When you order an espresso in a café, you might have observed a creamy, golden foam layer on top of your drink – that is the crema. The crema is an essential element of a properly brewed espresso and is commonly utilized as a visual sign of the coffee’s quality. But what exactly is the crema, and why is it important in espresso?
Crema is a combination of gases, oils, and colloids that forms on top of an espresso shot. It is produced when hot water is pushed through finely ground coffee beans at high pressure during the brewing process. The water extracts soluble and insoluble compounds from the beans, leading to the creation of crema.
Several factors contribute to the formation of crema, such as water pressure and temperature, grind size, coffee bean freshness, and the type of coffee machine. Espresso machines with high pressure and consistent brewing temperature are more likely to produce a creamy crema. 
Crema in espresso serves multiple important roles. It acts as a natural insulator, preserving the drink’s temperature and preventing it from cooling too quickly. Furthermore, crema includes aromatic compounds and oils that enhance the overall flavor and aroma of the espresso. These compounds are released when the crema is disrupted, intensifying the sensory experience of enjoying the espresso.
Additionally, crema contributes to the aesthetic appeal of espresso. A rich and consistent crema is typically a marker of a well-made espresso that has been properly extracted. The appearance and feel of the crema can give insight into the quality of the coffee beans and the expertise of the barista who made the espresso. Conversely, a thin or rapidly disappearing crema may indicate that the espresso was not brewed correctly, using either under-extracted, over-extracted, or old coffee beans.
The science behind the formation of crema is a complex process that involves various chemical and physical factors. When coffee beans are roasted, they undergo chemical reactions that produce volatile compounds like carbon dioxide, which are trapped in the beans. The high pressure during the brewing process forces these trapped gases to the surface of the espresso, creating bubbles that make up the crema.
Apart from gases, crema also includes oils obtained from coffee beans during brewing. These oils are combined with water and air to form a durable foam layer on top of the espresso. The presence of these oils enhances the espresso’s flavor, texture, and longevity of the crema.
Several factors can influence the quality of the crema on your espresso. These include the freshness and quality of the coffee beans, the size and distribution of the grind, the temperature and pressure during brewing, and the cleanliness of the espresso machine. For instance, using old or poorly stored coffee beans may produce a lackluster crema that appears dull and lacks flavor. Likewise, grinding the beans too coarsely or unevenly can result in a thin, weak crema that disappears quickly.
Baristas are essential in maintaining the quality and uniformity of crema in espresso. They must meticulously adjust the grind size, dose, and tamping pressure to achieve the perfect extraction for a rich and velvety crema. Baristas also must monitor the brewing time and temperature to avoid over-extraction or under-extraction, which can harm the crema.
Ultimately, crema is a crucial element in crafting a delicious espresso, enhancing its taste, scent, and appearance. The creation of crema involves a blend of chemical reactions, physical actions, and expertise from the barista, all working in harmony to achieve the ideal mix of gases, oils, and colloids. By comprehending the scientific principles behind crema and its impact on espresso’s excellence, coffee lovers can value and relish the craft of preparing a flawless espresso shot.
