The presence of crema, the foam on your espresso, means you are in the ballpark ... within range of having the variables of temperature, pressure, tamping, etc. under control. That is, unless your machine has a crema-enhancing attachment. But even then, you might still have honest crema, and you should be able to tell by "diagnosing" it. Crema is a part of the espresso beverage. Espresso is not meant to be all crema, nor should it have less than 1/10th crema. Crema is part of the visual lure of espresso, the aromatics, the mouthfeel, the flavor and long-lasting aftertaste or espresso. In its technical definition, crema is gas bubbles suspended in a liquid film, that has high "surface tension" between the water molecules. Crema should be compact and persistent: it should last 2 minutes before the suspended water molecules drain, the entrapped gas is released and the liquid underneath shows through.
Crema Diagnotics: Hopefully this chart will help a bit. Oftentimes, symptoms that appear in crema might be several problems and treating one cause will simply reveal another problem. Also remember that the taste of espresso trumps appearance (duh!) so if you have a 15 second shot with fading, light cream, but you love the flavor, to heck with how the crema looks!
|Is the crema a very light tan/yellow color? Did the extraction take under 15 seconds? (Light crema can also indicate low water temperature).
Solutions: Increase extraction time by grinding coffee finer, or tamping harder. And did you use enough coffee? Increase fineness of grind to extend extraction timeTemperature: Check water teamperature. Was the machine, the group, the coffee handle all warmed up properly? Unlikely but possible cause is that you homeroast, and the coffee is too fresh ... was the coffee rested long enough to degas? Many people prefer 48+ hours of resting after roasting for espresso use.
|Does the espresso have a very light tan dot in the middle of extremely dark crema color? 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?
Solutions: 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 color, 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?
Problem: Fast extraction, or light roast too.
Solutions: 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 color of tightly compacted foam? And/or does it have darker striations producing a "tiger skin" effect?
Solutions: This is how I like my espresso to look. But remember, espresso is a matter of taste and my "perfect espresso" might be a bit overextracter for some people. In Brazil they like a quick extraction time and a lighter roast than most of us West Coast Californians would prefer... to each their own. But when I see the modest amount of 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 ... I 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?
Problem: WAY Overextracted
Solutions: 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?
Problem: Grind too fine
Solutions: Make the grind coarser.
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. I cleaned a La San Marco for 2 days straight trying to remove the cause of my bitter espresso. 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.