The chart on the following page will assist in finding out symptoms that appear in crema. Treating one cause can sometimes reveal another problem.
The problems you cannot see:
Bad taste! Bitterness in espresso is a popular complaint. Before you blame the coffee, you need to make sure the machine is clean. A very bad, acrid bitterness results from machines/coffee handles that are dirty. A thorough cleaning of a neglected machine can be a considerable undertaking.
When the machine is clean, you should be able to do a dry-run with no coffee in the portafilter (meaning, run hot water into the cup through the coffee handle) … then let the water cool and taste it. If it tastes good, your machine should be clean.
|Is the crema a very light tan/yellow colour? Did the extraction take under 15 seconds? (Light crema can also indicate low water temperature).||Under Extraction
|Increase extraction time by grinding coffee finer, or tamping harder to increase extraction time. Did you use enough coffee? Check water temperature. Was the machine, the group, the coffee handle all warmed up properly? Did the coffee rest long enough to degas?|
|Does the espresso have a very light tan dot in the middle of extremely dark crema colour? Did it take 10 seconds for the first drops of espresso to appear? Did the espresso come out in drops, never becoming a stream? Did the extraction take over 30 seconds?||Over Extraction.
|Make the grind a little coarser, back off on the pressure when you tamp the coffee.
Did you use too much coffee?
The range is 7 to 11 grams per single espresso.
|Did the espresso have great crema colour, then visibly drop 1/4 inch or more in the cup as it sat for the first 1 minute? Was the surface of the espresso marked by very large, unstable bubbles in the crema? Is the crema pale?||Fast extraction, or light roast too.
|This might be a combination of short extraction and lighter roast. You will also get a less persistent crema if you use robusta in your blend … you have more crema perhaps but it fades sooner.|
|Does the crema have a rich dark colour of tightly compacted foam? And/or does it have darker striations producing a “tiger skin” effect?||None!
|This is how I like my espresso to look. But remember, espresso is a matter of taste. When you see dark speckling over substantial amounts of crema, tightly compacted and persistent crema, with perhaps a lighter swiggle in the middle from the last drops of the shot … You can anticipate something good.|
|Does the espresso have a thin crema with large oil globules? Did it take a really long time to produce 1 oz of liquid? Did it come out of the coffee handle one drop at a time?||WAY Over extracted
|Make the grind coarser, back off on the pressure when you tamp the coffee. Did you use too much coffee? The range is 7 to 11 grams per single espresso.|
|Does the espresso have grit in the cup after you finish?||Grind too fine
|Make the grind coarser.|
(Source: Sweet Maria’s Coffee Library- https://www.sweetmarias.com/library/content/espresso-almighty-crema)