All coffee guides · Troubleshooting
Dialling in espresso is easier when you change one variable at a time and work through a consistent decision tree. This checklist gives you a fast path from symptom to adjustment without needing to guess. The most common mistake is changing grind size, dose and temperature simultaneously — then not knowing which change fixed the problem. Work through this in order.
Before blaming grind size, confirm that everything else is consistent. Machine fully warmed up — allow at least 20-30 minutes for single-boiler machines. Dose consistent within 0.2g — use a scale, not a scoop. Distribution and tamping repeatable — same WDT pattern, same tamp pressure, level puck. Basket clean and dry. Portafilter fully locked in before starting. Grouphead flushed if using a saturated group. If any of these vary between shots, the grind size number is meaningless because you are not holding the other variables constant.
A shot that finishes in under 20 seconds for a standard 1:2 ratio is almost certainly under-extracted. The flow is too easy, meaning the grind is too coarse, the dose is too low, or the tamp is too light. Check tamp level first — an uneven tamp creates a fast channel. If tamp is fine, grind finer by one click or step and pull again. Do not change more than one variable per shot. Also check for channeling: a very fast shot with pale, watery appearance that then produces a dark second stream is channeling, not a grind problem — see the channeling section below.
A slow shot indicates the grind is too fine, the dose is too high, or the tamp is too hard. The most common cause is grind size. Grind coarser by one click or step. If you are using a high-dose, shorter-ratio recipe (like 18g in, 36g out in under 25 seconds), the grind needs to be finer overall — recalibrate your expectations if you have changed recipe. A slow shot that starts slow and gets faster during the pull (the flow accelerates noticeably) may indicate the bed is collapsing — check that the basket is not overfilled.
Sourness in espresso usually means under-extraction: not enough soluble compounds have been dissolved, leaving the sharper organic acids dominant in the cup. The fix is to extract more. Grind finer by one step. If the shot time is already long and the taste is still sour, increase temperature by 1-2 degrees. If the shot is within normal time range and finer grind causes channeling, improve puck preparation — channeling prevents even extraction and leaves sour pockets even when the average shot seems acceptable. Light-roast coffees taste brighter by nature, so some perceived sourness is normal and desirable. If you are brewing a dark roast and getting sourness, the most likely cause is grind size.
Bitterness in espresso usually means over-extraction: too many compounds have been dissolved, including the ones that taste harsh and astringent. Grind coarser by one step. If the shot time remains long after coarsening the grind, check dose — you may be overdosing for the basket. Also check temperature: machine temperature that is higher than needed pushes extraction up. If the taste is specifically dry and astringent (coating the tongue) rather than sharp bitter, this often indicates channeling has caused localised over-extraction in parts of the puck. Focus on puck prep before changing grind size further.
Channeling is when water forces a path through a weak point in the puck rather than flowing evenly through the coffee bed. Symptoms include: very fast initial flow followed by slowing, visible pale gushing followed by dark streams in a bottomless portafilter, uneven extraction marks on the spent puck, and a cup that tastes simultaneously sour and bitter. Fix channeling by improving puck prep, not grind size. Ensure the puck is level after dosing. Use WDT (Weiss Distribution Technique) to break up clumps. Tamp level and firm. If your basket has a burr on the edge, deburr it. If channeling persists across good puck prep, the basket or portafilter may have an alignment issue.
The first shot from a cold or under-warmed machine almost always tastes worse than subsequent shots. The grouphead, portafilter and basket absorb heat from the first shot, dropping water temperature significantly below the set boiler temperature. Solutions: extend the warm-up time, run a blank shot (water through the group with no coffee) immediately before the first real shot, or pre-heat the portafilter by locking it in for the full warm-up period. If your machine has a temperature surfing technique specific to its design, apply it. The second and third shots of the day are often the most reliable baseline for dialling in.
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