Remilar — pour-over coffee brewing | remilar.com
Why 96 C is the documented ceiling, what boiling releases, and how grind size changes the flow through the cake.
Two temperatures govern the cup. Aromatic oils in coffee are released at 96 C (205 F), just below boiling, while bitter acids are released when the water has reached boiling point. The gap between those two points is the whole temperature strategy of this method: hold at 96 C and the oils come out; let the water boil and the bitter acids come with them.
The grind sets the bed that the water crosses. A finer grind packs the cake tighter and slows the seep through the paper filter; a coarser grind opens the bed and lets the water pass faster. Either way the water must cross the whole cake before it reaches the filter, and an uneven bed leaves part of the grounds under-crossed.
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The chamber works with the grind: the conical, trapezoid or cylindrical form shapes the flow, and the flow decides how long the water sits against each part of the cake. A conical chamber concentrates the flow at the center point; a trapezoid spreads it across a flat bottom; a cylinder keeps it even along the full height.
Together, temperature, grind and chamber shape determine whether the cup lands on the oil side of the line or the bitter-acid side. The parameter table on the main page ties each of these to its step in the procedure.
Further reading