I've had a difficult time with #4 Den's Suimei. I did 4 different tastings at varying parameters, and every time a background bitter brassiness persists. Otherwise, it has a nice lingering palate, which is sweet, and has slight umami seaweed in background after the 2nd steep. The last tasting parameters were less astringent than the first two, 3.5gr/2.5oz/123F/130sec.
3 Tasting Parameters, Sequential
5gr/2.5oz/112F/145sec, bitter brassy
4.5gr/2.5oz/120F/150sec, bitter brassy still
3.5gr/2.5oz/123F/130sec., flavorful but slight background bitterness & brassiness persists, nice lingering flavor otherwise.
120F/90sec; slight astringency/brassiness but tasty sweet, warm, slight green vegetal -- lingering sweet flavors.
130F/90sec., better very slight bitterness still
140F/80sec., thinner liquid, lighter flavor, less brassiness in background, sweeter, nice light lingering palate.
130F/3 minutes; lighter clear green liquid, slightly astringent in background. Lighter but still sweet & tasty. Slight seaweed in background.
140/2min, lighter, not bitter, sweet, thin
155F/2.5 min., liquor lighter again, sweet, slight seaweed umami background.
150F/4 minutes; liquid still very nice green, nice balance, slight sweet to astringent background, warm, not brassy.
155F/ 3 min, very thin sweet flavor.
165F/ 3 min, let it run till I finished 4-5min., very light last steep for sure. Now boil for 15sec.
Bottom Line: a frustrating brew so far; slight brassy bitterness in background, very light thin liquor, although has nice lingering sweet umami. Vibrant green liquor.