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Sour espresso is under-extraction: the water left before it could pull the sugars that balance coffee's natural acids. The fixes in order of likelihood: grind finer (the big one), let the machine actually heat up (five-plus minutes on thermoblock machines, longer on boilers, and preheat the portafilter), run the shot longer toward a 1:2 ratio in 25 to 30 seconds, and raise the temperature for light roasts. Sharp, lemony, thin, and gone-in-a-flash is the signature; if the same shot also turns harsh at the end, that is channeling doing both failures at once.
The diagnosis table
| Symptom | Cause | Fix |
|---|---|---|
| Sharp, lemony, thin | Under-extraction | Grind finer, extend toward 1:2 in 25-30s |
| Shot gushes fast and pale | Grind far too coarse or dose too low | Finer; weigh 18g in a double basket |
| First shot sour, later ones fine | Cold machine and portafilter | Heat 5+ minutes; run a blank shot to preheat |
| Light roast always sour | Temperature too low for the roast | Raise brew temp (92-96C); PID machines shine here |
| Sour start, bitter finish | Channeling | WDT, level tamp, bottomless portafilter to verify |
Why sour means "not enough," never "too much"
Extraction is a queue: bright acids dissolve first, sweetness second, bitterness last. A sour shot stopped in the first act, so every fix is some version of extracting more, finer grind for more contact area, longer ratio, hotter water. This is also why sour and bitter have opposite fixes and people who turn the wrong knob make it worse; the dial-in cheat sheet exists exactly for this, and an espresso scale turns "kind of sour" into numbers you can move. Track the fix shot by shot in the free Dial-In Logbook.
The two sour causes that are not the recipe
Cold equipment: thermoblock machines claim readiness before the group and portafilter are truly hot, and metal at 60C strips heat straight out of the brew water, so the first shot of the day runs effectively cooler, run a blank shot through the empty portafilter first. And beans: coffee roasted days ago or ultra-light roasts run sour on machines without temperature control, which is half the case for the PID mods in the Gaggia guide and the Silvia guide. The mirror-image failure lives in why is my espresso bitter.
Related reading
FAQ
What makes espresso taste sour? Under-extraction: the shot stopped before sweetness dissolved. Grind finer, run toward 1:2 in 25-30 seconds, and make sure the machine is fully hot.
Why is my first espresso of the day sour? Cold group and portafilter stealing heat from the water. Give the machine five-plus minutes and preheat the portafilter with a blank shot.
Is sour espresso the beans or the machine? Usually the recipe, sometimes temperature. Very light roasts want 94C+ that basic machines cannot hold, which is the classic case for a PID.
Never miss a cycle: the free one-page Machine Maintenance Calendar (PDF) puts every daily, monthly, quarterly, and yearly task for espresso machines, drip, Keurig, and moka pots on a card you can tape inside a cabinet.
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