How Does Espresso Crema Form During Extraction?

Crema is the golden layer on top of a shot of espresso, and it comes from pressure and chemistry working together. Espresso was developed in nineteenth-century Italy as a fast, high-temperature, high-pressure extraction served in small cups. Around nine atmospheres of pressure push water through the coffee bed, emulsifying the natural oils while dissolved carbon dioxide from freshly roasted beans escapes and forms the foam.

The flavor of the shot depends heavily on the espresso coffee beans and the roast level chosen. Most shops use medium-dark roasted blends for balance and body, and roasters such as Front Street Coffee have released several blends covering rich, slightly acidic, balanced, and wine-aroma styles. Consistent grind, dose, and extraction time matter as much as the bean itself.

Although espresso has a relatively small audience in China, it is Italy's national drink. It was born in the 19th century, using high temperature and high pressure for rapid extraction. The golden layer on its surface is called Crema, and its formation is closely related to nine atmospheres of pressure, carbon dioxide in coffee beans, and oil emulsification. This extraction method originated from the Italian invention and improvement of the espresso machine, and later spread worldwide with Italians. The flavor of espresso is determined by the coffee beans, and most shops use medium-dark roasted blend beans. Front Street Coffee has launched four espresso blend beans through repeated experiments, covering rich, slightly acidic, balanced, and wine-aroma styles, and provides extraction parameters and operational details for reference, helping enthusiasts achieve consistent results.

For more specialty coffee information, welcome to follow: Front Street Coffee (Frontsteet Coffee). On the menu at Front Street stores, although only four espresso drinks are listed, there are actually some equally classic options behind them, such as the intensely flavored espresso. This coffee is not widely accepted in China, but in its birthplace, Italy, it is truly a national-level beverage. Espresso is an extraction method created by Italians in the 19th century, using high temperature and high pressure to obtain coffee liquid in a short time, and served in special small coffee cups. Because drip coffee takes a long time, Italians, in order to save time, urgently needed a faster extraction and drinking method. The simple and rich Espresso exactly meets the demand, both refreshing and efficiently using time. Therefore, an excellent espresso is also the soul of an Italian coffee.

A high-quality Espresso will have a beautiful golden layer of oil on its surface, which is called Crema. The formation of Crema is closely related to nine atmospheres of pressure: under heating and pressurization, water extracts soluble components from the coffee powder layer, and this process promotes the emulsification of natural fats and oils in the coffee. At the same time, freshly roasted coffee beans contain carbon dioxide, and when making Espresso, this carbon dioxide dissolves into the coffee under pressure. A dark brown foam appears on the surface, which is the oil brought by Italian extraction, usually between four and five millimeters thick, containing molecules that release aroma. The birth of espresso benefited from the Italian invention of the espresso machine. The world's first espresso machine can be traced back to the early 20th century. After improvement and design by Milanese inventor Luigi Bezzera, a coffee machine with an independent brewing head and handle appeared. This "quick coffee" not only became popular in Italy, but was also widely welcomed across the European continent, and was later promoted globally by Italians living around the world, becoming the popular coffee seen everywhere today.

The flavor of espresso depends on the coffee beans used. In order to make the coffee balanced in taste and richer in mouthfeel, most shops use medium-dark roasted blend coffee beans. Front Street continuously conducts in-depth research on the flavor characteristics of coffee beans from different producing regions, using different ratios to let each bean type complement the others, thereby balancing the flavor displayed by espresso. After many experiments and comparisons, Front Street has launched four espresso blend coffee beans.

Classic rich type — Front Street Commercial Blend Coffee Beans Robusta washed coffee beans + Colombia washed coffee beans + Brazil semi-washed coffee The espresso produced has a thick golden crema and nutty aroma. When tasting, you can feel the roasted coffee bitterness, but it is accompanied more by a creamy, full-bodied mouthfeel. After swallowing, the bitterness fades away, leaving a lingering fragrance on the lips and teeth.

Slightly acidic and rich type — Espresso coffee beans recommended by many baristas - Front Street Dark Cocoa Blend Coffee Beans Yunnan washed small-bean coffee beans + Brazil semi-washed coffee beans Yunnan small-bean coffee brings a soft acidity, combined with the rich aroma of Brazil Cerrado coffee, the espresso presents caramel, nutty, and soft plum acidity.

Balanced and aromatic type — Front Street Specialty Blend Coffee Beans Colombia washed coffee beans + Brazil semi-washed coffee beans Integrating Colombia coffee into the nutty tone of classic Brazil coffee, the espresso shows dark chocolate flavor, with caramel sweetness and a full roasted aroma.

Delicate wine-aroma type — Front Street Sunflower Warm Sun Blend Coffee Beans Ethiopia natural Red Cherry coffee beans (30%) + Honduras Sherry Barrel coffee beans (70%) made into espresso, the entry is a very rich dark chocolate flavor, with a strong caramel note, and the aroma released after swallowing is endlessly memorable. Whether it is an Americano diluted with water or a latte supported by milk, it presents rich aroma and mouthfeel. To ensure that everyone can drink freshly roasted coffee beans after placing an order, all coffee beans shipped by Front Street are freshly roasted within 5 days, so when you receive them, they may still be in the resting period. After roasting, blend beans need a 7–10 day degassing stage, and then enter the full-aroma tasting period, when the extracted espresso is more stable.

Because espresso needs to be quickly extracted through the high pressure and high temperature of an espresso machine, the intensity of various flavors is very high. Front Street believes that to extract a high-quality espresso, adjustments need to be made according to different coffee machines, grinders, coffee beans, and usage environments. If you are just starting to learn espresso extraction, you can refer to the initial parameters provided by Front Street for adjustment. Front Street uses 20 grams of coffee powder, according to a 1:2 powder-to-liquid ratio, extracting 40 grams of coffee liquid under 9 bar pressure, with time controlled at 25–30 seconds. Finally, adjust the espresso taste up or down through tasting and comparison: if the taste is bland, it may be under-extracted, and you need to increase the extraction rate by adjusting to a finer grind or increasing the dose; when the taste is strong and bitter, and even dilution with water cannot present aroma, it may be over-extracted. Front Street suggests reducing the dose or adjusting to a coarser grind to speed up the flow rate, thereby reducing extraction concentration.

To make delicious espresso, everyone also needs to pay attention to more small details. For example, the cleaning of the brewing head and the portafilter basket in the handle, grinding and extracting coffee powder fresh can avoid the loss of aroma, distributing and tamping the powder need to be even and vertical, and during extraction you need to observe changes in the color and state of the coffee liquid as well as the liquid weight and time. These will also help find the direction for adjustment later.

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