Darcy’s law describes the decrease in flow rate as the coffee bed depths increase,
For this reason, we tend to grind coarser for larger brew volumes.
E.E. Lockhart (the architect of the Coffee Brewing Control Chart) recommends using a coffee depth of between 1–2 inches (≈ 2.5 and 5 centimetres)
There is a lot of potential to lose heat from the air-water interface at the top of the slurry. Evaporative cooling is accelerated by moving air so we recommend you avoid placing ventilators directly above your brewbar.
Air velocity of up to 3 meters (about 10 feet) per second can double the rate of evaporative cooling.