CHAMBERED GROUND COFFEE

Hello Faithful Reader,

If your reading my blog your probably pretty well dialed in on making artisan espresso. You have fresh coffee, sharp grinder burrs, clean PID machine with proper settings on temperature, pre-infusion, and brewing pressure. You have clean, filtered water and perfect barista technique. So you are able to make pillowy ristretto shots that quote the fragrance in their aroma and flavor. But you can only conjure the goddess when flow-rate is perfect.

I have stated several times that ground coffee, trapped inside the grinder, makes it impossible to control the flow rate of the espresso. This is a key concept so let’s break it down.

After roasting the coffee bean still retains some moisture inside of it, like a memory from when it was fresh and green and wild….The more moisture remaining after roasting the more coarse the grind setting will be to achieve the perfect 28 second, oozing pour to achieve about 20ml of crema. For example the grind setting for my Brazilian Porta Rosa is quite coarse to hit the pour, meaning it has higher internal moisture. And if I prepared Monsooned Malabar, with the same grind it would be a 15 second extraction and be very sour/astringent. (It seems counter-intuitive that soaking the green beans in water for ten days would result in a bean that is drier inside. But as always I just follow the coffee and report the trip).
Another property of ground coffee is it is very hygroscopic, exchanging moisture very quickly with the ambient atmosphere. That is why as a barista in a shop you need to change the grind as the store experiences changes in the humidity to maintain your flow-rate.
Inside most of the grinders available today the ground coffee exits the burrs into a circular steel chamber, a little moat around the burr set. Inside the steel moat are paddles spinning around to push the grounds into a chute of some kind to travel to the porta filter. As soon as you shut off the grinder the paddles stop and the moat contains at least 10g of ground coffee, and the chamber another 10g.
This trapped coffee immediately begins to lose moisture. This desiccation process is heavily affected by the ambient atmosphere, the heat within the grinder, and the residence time in the grinder. In short, it is impossible for the barista to control the flow rate. The pour will be faster but never in a consistent, predictable way.
The flavor profile that survives extraction into the cup is fantastically volatile, wildly different with very subtle changes in the speed of the flow. We like a leisurely pour that oozes into the cup between 27 and 31 seconds to become 20ml of silky crema. Within those time limits are dozens of distinct flavor experiences, as different beans in our blend come forward. Maybe a 28 second extraction is heavy on the chocolate/umami and blueberry from the Ethiopian. A 30 second extraction may feature more salted caramel from the Malabar. None of these pours are defective, just unique.
The barista is a magician conjuring the seductive aroma into an ephemeral foam that is itself ever changing within the cup. I’m not bored yet….the more I learn the less I know.