Espresso Troubleshooting Guide: Sour, Bitter, Fast, Slow and Uneven Shots

When a shot goes wrong, the fix is usually simple, but only if you check things in the right order. This guide starts from what you can taste or see in the cup and works back to the cause. It is written for café baristas, and it works just as well on a home machine.

Before you change anything: weigh the dose and the yield. Most “mystery” shots turn out to be a dose that drifted or a yield nobody measured. Fix the numbers first, then taste.

Quick diagnosis table

Check things in this order

Work from the cheapest and quickest check to the slowest. Most problems are solved in the first three steps.

1. Dose: is the basket getting the weight it was made for?
2. Yield: are you stopping the shot at a measured weight?
3. Grind: is the shot running in a sensible time for your ratio?
4. Puck preparation: are the grounds distributed and tamped level?
5. Cleanliness: when were the group, basket and portafilter last cleaned?
6. Beans: how old is the coffee, and has the bag been left open?
7. The machine: only now suspect pressure, temperature or a part. That is a job for your technician.

Espresso tastes sour

Sourness shows up straight away on the tongue and makes your mouth pucker. It means the water didn’t pull enough out of the coffee, which is called under-extraction.

Common causes

• Grind too coarse. Water runs through too fast. Seattle Coffee Gear flags shots that keep running under 20 seconds as a likely sign.
• Dose too low for the basket size.
• Water not hot enough. More common on small home machines than on commercial ones.
• Very fresh coffee that is still releasing a lot of carbon dioxide.
• A very light roast, which naturally tastes brighter and needs a finer grind or a longer ratio.

Fix it

1. Check the dose weight.
2. Grind finer in small steps, purging the grinder between shots.
3. If the time looks right and it still tastes sour, try a slightly longer ratio, such as 1:2.2 instead of 1:2.
4. If the beans were roasted in the last few days, let them rest a few more days.
5. If none of that helps, ask your technician to check the brew temperature.

Espresso tastes bitter

Bitterness shows up at the end of the sip and often leaves a dry feeling in the mouth. It usually means the water pulled out too much, which is called over-extraction.

Common causes

• Grind too fine, so the shot runs slowly. This is the most frequent cause.
• Dose too high for the basket.
• Shot run too long. Seattle Coffee Gear points to shots going well past 35 seconds.
• A dirty basket, portafilter or group head. Old coffee oils taste flat and bitter.

Fix it

1. Grind coarser in small steps.
2. If the time is fine and it is still bitter, stop the shot earlier for a shorter ratio.
3. Clean the basket, portafilter and shower screen.
4. If it still tastes burnt, ask your technician to check the brew temperature.

Dark roasts such as our Robusta and Kapeng Barako have a naturally bold, bitter edge. Some bitterness is part of their character, so judge the shot against the coffee, not against a light-roast Arabica.

Sour and bitter at the same time: channeling

If a shot tastes sharp and harsh at once, water is probably taking a shortcut through part of the puck. That part gets over-extracted while the rest is under-extracted. With a bottomless portafilter you may see one side turn pale before the other, or a thin spray shooting sideways.

• Break up clumps with a needle tool (WDT) and level the grounds before tamping.
• Tamp level. Pressing harder than about 30 pounds doesn’t compress the puck any further, according to Clive Coffee.
• Don’t overfill the basket so the puck touches the shower screen, and don’t underfill it either.
• Don’t knock the portafilter after tamping, and lock it in gently.

Our full guide to channeling goes deeper, and a puck screen can help on some machines.

Shot runs too fast

A shot that gushes out and hits your yield early will usually taste sour and thin. Check the dose first, because an underfilled basket runs fast at any grind. Then grind finer. If one shot runs fast and the next runs slow at the same setting, look at puck preparation and grinder clumping before you touch the grind again.

Shot drips or chokes

If the espresso only drips out, or the machine struggles to push water through, the grind is too fine or the basket is overfilled. Grind coarser and check the dose. If the shot still chokes after a big coarse adjustment, the shower screen or the basket holes may be blocked with old coffee, so clean them.

Weak or watery espresso

A shot can be well extracted and still taste weak if the ratio is too long. Stop the shot earlier, for example at 1:1.8 instead of 1:2.2. Also check the dose and the age of the beans. For drinks with a lot of milk, some cafés use a slightly stronger ratio so the coffee doesn’t get lost.

Little or no crema

Freshly roasted beans hold carbon dioxide, which is released during grinding and brewing and helps form the crema. As beans age, there is less of it, so older coffee gives less crema. Check the roast date and how the bag has been stored. A very fast shot can also look thin on top. Crema on its own doesn’t tell you a shot tastes good, so always taste.

Bitter no matter what you do with the grind

If grinding coarser doesn’t remove a flat, stale bitterness, the problem is probably coffee oil built up in the basket, portafilter, shower screen or group head. Backflush and soak the parts, following our espresso machine cleaning guide. Check the grinder too: old grounds stuck inside it can end up in your dose.

Each group pulls a different shot

On a multi-group machine, first make sure every barista uses the same dose, yield and tamp. Swap the baskets around, because baskets from different makers can behave differently. If one group is still consistently faster, slower or cooler than the others, it is time for a technician to check pressure and temperature. One commercial machine manual (Astoria) says the brew pressure gauge should read 8 to 9 bar while coffee is being made.

Keep shots consistent

• Dial in every morning and write the recipe at the bar. Our dial-in guide walks through it step by step.
• Weigh dose and yield on every shot during training, and spot-check during service.
• Keep bean bags sealed and use them in order of roast date.
• Clean the machine on a schedule, not only when shots go wrong.

Need beans for your bar?

We roast Robusta, CB’s Finest and an Arabica-Robusta Blend that cafés use for espresso and milk drinks. Cafés ordering 10 kg or more can see wholesale pricing.

Sources

• Seattle Coffee Gear: Why does my espresso taste sour or bitter?
• Clive Coffee: Dialing in espresso by taste
• Clive Coffee: What causes channeling in espresso
• Seattle Coffee Gear: How to avoid channeling
• Istituto Nazionale Espresso Italiano: Certified Italian Espresso parameters
• Astoria espresso machine user manual (pressure and dose checks)
• Coffee Chronicler: Crema explained