First, I tried compensating with more coffee. That just made the cup stronger but still sour. Then I tried a finer grind—that helped a bit but introduced bitterness. The real breakthrough came when I started measuring water temperature at the slurry, not just in the kettle. In a cold room, water can drop 10°F between the kettle and the brewer. That alone is enough to under-extract.

Another attempt was to preheat the ceramic dripper with hot water while the kettle was coming up to temp. That helped hold heat, but only if I did it right before brewing. Letting it sit for even a minute negated the effect. I also tested wrapping the brewer in a cloth napkin during the bloom—awkward but effective.