The cup is sour and the bed looks innocent

[Civic Fish Stories]

Brewer and filter: Hario Switch 03; Hario 03 paper
Grinder, burr and calibration: Timemore C3; S2C conical burr; 18 clicks
Bean, roaster, process and roast date: Ethiopia Bombe; SEY Coffee; natural; roast date 2026-08-19
Dose and water mass: 16.0 g coffee; 272 g water
Temperature and water profile: 96°C; Lotus-style remineralized distilled water, moderate hardness / low alkalinity
Pour/agitation schedule: 60 g bloom for 45 s, then pulse pours roughly every 30 s to 272 g
Drawdown time: 3:20
Expected and perceived flavour: expected clean citrus and tea-like finish; perceived cup is bitter in the finish
Changes already tested: tested 2°C lower water temperature; same grind and pouring schedule

I had this working two brews ago and now I am getting the problem in the title. I wrote the numbers down because otherwise I know we will spend ten replies discovering I changed three things at once. What would you change first?

[Civic Fish Stories]

I tested one change from the opening post and it moved the cup, but did not finish the job. Next variable: extend the bloom by 15 seconds. Why: this coffee may still be releasing enough gas to disturb the early extraction. Expected result: more even early flow and a sweeter cup as it cools. I will report the actual result rather than stack another change on top.

[Wire And Gloves]

i’ve used Ethiopia Bombe on the same Hario Switch 03 / Timemore C3 combination. Change: increase dose by 0.5 g while keeping water fixed. Why: the last part of the brew may be adding dryness without useful sweetness. Expected result: a clear change in flow speed if the paper is part of the problem. Keep everything else exactly where it is for one brew

[Dhrupad Notes]

Same Hario Switch 03 and grinder here, different but similarly light coffee. Change: change only the filter paper. Why: this coffee may still be releasing enough gas to disturb the early extraction. Expected result: less bitterness in the last third of the cup. That should tell you whether the behaviour belongs to the setup rather than this exact bag.

[Coffee-Kriti]

Controlled-test suggestion: use the same water but shorten the main pour. Why: the present agitation can be creating fines migration and choking the bed. Expected result: more even early flow and a sweeter cup as it cools. Do two brews if you have enough coffee, one current recipe and one changed variable, and taste them side by side as they cool.

[Wing Chun Wrench]

One variable only: extend the bloom by 15 seconds. Why: paper speed is an easy hidden variable to rule out before blaming the grinder. Expected result: less sharpness while keeping roughly the same sweetness. I would not buy anything until that test gives you a direction.

[Probability Paper]

One variable only: extend the bloom by 15 seconds. Why: the last part of the brew may be adding dryness without useful sweetness. Expected result: a 15–30 second faster drawdown and a cleaner finish. I would not buy anything until that test gives you a direction.

[Tofu Asana]

One variable only: increase dose by 0.5 g while keeping water fixed. Why: it changes concentration while leaving the rest of the recipe readable. Expected result: a 15–30 second faster drawdown and a cleaner finish. I would not buy anything until that test gives you a direction.

[Tai Chi Tiffin]

One variable only: extend the bloom by 15 seconds. Why: this coffee may still be releasing enough gas to disturb the early extraction. Expected result: more even early flow and a sweeter cup as it cools. I would not buy anything until that test gives you a direction.

[Fantasy After Midnight]

One variable only: remove the final swirl. Why: the present agitation can be creating fines migration and choking the bed. Expected result: similar total time but less stalling near the end. I would not buy anything until that test gives you a direction.

[Arcade-Afterdark]

maybe check the switch position too, not only the pours. If it was working two brews ago, a small leak or partial open could make the bed behave weird and the finish get sour/bitter at same time… i’ve missed that before 😅

Also the 18 clicks on C3 sound maybe a little fine for this one? i would try 1-2 clicks coarser first, just one cup, and keep the rest same. If the cup gets cleaner fast then it is probably the grind, not the bean.

[Probability Paper]

That is not the relevant comparison. The useful question is not what changed from two brews ago, but whether the filter and brew path are still drying at the same rate. If the drawdown is still 3:20, I would leave the grinder alone for one cup and weigh the spent grounds after brewing; an unusually wet bed or paper clinging to fines would tell you more than another opinion about bitterness. One measured cup is better than three theories.

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