In the preceding experiment, Diana Dolejsi and Gwilym Davies made two interesting discoveries: Pouring water into the Clever dripper before adding the coffee grinds creates a considerably faster drawdown, but it also reduces the extraction yield. They identified an opportunity to increase extraction yields of the water-first brews, which trailed those of the coffee-first brews, by grinding finer, without losing much effect on efficiency on the bar. From taste-testing the results of the experiment in Lesson 5.03, they had established a clear preference for the flavour of the water-first brews, finding them considerably less bitter. The goal of their next experiment was to see how much finer they could grind whilst matching the average drawdown times of the coffee-first method.
To begin with, they retested the initial coffee-first approach and again observed a significantly faster drawdown time for the water-first approach. But the next thing they learned surprised us all. They used a popular hand coffee grinder for this experiment which has a grind-adjustment mechanism calibrated as follows:
The Comandante grind adjustment mechanism: Twisting the black dial moves the blades farther apart.
The Comandante grind-adjustment mechanism, The fewer the number of clicks away from the zero setting (where the blades are touching), the finer the grind. The manufacturer recommends 10–15 clicks for espresso, 22–32 clicks for a pour-over filter coffee; and 25–30 clicks for cupping and French press. Image kindly supplied by Comandante Grinder.
Gwilym described his experiences of dialing in for the water-first approach:
‘I was shocked at just how much finer we were able to grind — from 31 clicks on the Comandante to 19. The clicks are pretty much linear, so almost half the grind size.’
Below are the results of their tests. They show a direct correlation between a finer grind and both a higher TDS and a longer drawdown time.