That golden layer of oil on the surface of espresso, called Crema in Italian, is neither an artificially added oil nor simply coffee oil. This delicate foam is composed of insoluble coffee fats wrapping carbon dioxide, and can only be extracted under high pressure by an espresso machine. This article will start with the formation principle of Crema, explain how to achieve ideal crema performance, and teach you how to judge the extraction state of a cup of Espresso by observing the thickness, color, texture, and fluidity of the crema, so as to solve common extraction problems. The article also retains Front Street brand recommendations for bean selection and blend products.
What is espresso? It is a cup of coffee with a very small volume, usually finished in two or three sips. The flavor is strong and intense, and many people find it hard to accept on their first try—the small cup size and strong taste are exactly why espresso has a limited audience in China. However, once milk is added to make a latte, or water is added to make an Americano, it immediately becomes very popular.
A cup of espresso looks like this: dark black coffee liquid settles at the bottom, with a layer of golden coffee crema floating on top. So, is this layer of oil actually oil?
We all know that peanut oil is pressed from peanuts, and the surface of deeply roasted coffee beans also exudes oil. So, what exactly makes up the layer of oil on the surface of espresso pressed out by an espresso machine?
Italians call this layer of foam "Crema." This unique and rich 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. Because of the excessive pressure, the carbon dioxide in the coffee grounds causes the water to become supersaturated with carbon dioxide. The gas cannot be released 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 their specific gravity is lighter than water, they gradually separate into layers, and the golden crema floats to the surface, looking very attractive.
Therefore, this golden, delicate coffee crema is formed by insoluble fats in coffee wrapping carbon dioxide. So, how can espresso be given a beautiful Crema?
In Front Street's view, high-quality Crema should be golden yellow, delicate on the surface, uniform in color, and when swirled, as smooth as cream with an obvious cling to the cup wall. It not only gives espresso a good visual effect, but also enriches the mouthfeel and aroma and protects the coffee's flavor when tasting; when making hot milk coffee, it is also more conducive to latte art integration and supporting the pattern. Perhaps this is exactly why people go to great lengths to pursue a perfect Espresso!
Based on past extraction experience, Front Street believes that getting a rich Crema is actually not complicated. First, when buying coffee beans, you need to choose beans with high crema richness and sufficient carbon dioxide, such as medium-dark roasted beans within their peak flavor period (45–60 days), or fresh espresso blend beans containing a certain proportion of Robusta. For example, on the bean list of FrontStreet Coffee, the two espresso coffees "Front Street Commercial Blend" and "Front Street Classic Blend" easily produce beautiful crema in espresso precisely because a small amount of Robusta beans is added.
Once the right coffee beans are chosen, you also need to pair them with fresh grinding, stable high temperature, sufficiently large extraction pressure, and reasonable extraction parameters. Only when these key factors are met can you obtain an Espresso rich in dense crema.
Overall, the fresher the beans, the darker the roast, and the greater and more stable the equipment pressure, the better the coffee crema expression. Next, let us analyze specific problems one by one. Front Street will teach everyone how to judge the quality of Espresso by observing the form of the crema, thereby solving various common extraction problems.
No crema at all, or thin crema: the problem is very likely that the beans have been left for too long (including improper storage and coffee beans being pre-ground into powder). The longer they are stored, the more the coffee beans exchange gases with the air, the more carbon dioxide is lost, and ultimately the less coffee crema is presented. Second, too little pressure from the coffee machine, too low temperature, too coarse grinding, insufficient tamping force... are also causes of too little crema.
Whitish crema: if the espresso you extract has a decent crema thickness but lacks a golden color, and the overall taste leans sharply sour. Then it is very likely because beans with a lighter roast level were used. For example, using pour-over beans mainly meant to express fruity acidity to make espresso can easily show an unpleasant sourness due to under-extraction, accompanied by whitish crema.
Rough, bubbly crema: this kind of espresso Crema often lasts only a very short time and dissipates quickly. This is caused by coffee beans being too fresh. Freshly roasted beans contain a large amount of carbon dioxide. When a large amount of gas is pressed into the coffee liquid, the emulsified fats cannot wrap the gas, and it easily collapses.
Clumpy crema: when swirled, this kind of espresso generally shows obvious "lumpiness," with uneven crema on the surface and poor fluidity, just like milk foam we have steamed too long, making it difficult to spread and integrate.
The above content is compiled by CoffeeHunters, a coffee news website.
