MANUAL BREWING gives the ability to control every variable in the brewing process, ratio and grind size, degree of agitation and water temperature. This allows the barista to create a cup exactly to one's preference and to the character of the coffee.
There are a few techniques inherent to manual brewing that will alter the outcome of the cup. Bloom, agitation and flow rate.
When hot water comes into contact with coffee grounds; they expand, expelling gases which bubble up. This reaction is similar to that of crema on espresso yet in a much simpler form. Coffee must always be bloomed to allow it to degas. Part of the blooming process is to ensure saturation of coffee, uneven saturation can lead to an uneven extraction of the coffee.
The purpose of agitation is to ensure that the grounds are fully saturated and evenly exposed to water. Under-agitation will result in unsaturated grounds and under extraction, whereas over-agitated coffee can cool the slurry and over extract the coffee.
Agitation occurs two different ways throughout the brew process; manually and as a direct result of the pour.
Using a paddle or stir stick; move the grounds gently back and forth, avoid stirring as this allows air into the slurry, lowering the temperature of the brew.
As the water hits the slurry it churns the grounds, it is important to keep the flow of water moving as to not over-agitate sections of the slurry.
Flow rate refers to the flow of water added to the slurry. Aim to maintain an even flow rate; use the flow of liquid out of the filter as an indication of how much water needs to be added to the slurry. Flow rate plays a vital part of agitation, and maintaining the brew temperature.