Two tastes can have one cause
Dose, yield, and time summarize the shot. They cannot show whether some water moved too fast while other parts resisted it. That can make one cup taste both sharp and dry.
Spraying is a useful warning, not a lab measurement. A spouted portafilter can hide it. A bottomless portafilter can make small changes look dramatic. Use what you see with taste and repeatability.
Reset the preparation
Dry the basket. Spread the coffee evenly. Tamp level. Pull the same dose, yield, grind, and temperature setting. This makes preparation the only intended change.
If the next shot tastes more even, use it as your new starting point. If it still tastes sour and bitter without flow problems, check the coffee and recipe. Do not label the puck from taste alone.
- Keep the grind fixed.
- Use the same dose and yield.
- Change one preparation step you can repeat.
- Record if the shot is more consistent, not only prettier.
Finer is not always better
Research found that very coarse and very fine settings can both give lower and less repeatable extraction under the tested conditions. This does not identify your grinder setting. It does show why finer is not always safer.
Fix a shot puts the preparation check first when the signs conflict. It cannot detect channeling from taste or flow labels.
Guide limits
This guide uses your measurements and observations. It does not test your equipment.
Enter your shot. Get one next step.
Fix a shot fills in this guide's taste, flow, and time pattern. Replace them if they do not match your shot. Enter the dose and yield from your actual shot, then check every field before you continue.
Open Fix a shot with this symptom →Common questions
Does sour and bitter prove channeling?
No. It is a reason to check even flow, not proof of channeling. Coffee, water, temperature, cleanliness, and taste can also cause these notes.
Should I use a bottomless portafilter?
It can make some flow problems easier to see, but it is not required. Taste and repeatability still matter.
What should stay the same?
Keep dose, target yield, grind, and temperature the same while you improve spreading and tamping.
Sources and their limits
- Peer-reviewed researchSystematically Improving Espresso: Insights from Mathematical Modeling and ExperimentMatter / University of Huddersfield research portal · checked 2026-07-22(opens in a new tab)
Supports the nonuniform-flow warning at very fine settings; it does not diagnose an individual puck.
- Practical guideThe Espresso CompassBarista Hustle · checked 2026-07-22(opens in a new tab)
Supports separating strength, extraction, yield, and evenness; it remains a practitioner framework rather than an individual measurement.