The Science of Crema
The exact composition of espresso crema can vary depending on the coffee being brewed. Coffee origin, the roasting style implemented and the age of the coffee have the biggest roles to play and the presence of carbon dioxide, coffee oils, and water are the main factors that contribute to its unique characteristics.
Some of the main components of the crema include:
- Lipids: Oils and fats present in coffee beans contribute to the rich, creamy texture of the crema. These lipids emulsify during the brewing process, forming tiny droplets that help create the foam.
- Proteins: The proteins in coffee contribute to the formation of the crema as they denature and coagulate during the brewing process. They act as surfactants, helping to stabilize the foam and keep the emulsified oils and gases trapped within.
- Carbohydrates: The natural sugars and polysaccharides present in coffee beans contribute to the sweetness and body of the crema. Some of these sugars may also caramelize during the roasting process, adding to the flavor profile.
- Carbon dioxide: CO2 is a natural byproduct of the coffee roasting process and is trapped within the coffee beans. During the brewing process, the high pressure forces the CO2 out of the beans, forming small gas bubbles that contribute to the foaminess of the crema.
- Melanoidins: These are complex, brown-colored compounds formed during the roasting process as a result of the Maillard reaction, which is the chemical reaction between amino acids and reducing sugars. Melanoidins contribute to the color, flavor, and aroma of the crema.
- Organic acids: Coffee beans contain various organic acids, such as citric, malic, acetic, and quinic acids, which can impact the flavor and acidity of the crema.
- Aroma compounds: Various volatile compounds are responsible for the distinct aroma of espresso and its crema. These include aldehydes, ketones, esters, pyrazines, and furans, which are formed during the roasting and brewing processes.
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