Blue Bottle Coffee · Night Light Decaf

Clean flow, hit the ristretto target, decent numbers — but balance came in at 2 (sour) with lingering acidity that only partially resolved with milk. This is now the third consecutive shot at grind 36.5 or finer producing sour linger, and the fifth sub-40.5 shot showing the same pattern. The evidence is unambiguous.

Time was 23s (Fast) and ratio 1.53 (Ristretto) — both fitting a ristretto pull, target hit. Flow notes were clean: even start at 10 seconds, no channeling signals. The sour linger is not a flow or technique problem. At grind 36.5, this bean is consistently under-extracting despite clean mechanics — finer grinds are definitively not the path forward on Night Light Decaf bag 21.

Night Light Decaf's Swiss Water process opens the bean structure, which means it extracts more efficiently than a regular medium roast — coarser grinds extract well where finer grinds over-restrict and under-extract unevenly. At 25 days off roast it's in its freshness window. Bean character includes key lime in the notes, so a hint of brightness is expected — but lingering sourness that survives milk is extraction, not bean profile. Grind 40.5 resolved this cleanly before.

Three shots in a row probing finer grinds have all confirmed the same result. That's good diagnostic discipline — the bracket is now closed. Time to commit to the coarser baseline and dial in yield precision from there.