For a long time, the appearance and quality of a crema coffee house – the thin layer of foam on top of an espresso cup – has been one of the standard features of an espresso. Traditionally, Perfect Crema is a shiny golden foam on top of a drinks house espresso cup, thick enough to hold a teaspoon of sugar for a few seconds before drifting to the bottom of the cup. If you’re fortunate, it will have tiger skin stripes – a patterned effect on Crema’s surface.
However, Crema is just a by-product of the extraction process, when the espresso machine creates a stream of water with tremendous pressure and eliminates CO2 and fat in the coffee.
Crema branded cup cannot tell you the quality of the coffee but will instead indicate the freshness of the coffee (coffee loses CO2 the longer it is stored, and therefore the Crema as it thins) and the degree of its roasting (the darker the roast, the more CO2 & fat will be produced, which means the thicker the Crema).
In short, a good espresso doesn’t necessarily make for the best Crema. As a result, the Crema class evaluation at the World Barista Championship is becoming less and less critical. Meanwhile, many other factors, such as the quality of the green coffee, the roasting process, and the extraction efficiency, are significant for the quality of the espresso.