Reading a shot — crema, body, and heart

Pulled into a clear glass, a well-made double presents three visible layers before they mix. Crema is the golden-brown foam on top, formed from tiny CO2 bubbles trapped in oils and roast compounds — its color and thickness are genuinely diagnostic: hazelnut-gold and tight-knit usually signals a fresh, well-extracted shot; pale and thin often points to under-extraction or beans past their best; dark, bubbled, and quick to collapse often points to over-extraction. Body is the caramel-brown middle layer, carrying most of the shot's sweetness and weight in the mouth.

Heart is the darkest, most concentrated base layer, carrying the bitterness and heaviest aromatics. Watching the pour itself is just as informative as reading the finished shot: it should start as slow, dark drips, build into a steady, even stream sometimes called the "mouse-tail," and gradually lighten ("blonde") toward the end — that blonding is the visual cue that the easily-extracted, sweeter compounds are mostly spent and it's time to cut the shot before pulling too far into bitterness.