Fix My Coffee
What is wrong with this cup? Name the symptom, check the suspects in order, then change one variable in a controlled experiment.
When a cup tastes wrong, the most common mistake is changing several things at once: new beans, a finer grind, hotter water. The next cup is better — and you have no idea which change did it.
This page does not hand you an answer. It walks you through a diagnosis: name what is wrong, see which variables might cause it, then change exactly one variable and brew a comparison cup. Log it in the Brew Log, and decide on the next suspect after that cup.
Step by step
- Symptom
- Suspects
- Experiment
1. What is wrong with this cup?
Pick the closest one. Confirm the symptom before changing anything.
Every symptom at a glance
The same diagnosis table as plain text: every symptom, every suspect and its one experiment, ready to expand.
Sour, sharp, thin · Like lemon water; a sharp sourness that vanishes fast
Bright, sweet fruit acidity is not a fault. Sharp, short and sweetless — with nothing left after you swallow — is the sourness of under-extraction.
Suspect 1: GrindParticle Size Distribution → Extraction → Sensory Perception
Particles are too coarse, so water only took the fast-dissolving acids; sweetness and body stayed in the grounds.
Experiment: change only「Grind · Finer」: Same coffee, ratio and temperature — grind two steps finer and nothing else.
Keep the same: Bean, Water, Temperature, Ratio, Technique
If it is this: The sharp sourness rounds out and sweetness appears; drawdown slows a little.
Read: Chapter 20 · Grind SizeChapter 23 · ExtractionMatching real lab: Grind Experiment
Suspect 2: TemperatureTemperature → Extraction → Sensory Perception
Cooler water dissolves more slowly. Light roasts especially need heat, and water left to sit after boiling often drops below 90 °C.
Experiment: change only「Temperature · Hotter」: Keep the recipe; use the water right off the boil (about 93–96 °C). Only the temperature changes.
Keep the same: Bean, Water, Grind, Ratio, Technique
If it is this: Less sourness, more sweetness and a longer finish.
Read: Chapter 24 · The Five Major Brewing VariablesChapter 23 · ExtractionMatching real lab: Temperature Experiment
Suspect 3: TimeTime → Extraction → Sensory Perception
Contact time was too short for extraction to finish. In immersion brewers you can simply wait longer; in pour-over, time follows the grind — check grind first.
Experiment: change only「Time · Longer」: Immersion brew: same coffee, water and temperature — steep one extra minute before filtering.
Keep the same: Bean, Water, Temperature, Grind, Ratio
If it is this: Sweeter and fuller; the acidity steps back.
Read: Chapter 24 · The Five Major Brewing VariablesChapter 28 · Immersion Brewing
Suspect 4: RoastRoasting → Extraction → Sensory Perception
Very light roasts are harder to extract and naturally more acidic. If the cup is still sour after the others, it may be the coffee itself.
Experiment: change only「Roast · Darker roast」: Same recipe, a slightly darker-roasted coffee; everything else as before.
Keep the same: Water, Temperature, Grind, Ratio, Technique
If it is this: Clearly less acidity; more caramel and cocoa notes.
Read: Chapter 15 · Light, Medium, DarkChapter 16 · Roast Changes Flavor
Bitter, harsh, burnt · Harsh bitterness; an aftertaste like char or medicine
A sweet, dark-chocolate bitterness is normal. Investigate the harsh kind that clings to the back of the tongue and gets worse as you drink.
Suspect 1: GrindParticle Size Distribution → Extraction → Sensory Perception
Particles are too fine; the extra surface area lets water pull out the late, bitter compounds too.
Experiment: change only「Grind · Coarser」: Same coffee, ratio and temperature — grind two steps coarser and nothing else.
Keep the same: Bean, Water, Temperature, Ratio, Technique
If it is this: Less bitterness and harshness, a cleaner cup; drawdown speeds up a little.
Read: Chapter 20 · Grind SizeChapter 23 · ExtractionMatching real lab: Grind Experiment
Suspect 2: TemperatureTemperature → Extraction → Sensory Perception
For darker roasts, boiling water is too aggressive: the bitter compounds dissolve fast and in quantity.
Experiment: change only「Temperature · Cooler」: Keep the recipe; only drop the water to 85–88 °C (let it sit two or three minutes after boiling).
Keep the same: Bean, Water, Grind, Ratio, Technique
If it is this: The bitterness softens and sweetness becomes easier to find.
Read: Chapter 24 · The Five Major Brewing VariablesMatching real lab: Temperature Experiment
Suspect 3: RoastRoasting → Sensory Perception
Burnt bitterness may come from the roast rather than the brew: a dark roast stays bitter whatever the recipe.
Experiment: change only「Roast · Lighter roast」: Same recipe, a lighter-roasted coffee; everything else as before.
Keep the same: Water, Temperature, Grind, Ratio, Technique
If it is this: If the burnt note disappears, the problem was the roast, not your brewing.
Read: Chapter 15 · Light, Medium, DarkChapter 16 · Roast Changes Flavor
Suspect 4: TimeTime → Extraction → Sensory Perception
Steeped too long, extraction overshot. Most common in immersion; for a slow pour-over, check grind and pouring first.
Experiment: change only「Time · Shorter」: Immersion brew: everything the same, filter one minute earlier.
Keep the same: Bean, Water, Temperature, Grind, Ratio
If it is this: Less bitterness; if it turns sour, the old time was closer to right.
Read: Chapter 24 · The Five Major Brewing VariablesChapter 28 · Immersion Brewing
Flat, hollow, lifeless · Tastes of coffee but empty in the middle; not sour, bitter or sweet
Unlike “too weak”: the strength is there, but the flavor is flat, without sweetness or aroma.
Suspect 1: BeanFreshness → Flow & Resistance → Extraction → Sensory Perception
Stale coffee has lost its aromatics and barely blooms. Most common a month or two after roasting, or with pre-ground coffee.
Experiment: change only「Bean · Use fresher beans」: Same recipe with a bag roasted two to four weeks ago, ground just before brewing.
Keep the same: Roast, Water, Temperature, Grind, Ratio, Technique
If it is this: The bloom rises clearly; aroma and sweetness come back.
Read: Chapter 17 · Freshness and DegassingChapter 18 · How to Store Coffee
Suspect 2: WaterBrewing Water → Extraction → Sensory Perception
Water with almost no minerals (distilled or heavily purified) carries fewer flavor compounds out, so the cup tastes flat.
Experiment: change only「Water · More minerals」: Same recipe; swap purified water for a moderately mineralized bottled water (about 50–150 mg/L total dissolved solids on the label).
Keep the same: Bean, Temperature, Grind, Ratio, Technique
If it is this: A more dimensional cup; sweetness and acidity both clearer.
Read: Chapter 21 · Coffee and WaterMatching real lab: Water Experiment
Suspect 3: TechniqueAgitation → Extraction → Sensory Perception
Water ran through only part of the bed (channeling): some grounds were barely extracted, others over-extracted, and together they taste hollow.
Experiment: change only「Technique · More agitation」: Keep the recipe; only stir the bloom gently with a spoon so every particle gets wet.
Keep the same: Bean, Water, Temperature, Grind, Ratio
If it is this: Sweetness appears in the middle; the cup feels complete.
Read: Chapter 27 · Pour-overChapter 24 · The Five Major Brewing Variables
Weak, watery · Pale, tastes like it was watered down
Weak is about strength: the flavor is right but there is not enough of it. If it is also sour and thin, start with “sour”.
Suspect 1: RatioBrew Ratio → Strength → Sensory Perception
Too much water for the coffee. Strength is set first by the ratio — and scoops drift a lot.
Experiment: change only「Ratio · Stronger (more coffee or less water)」: Use a scale: same water, 10% more coffee (e.g. 15 g → 16.5 g), same grind.
Keep the same: Bean, Water, Temperature, Grind, Technique
If it is this: Stronger and heavier, with the same flavor direction.
Read: Chapter 22 · Brew RatioMatching real lab: Ratio Experiment
Suspect 2: GrindParticle Size Distribution → Extraction → Strength → Sensory Perception
The dose is fine but the grind is too coarse: less dissolves, so the strength stays low.
Experiment: change only「Grind · Finer」: Same dose, water and temperature — grind one or two steps finer.
Keep the same: Bean, Water, Temperature, Ratio, Technique
If it is this: A bit stronger and sweeter; if it turns bitter, go back half a step.
Read: Chapter 20 · Grind SizeChapter 23 · ExtractionMatching real lab: Grind Experiment
Suspect 3: TemperatureTemperature → Extraction → Strength → Sensory Perception
Cool water extracts less, so the cup is weaker too.
Experiment: change only「Temperature · Hotter」: Same recipe, water straight off the boil.
Keep the same: Bean, Water, Grind, Ratio, Technique
If it is this: Strength and sweetness both rise a little.
Read: Chapter 24 · The Five Major Brewing VariablesMatching real lab: Temperature Experiment
Too strong, heavy · Heavy on the tongue, cloying after two sips; you want to add water
Strong is not the same as bitter: if the flavor is right but there is too much of it, it is a strength problem.
Suspect 1: RatioBrew Ratio → Strength → Sensory Perception
Too much coffee for the water. It is the most direct dial — turn it first.
Experiment: change only「Ratio · Weaker (more water or less coffee)」: Same dose, 10–15% more water (e.g. 1:15 → 1:17), same grind.
Keep the same: Bean, Water, Temperature, Grind, Technique
If it is this: Lighter, with flavors easier to tell apart.
Read: Chapter 22 · Brew RatioMatching real lab: Ratio Experiment
Suspect 2: GrindParticle Size Distribution → Extraction → Strength → Sensory Perception
A very fine grind extracts more and raises strength — usually with some bitterness.
Experiment: change only「Grind · Coarser」: Same ratio and temperature — grind one or two steps coarser.
Keep the same: Bean, Water, Temperature, Ratio, Technique
If it is this: Lighter and cleaner.
Read: Chapter 20 · Grind SizeChapter 23 · ExtractionMatching real lab: Grind Experiment
Dry, astringent · Tongue and gums feel tight afterwards, like strong tea or an unripe persimmon
Astringency is a texture (drying, tightening), not a taste. It can come with bitterness or on its own.
Suspect 1: GrindParticle Size Distribution → Extraction → Sensory Perception
Too many fines: the smallest particles over-extract, adding astringency and clogging the filter.
Experiment: change only「Grind · Coarser」: Everything the same, grind one or two steps coarser so there are fewer fines.
Keep the same: Bean, Water, Temperature, Ratio, Technique
If it is this: Less of the tight feeling; a cleaner finish.
Read: Chapter 20 · Grind SizeChapter 19 · Why We Grind CoffeeMatching real lab: Grind Experiment
Suspect 2: TechniqueAgitation → Extraction → Sensory Perception
Pouring hard or swirling vigorously at the end drives fines to the bottom and over-extracts them.
Experiment: change only「Technique · Less agitation」: Same recipe; make only the last pour gentle and slow, with no stirring or swirling.
Keep the same: Bean, Water, Temperature, Grind, Ratio
If it is this: Less astringency and a smoother drawdown.
Read: Chapter 27 · Pour-overChapter 24 · The Five Major Brewing Variables
Suspect 3: TemperatureTemperature → Extraction → Sensory Perception
With darker roasts, very hot water also pulls out the astringent compounds.
Experiment: change only「Temperature · Cooler」: Same recipe, water 4–5 °C cooler.
Keep the same: Bean, Water, Grind, Ratio, Technique
If it is this: A rounder mouthfeel.
Read: Chapter 24 · The Five Major Brewing VariablesMatching real lab: Temperature Experiment
Muddy, murky, unclear · Flavors blur together; there is sludge at the bottom of the cup
A French press is naturally heavier and a little silty compared with paper filters. This is about flavors so blurred you cannot tell them apart.
Suspect 1: GrindParticle Size Distribution → Extraction → Sensory Perception
Too fine a grind, or too many fines: the silt gets through the filter and keeps extracting in the cup.
Experiment: change only「Grind · Coarser」: Everything the same, grind two steps coarser.
Keep the same: Bean, Water, Temperature, Ratio, Technique
If it is this: Less sludge; flavors separate.
Read: Chapter 20 · Grind SizeChapter 28 · Immersion BrewingMatching real lab: Grind Experiment
Suspect 2: TechniqueAgitation → Extraction → Sensory Perception
Too much stirring or swirling suspends the fines in the liquid.
Experiment: change only「Technique · Less agitation」: Same recipe; only drop the mid-brew stirring. With a French press, let it settle a minute, press gently and leave the last sip.
Keep the same: Bean, Water, Temperature, Grind, Ratio
If it is this: Clearer, with a cleaner finish.
Suspect 3: WaterBrewing Water → Extraction → Sensory Perception
Very hard water (the kind that scales your kettle) can make a cup taste dull and muted.
Experiment: change only「Water · Fewer minerals」: Same recipe; swap tap water for filtered or a lower-mineral bottled water.
Keep the same: Bean, Temperature, Grind, Ratio, Technique
If it is this: Brighter and cleaner.
Read: Chapter 21 · Coffee and WaterMatching real lab: Water Experiment
Different every day · Great yesterday; the same routine today tastes wrong
Do not tweak the recipe yet: if a variable is drifting on its own, no adjustment will stick. Pin it down first.
Suspect 1: RatioBrew Ratio → Strength → Sensory Perception
Scooping coffee and pouring by eye easily drifts the ratio by 10–20% from day to day.
Experiment: change only「Ratio · Weigh it every time」: For the next three cups, weigh both coffee and water every time; do everything else as usual.
Keep the same: Bean, Roast, Water, Temperature, Grind, Time, Technique
If it is this: If the three cups converge, the problem was measuring.
Read: Chapter 22 · Brew RatioMatching real lab: Ratio Experiment
Suspect 2: TemperatureTemperature → Extraction → Sensory Perception
How long the kettle sits after boiling varies, and 5–10 °C differences are common.
Experiment: change only「Temperature · Same temperature every time」: For the next three cups, wait the same time after boiling (or use a thermometer); everything else as usual.
Keep the same: Bean, Roast, Water, Grind, Ratio, Time, Technique
If it is this: Cup-to-cup differences shrink.
Suspect 3: BeanFreshness → Flow & Resistance → Extraction → Sensory Perception
The same bag keeps changing: lots of gas just after roasting, then slowly fading — faster once opened.
Experiment: change only「Bean · Keep days-off-roast steady」: Split a bag into single-brew portions, seal them (freezing is fine) and take one each time; same recipe.
Keep the same: Roast, Water, Temperature, Grind, Ratio, Time, Technique
If it is this: More stable flavor across the week.
Read: Chapter 17 · Freshness and DegassingChapter 18 · How to Store Coffee
Suspect 4: TechniqueAgitation → Extraction → Sensory Perception
Pour speed, number of pours and bloom time done by feel all vary — total drawdown time gives it away.
Experiment: change only「Technique · Same technique every time」: Write down a fixed pour schedule (how many grams at what time) and follow it with a timer for three cups.
Keep the same: Bean, Roast, Water, Temperature, Grind, Ratio, Time
If it is this: Total time within 15 seconds, and the flavor steadies with it.
Read: Chapter 27 · Pour-over
Slow drawdown, clogged · Water pools in the dripper; still dripping after five or six minutes
A typical single-cup pour-over finishes in about 2:30–4:00. Much slower usually also tastes bitter and dry.
Suspect 1: GrindParticle Size Distribution → Flow & Resistance → Time
Fine particles leave tiny gaps in the bed, so water cannot pass — and fines clog the paper.
Experiment: change only「Grind · Coarser」: Same ratio, temperature and pouring — grind two steps coarser.
Keep the same: Bean, Water, Temperature, Ratio, Technique
If it is this: Clearly shorter drawdown; less bitterness and dryness.
Read: Chapter 20 · Grind SizeChapter 27 · Pour-overMatching real lab: Grind Experiment
Suspect 2: TechniqueAgitation → Flow & Resistance → Time
Too much stirring or swirling sends fines to the bottom, where they form a layer of “mud” on the paper.
Experiment: change only「Technique · Less agitation」: Same recipe; drop the stirring and swirling and pour a thin stream in the center.
Keep the same: Bean, Water, Temperature, Grind, Ratio
If it is this: Smoother drawdown and a flatter bed.
Read: Chapter 27 · Pour-over
Suspect 3: BeanFreshness → Flow & Resistance → Time
Coffee only days off roast releases a lot of gas, which pushes back on the water and makes drawdown slow and uneven.
Experiment: change only「Bean · Rest it longer」: Let the same bag rest a few more days (brew one to two weeks off roast); same recipe.
Keep the same: Roast, Water, Temperature, Grind, Ratio, Technique
If it is this: The bloom calms down and drawdown time returns to normal.
Fast drawdown · The water runs straight through; done in just over a minute
Much faster than the usual 2:30, with a cup that is both sour and weak.
Suspect 1: GrindParticle Size Distribution → Flow & Resistance → Time
Coarse particles leave big gaps; water passes through the bed with almost no contact.
Experiment: change only「Grind · Finer」: Same ratio, temperature and pouring — grind two steps finer.
Keep the same: Bean, Water, Temperature, Ratio, Technique
If it is this: Longer drawdown, less sourness and weakness.
Read: Chapter 20 · Grind SizeChapter 27 · Pour-overMatching real lab: Grind Experiment
Suspect 2: TechniqueAgitation → Flow & Resistance → Time
Pouring all the water at once, or along the filter wall, lets it bypass the bed.
Experiment: change only「Technique · Change the pour pattern」: Same recipe; split it into three or four pours in small circles around the center, avoiding the paper.
Keep the same: Bean, Water, Temperature, Grind, Ratio
If it is this: Longer drawdown and a sweeter cup.
Read: Chapter 27 · Pour-over