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Barista Technique:
Diagnosis of Extraction Problems

Espresso is mostly defined in terms of shot time and volume, since these are easiest to measure. By convention, the volume specifications for espresso are total volume, combining crema and liquid. The dwell time, the time it takes from turning on the pump to seeing the first drops of espresso emerge from the basket varies from machine to machine. So by convention, espresso extraction times are specified from the moment the pump is turned on.

I will specify the diagnostics in terms of shot ending color and volume, since these have the most intuitive correspondence to espresso taste. This means you should end the shot at the specified color, and then set the grinder to get the specified volume.


Volume Terms:

  • Ristretto range: 1 ounce to 1.5 ounce doubles. Compared to normales, the taste will be more intense and sweeter. Ristrettos usually have less crema.
  • Normale range: 1.5 to 2 ounce doubles.
  • Lungo range: 2 ounce to 3 ounce doubles. Compared to normales, the taste will be slightly milder and less sweet; with certain blends, the crema on a short lungo can be better than for normales.

Color Terms:

  • Dark stop: stopping the shot while the flow is still foamy and brown. Compared to a normal stop with the same volume, the taste will be slightly more intense, and balanced towards acidic.
  • Normal stop: stopping the shot as the flow goes from foamy and brown to more watery and tan. This point marks the optimum extraction amount of 20% of the coffee solids.
  • Light stop: stopping the shot sometime after the flow has become watery and tan colored. Compared to a normal stop at the same volume, the taste will be slightly less intense and balanced towards bitter.

Special Terms:

  • Optimum crema range: exact figures are basket dependent, but generally, normal to high flow rates are best. Typically 1.33 ounces dark-stopped to 2.25 ounces normal-stopped has the highest proportion of long lasting crema. Singles cannot extract at this flow rate, so tend to have less crema.
  • Start dump: initial few seconds of flow out of the portafilter, which is black and without crema, is allowed to go into the drip tray. The cup is inserted only as the flow gets brown and foamy.
  • Center cut: a start dumped and dark stopped shot.

Diagnosing the Taste and Appearance of an Extraction

Diagnostics means tasting the espresso and correcting its deficiencies by adjusting setup or extraction parameters. In a perfect world, correcting for one deficiency would never interfere with correcting for another. In the real world, there sometimes are conflicts, and you must prioritize. The highest priority goes to gross crema deficiencies, since these indicate that some parameter of the shot is well outside proper espresso range. The next priority is taste flaws that make a shot undrinkable. Finally, with these eliminated, you can work on fine-tuning everything to get the most harmonious taste.

Gross Crema Deficiencies

Gross deficiencies in the crema point to something far out of whack and have the highest correction priority. However, the blend itself may have unusually light, dark or thin crema; so when you notice these defects, taste the shot to confirm the problem.

  • Too light and large bubbles: If the shot is less than 20 seconds, re-read the last section and set the grinder properly. If the shot time/volume was correct, the machine is running drastically cold and requires immediate correction. The taste will be very thin and sour.
  • Almost black, or a black outer ring with tiny bubbles and thin crema: If the shot took forever to produce a few drops, reread the last section and correct the grind. Otherwise the machine is running drastically hot and needs immediate correction. The taste will be very bitter and burnt.
  • Good color, but thin and quickly dissipating: keep the extraction in the optimum crema range, especially with dark roasts, but usually it's old beans. Rarely, it can show a defective pump not developing sufficient pressure. In this case, the taste will be balanced, but weak and with a watery mouthfeel.

Taste Flaws

These taste flaws ruin the shot. Correcting them takes precedence over working on the taste balance.

  • Lemon peel: This can be a blending or roasting error and irreparable. Short term, start-dump the shot. Long term, set the temperature higher and make sure the grinder burrs are sharp. This flaw comes from fines of very high quality coffees, and good blends tend to flirt with it.
  • Metallic: Recently cleaned machines or brand new ones can have this. The taste is eliminated most quickly by flushing more after cleaning, or for new machines, pulling a lot of shots and dumping them. Dull burrs are another cause. Finally, a failure in the water treatment resulting in almost distilled, low mineral water will cause this.
  • 12 hours on the hot plate taste: Time to backflush and clean the portafilter. Verify the frequency of your cleaning schedule.
  • Instant coffee taste: The mark of overextraction. Grind coarser and stop darker, so volume stays the same. If the bitter taste is prickly-sharp rather than dull, also lower the temperature.
  • Thin and sourish: The mark of underextraction. Grind finer and stop lighter, so the volume stays the same. If the taste is extremely sour, also raise the temperature.
  • Salt or MSG: A common defect in Indonesian or slower roasted coffees, and difficult to correct. It is ameliorated by high crema content and sweet, ristretto shots, so dial-in exactly to 1.5 ounce, normal-stop color shots. If that fails, also start-dump, since the taste is slightly more concentrated there. Finally, strong flavors, particularly acidic ones, can cover the salt taste. Consider lowering the temperature to enhance these, if the blend's flavor balance permits. The best solution is to find higher quality Indonesians for the blend and/or speed up the roast finish.
  • Ashiness: Usually a flaw in rapidly dark roasted, low grown coffees. Drop the temperature to the low end of the espresso range. Dial in to the lungo end of the optimum crema range and dark stop the shot (you may be under 20 seconds when you do this, that's OK). These measures will not much reduce the ashiness, but will mask the problem with a little more brightness and crema. The real solution is to change blend.
  • Rubber or Iodine: Buying cheap coffee? This is the classic reason for start-dumping.
  • Sewage, decay, mold, sausage or cabbage smells: This is from badly fermented coffee. If the blend is normally good, it's from a stinker bean. Clean out the doser and burrs. If it keeps happening, there's nothing you can do except get new coffee. The importer slipped the roaster a bum bag, and the problem has to be resolved there.

Unbalanced Taste

When the crema is right and the shot has no taste flaws, you can fine-tune the setup and extraction to provide the most harmonious and balanced taste possible. Although everyone wants balanced taste, the exact combination of sweet, bitter and sours tastes that any person considers balanced is extremely variable. So these adjustments will be subjective; and there may be more than one optimum set up for the blend, especially if it is complex in taste.

  • Not sweet enough: Do more ristretto shots, grinding finer and stopping at the same color. This will take the shot out of the optimum crema range, so it has to be a good crema blend. You can also center cut the shots, however, this will reduce the distinctive flavors and can lead to blandness. On the other hand, somewhat bland center cut shots are good way to serve newcomers to straight espresso; or those who prefer more subtle flavors.
  • Over-intense flavors: Lower the pump pressure. If this is because there's not enough sweetness to balance the bitters and sours, use the previous fix. Also consider going more lungo with the same stop color.
  • Pallid Flavors: Raise the pressure. Also consider going more ristretto with the same stop color.
  • Overly sour: Raise the temperature. Short term, trying stopping lighter and grinding finer to keep the volume the same. If it's really bad, start-dump.
  • Overly bitter: Lower the temperature. Short term, try stopping darker and coarsening the grind to keep the volume the same.

Pursuing the Godshot

If you've never tasted great espresso, you may have read the last section and asked yourself how you can do all the diagnostics. You have good taste, otherwise I can hardly imagine how you've read this far. Good espresso isn't a punch in the mouth, but tastes wonderful. Expect that, trust your taste and judgment, and make the adjustments accordingly. Then taste the results. You'll improve very quickly.

To further develop that taste, it greatly helps to sample top flight espresso and get a feel for all its possibilities. Take every opportunity to visit good cafés and roasters, and try their espresso and blends. Ask the coffee people there what you are tasting and how to tell if it's right. Don't worry about getting bad information—it's a lot easier to recognize a good coffee person than a good coffee because their enthusiasm gives them away.

Empty cup You can go further by drinking top flight estate coffees brewed regularly and learning how the coffees from different places in the world vary. In comparison to wine and other gourmet items, coffee is the most economical of the truly great taste experiences. Deepen your appreciation even further by home roasting you own coffees and blending them for espresso, or taking part at tastings conducted by roasters.

There is a large variety of espresso equipment, and it's useful to know something of the possibilities. These are discussed in great detail on the coffee Internet sites (see the resources and the rest of this site). If this interests you, participate in these discussions. There are frequent get-togethers that are organized via these sites, so you will also get some hands on experience.

Espresso is a social world. If you want to turn this into a serious hobby, join the Specialty Coffee Association of America (SCAA), attend conventions and barista competitions, get to know others like yourself, as well as the stars of the business. If you like espresso and coffee, I guarantee you'll enjoy the activity and like the people you meet.

Finally, coffee is a big global business. It encompasses large numbers of very poor farmers whose livelihoods are frequently in the balance, a few very big businesses buying from them cheap and cutting quality, a mass public that doesn't know much about coffee except that it's a pick-me-up, and a group of enthusiastic drinkers and purveyors who love coffee. As enthusiasts, it's incumbent on us to convey to others how rewarding good coffee can be. If we don't understand the coffee trade and its issues, and if we don't foster a wider appreciation of good coffee, many farmers will suffer, some of the world's great coffees may disappear, and we will all be the poorer for it.

Frothing milk...