Questions Answerable by (or with) a Coffee Roaster

Going to over-reach a bit and describe an espresso roasted single-origin - and guess about why it is the way it is. Feel free to comment if anything rings a bell.
  1. Moisture content: unmeasured; bean appears to be on the drier side, as clumping is minimal and grinds fly out of the chute like loose sand.
  2. Hardness: unmeasured; bean appears to be of moderate hardness, as it hardly channels with medium-pressure tamping and a moderate (4-5s) preinfusion.

    (Supporting 1) and 2), the bean crunches easily if you chew it.)
  3. Baking: no apparent baking in the roast, as there is an absence of grainy / malty flavours, and very little astringency of any sort however...
  4. Scorching: no apparent scorching as there's very little bitter stuff to complain about.

Now, I am wondering the following phenomena:

  • while the overall flavour profile is floral and pleasant at low-temperature extractions (90.5C) , extraction yield appears to be low: lower than in other recent roasts of the same origin (evident from taste, and crema yield);
  • if we pump up extraction temperature to 92C, we get a rapid increase in sour, umami, and browned flavours, but not a whole lot more crema - it is near impossible to serve this temperature's brew as a black coffee, to anyone who dislikes the slightest acidity in their coffee (see (4 above) - we'd normally pull a 23s ristretto, but even at 40s lungo, acidity remains unmasked by whatever else can be extracted from the bean;
Anyway, I have zero experience with roasting coffee, and was just wondering if this could be due to some sort of roast under-development between first and second crack.

In light/medium roasting, is it possible that you can achieve a favourable flavour profile, at the cost of reducing the quantity of extractable flavonoids and oils in the bean?


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