Crema is the foam that forms on the surface of an espresso. Gas released during pressure brewing contributes to its appearance, alongside the coffee and the preparation. Its color, persistence and quantity can vary even between coffees that are enjoyable in different ways.
The source treats crema as a major diagnostic cue. It is worth observing, but a visual rule such as stopping whenever one color appears should not replace a measured recipe and tasting. A larger crema layer is not, by itself, evidence of a better espresso.
Record dose, beverage output, time and the coffee's age when comparing shots. Then assess sweetness, acidity, bitterness and texture in the drink itself. If the surface changes unexpectedly, check the underlying recipe and equipment condition rather than adjusting several settings solely to improve appearance. Crema is most useful as one piece of information within a consistent brewing process, not as a shortcut around evaluating the actual cup.
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