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Diagnosing an Improper Espresso Extraction
The bottomless portafilter dramatically shows the beauty of the extraction process; it reminds me of melted milk chocolate flowing into the cup. The contrasting colors, called tiger striping are excellent visual cues of a good extraction. Once settled in your cup, they form darker brown speckling and reddish-brown splotches on the surface of the crema referred to as mottling.
But not all pours are so attractive, as vividly demonstrated below. At one time or another, we've all seen this sort of shot. If you've used a bottomless portafilter, you may have even felt the spray of one of these shots!
So what's the problem and how do you correct it? Let's assume that the brew pressure and temperature are correct, the equipment is clean, you have a quality grinder, and the coffee beans are fresh. A quick checklist for diagnosing an improper extraction follows.
- Irregular pours?
Remember to dry the basket before dosing, and double-check the distribution is even. Verify the dispersion screen and water jet breaker is clean and clear. If the water in your area is hard and the machine hasn't been descaled regularly, check for scale build-up.
Too fast or too slow?
Correct the grind. If you own a Mazzer Mini, Cimbali Junior, or Macap grinder, check out the Feature Spotlight on Grinders for general hints on adjusting these three premium choices.
Old grinds in the dosing chamber?
Grinds dry out rapidly and extract much more quickly than fresh grinds. A mixture could create pockets of unevenness. Either run the grinder for a couple seconds and discard the first grinds exiting the chute since the last shot (when dosing by volume), or always brush the chute clear after grinding (when dosing by weight). Also remember to grind for couple seconds after changing the setting to clear the chute, and then empty the dosing chamber.
Uneven extraction, premature blonding?
Not enough coffee, uneven distribution, or canted tamp. Try overdosing (dose the portafilter until it is about three-quarter full, tap it gently on the grinder fork two times to settle the grinds, dose the remainder, then distribute and tamp as usual). Double-check that the tamp is level. Verify the dispersion screen is clear and water exits from it evenly.
Channeling from the edge?
This could be caused by too much tapping or rapping the side of the portafilter after the first tamp; consider a Staub tamping style. Another possibility is the top of the puck is grinding against the dispersion screen during the portafilter lock-in; verify there is adequate clearance to allow the puck to expand up to meet the dispersion screen.
Watching the extraction using a bottomless portafilter dramatically shows how the extraction is progressing, however one isn't absolutely required. Careful attention to the stream exiting the pour spout of a "normal" portafilter will show many of the same signs. Coloring will give you a clear idea when is the correct cutoff time, keeping in mind that tiger striping fades as the beans age. Also note that decaffeinated coffee stripes very little; it generally starts out darker and more uniform than the caffeinated equivalent and turns blond earlier. Of course, freshly roasted beans have more color striation during the pour too. Depending on the blend, four to ten days post-roast will give you the best results.
Although stopping the extraction when blonding ensues will generally get you the best shot possible for a particular extraction, correcting for an improper rate of extraction leads to the road of better espresso. If the extraction is too slow, the espresso may be bitter with a dark brown crema; if the extraction is too fast, the espresso tends to be sour and the crema uniformly cinnamon colored. Taste is your ultimate guide to correcting errors in grind, dosing, and temperature. Applied consistently, getting good shots is mostly a matter of technique.
