milk is added to make a latte, or water is added to make an Americano, it immediately becomes a widely popular drink.

A shot of espresso in the cup looks like a deep black coffee liquid at the bottom, topped with a layer of golden coffee crema. So, is this layer of crema really oil?

Peanut oil comes from pressing peanuts, and the surface of dark-roasted coffee beans also exudes an oily sheen. So what exactly makes up that layer of crema on the surface of espresso extracted under high pressure by a coffee machine?

Italians call this substance "Crema." This rich and unique Crema can only be produced by an espresso machine, and the key lies in pressure. An espresso machine uses about 9 bar of water pressure to "squeeze" the coffee puck. Under tremendous pressure, the carbon dioxide in the grounds puts the water into a supersaturated state with respect to the gas. The carbon dioxide cannot escape and can only dissolve directly into the coffee liquid. At the same time, the extraction process also emulsifies the fats in the coffee. These fats wrap around the carbon dioxide, and because they are lighter than water, they gradually float upward and separate into layers, eventually forming a golden layer of crema on the surface with a rather captivating visual effect.

From this we can see that the golden, delicate coffee crema is actually the product of insoluble coffee fats wrapping around carbon dioxide. So how can you give espresso a beautiful layer of Crema?

In Front Street's view, high-quality Crema should be golden in color, with a delicate surface and even color. When gently swirled, it should be as smooth as cream, with a clear cling to the cup wall. It not only gives espresso an outstanding appearance, but when tasting it also adds layers of texture and aroma and helps protect the coffee's flavor; when making hot milk coffee, it also makes it easier to pour latte art and support the pattern. Perhaps it is precisely for this reason that people spare no effort in pursuing a perfect Espresso.

Based on past extraction experience, Front Street believes that achieving rich Crema is actually not complicated. First, when choosing coffee beans, priority should be given to beans with high crema richness and sufficient carbon dioxide content, such as medium-dark roasted beans within their optimal flavor period (45–60 days), or fresh espresso blend beans containing a certain proportion of Robusta. Taking FrontStreet Coffee's bean list as an example, the two espresso beans "Front Street Commercial Blend" and "Front Street Classic Blend" easily produce beautiful crema when pulled as espresso precisely because they include a small amount of Robusta.

After choosing the right beans, you also need to pair them with fresh grinding, stable high temperature, sufficient extraction pressure, and reasonable extraction parameters. Only when these key conditions are all met can you get an Espresso rich in dense crema.

Overall, the fresher the beans, the darker the roast, the greater the equipment pressure, and the more stable the performance, the better the coffee crema will present itself. Below we analyze one by one, as Front Street teaches everyone how to judge the quality of Espresso by observing the form of the crema, and thereby solve various common problems in extraction.

No crema at all, or very thin crema: The problem most likely lies in the beans having been stored too long, including improper storage methods and coffee beans having been ground into powder in advance. The longer they sit, the more fully the beans exchange gases with the air, the more carbon dioxide is lost, and naturally the less coffee crema appears in the final cup. In addition, insufficient coffee machine pressure, low temperature, too coarse a grind, and insufficient tamping force are also causes of too little crema.

Pale crema: If the extracted espresso crema has acceptable thickness but lacks a golden color and the overall taste is sharply acidic, it is very likely that lightly roasted beans were used. For example, using pour-over beans known for fruity acidity to make espresso can easily produce an unpleasant sourness and astringency due to underextraction, along with paler crema.

Rough crema with lots of bubbles: This type of espresso Crema often lasts only a very short time and dissipates extremely quickly. The reason is that the coffee beans are too fresh. Freshly roasted beans contain a large amount of carbon dioxide. When a large amount of gas is forced into the coffee liquid, the emulsified fats cannot completely wrap around it all, making it prone to collapse.

Clumpy crema: This kind of espresso usually shows obvious "lumps" when swirled, with an uneven surface of crema and poor fluidity, just like over-whipped milk foam that is difficult to spread and blend.

The above content is compiled by CoffeeHunters, a coffee news website.