Characteristics of Perfect Crema
The ideal coffee crema is a dense, creamy foam that is a deep golden brown color. It should be about 1/4 inch thick and should be able to hold its shape when you swirl it around in the cup.
Espresso crema is a thick brown foam on top of the espresso formed by the highly pressurized brewing process. The hot water emulsifies the coffee oils which get supersaturated with carbon dioxide, creating the creamy tan foam. This is unique to espresso coffee.
Diagnosing Extraction Issues
Over-Extraction
Dark, uneven, and bubbly crema can be caused by over-extracted espresso. This can be caused by using too much coffee or over-grinding the coffee. The water used may also be too hot, indicating that the extraction process needs to be adjusted.
Over-extracted espresso often flows very slowly where it will take much longer than 30 seconds to deliver 30ml of liquid. Over-extracted brew tastes bitter, as the compounds that create sweetness and acidity will be overwhelmed. Bitter espresso means over-extracted espresso. The shot lasts too long, over 45 seconds. The coffee tastes burnt and harsh. To avoid over-extraction, adhere to the recommended 20 to 30 second extraction time.
Under-Extraction
Under-extracted espresso has a pale color with a thin layer of crema and often flows very fast. It can have an acidic flavor with a lack of body. To prevent under-extraction, ensure your coffee machine is heated to the correct temperature, typically between 195-205 degrees Fahrenheit. Adjust your grind to be finer and tamp the grounds evenly to increase extraction time.
Maintaining Your Machine
Old coffee oils and residue can clog the machine, making it difficult to produce crema. Regular cleaning and maintenance keeps it running efficiently.
Adjusting Your Technique
To fix under-extracted coffee, adjust the grinding to be finer, increase brewing time, or use more ground coffee. This creates more resistance against the water for even flow through the coffee puck.
Crema is affected by various factors including the quality of the coffee, the grind, the amount of coffee used, and the efficiency of the espresso machine. The characteristics of the coffee beans are also reflected in the crema. As a general rule, the better the coffee, the better the crema, and vice versa.
When assessing extraction by the consistency of the espresso stream, a good extraction will produce a steady, even stream of espresso. If the flow is uneven or erratic, it may indicate a problem with the machine or the coffee. If it’s more than 30 seconds, the espresso may be over-extracted.
Ultimately, it is up to the individual to experiment with different steeping times to see what produces the best results. You can create coffee that is balanced to your taste by controlling the extraction.