The role of Crema in espresso

If the cooking condition of espresso is Overestracted espresso, its crema color will be dark, and it will appear dark with a slightly black edge. On the other hand, if it is Under-extracted espresso, then the crema color is light, appears light golden yellow, and the texture is thin. Common examples are high cooking water temperature (above 93 degrees Celsius), slow flow rate, darker crema color, lower cooking water temperature (below 88 degrees Celsius), faster flow rate, lighter crema color. The higher the BrewingRatio of espresso, the darker the crema color, and vice versa. To put it simply, if you use more coffee powder, the smaller the espresso, the darker the crema will be. For example, Ristretto with 100% flush rate, its crema color is usually darker and must be darker than espresso with 50% flush rate. The espresso color with a relative flushing rate of 50% is also darker than the Lungo with a flushing rate of 33%. This is why many world flower draw champions (such as Yoshi Sawada) are accustomed to using triple filters to flush out more than 100% of the Ristretto as the subbase of the latte, because this can get the darkest background color and the most contrast effect.

The reasons for the disappearance of crema are grease / oil and gravity. When the surfactant dissolves in water, gravity pulls down the coffee material stored in the foam layer, which pulls the substance that covers the surface of the bubble, causing the bubble to become fragile and inelastic, and eventually burst quickly.

The speed at which the foam layer disappears mainly depends on the speed at which gravity acts. A cup of properly extracted concentrated surface foam will last longer than a cup of underextracted concentrate. This is because the overall composition of the correct extraction will be thicker, which can be confirmed by the tactile sensation concentrated in the mouth.