Created by 2016 World Brewers Cup Champion Tetsu Kasuya, the 4:6 method uses coarse grind and timed intervals.
The 40% Flavor Control Phase
The first 40% of the total water is split into two pours. If the first pour is smaller than the second (e.g. 50g bloom followed by 70g second pour), more sweetness and round body are drawn out. If the first pour is larger, bright citric and malic acids dominate.
The 60% Strength Control Phase
The remaining 60% is poured in equal stages (typically three pours of 20% each). Increasing the number of pours increases extraction turbulence and overall strength, while reducing to two pours gives a lighter, tea-like clarity.