Crema is what distinguishes an espresso. This is the layer of foam that rests on top of the drink and is made up of proteins, oils and sugars, with bubbles of carbon dioxide (CO2) and water vapor. It intensifies the aromas, body, flavor and aftertaste of the coffee.
There are many variables to take into account to achieve a good crema: the bars of pressure used, the freshness of the bean, the grinding, the water temperature, the extraction time, the ratio, etc. Here we share five reasons why an espresso does not have cream.
The existence of the crema depends on how fresh the coffee being used to make the espresso is. The freshness of the coffee refers to how recently it has been roasted; ideally, less than one or two months beforehand. Roasted coffee can preserve the intensity of its flavors and aromas for that period of time, however it decreases over the weeks.
Older coffee will be partially oxidized and will not create as many melanoidins (sugars and amino acids), which are responsible for reacting with carbon dioxide and forming the tiny bubbles in the top layer of the espresso.
The type of machine and the pressure of the water jet are key to forming the crema. Espresso machines use bars, which are units that measure the pressure with which the water is heated and pushed through the machine to extract the coffee.
9 bars are needed to ensure that the CO2 formed in the beans during roasting emulsifies with the coffee properly when they are mixed with a pressurized jet of water at a high temperature, therefore successfully forming the crema.
For there to be a good layer of crema on the espresso, the coffee must be emulsified at the right temperature and pressure. Extraction time is also key; making a coffee in twenty seconds or in more than thirty seconds will influence the quality and existence of the crema.
The recipe also matters. It is recommended that 7 grams of finely ground coffee be brewed at 9 bars of pressure so that the water filters through at about 195 degrees Fahrenheit and produces a crema of approximately 3mm, which will result in 30ml of coffee being extracted.