In a previous post on the gravimetric espresso project, I gave a sneakpeek of the pressure controller (AC voltage controller) which is hooked up to the Ulka vibration pump. The AC voltage controller is commonly sold as ‘AC 0-220V 20A Pulse Width Modulator PWM Electric Motor Speed Controller’, and I’m going to demonstrate what is possible with this low-cost hack!

Disclaimer: I am not liable for any damage, death or injury caused through the use of this hack.

This video demonstrates the effect of flow-rate as the voltage control knob gets adjusted. The flow-rate went from ~3 ml/s to ~4ml/s to ~5ml/s.

Why control the flow-rate?

Flow-rate control allows soft-infusion of coffee ground, and soft-infusion of the coffee ground prevents migration of ‘fines’, these are usually the smallest of the coffee ground which clogs up the tiny holes at bottom of the basket.

Lesser migration of fines = Lesser chances of espresso getting choked

This also means that ground made with finer grind settings can be extracted without choking the machine.