Coffee Data Science
Turning a Lever Espresso Machine Full Manual
For the love of levers
I absolutely love my lever machine, the Kim Express. I love all lever machines for espresso, but they are not all equal. The Kim is a cut above. However, I have been doing some tests more recently that suggest a lever design unique in the field levers: Full Manual!
A lever machine typically has a boiler and a lever to push a piston To push water through the coffee puck. There are many designed, but a pressurized boiler seems to work the best. For this design, the boiler has some pressure directly linked to water temperature, and when you open the grouphead with the lever, the water is pushed into the grouphead by the boiler pressure.
This boiler pressure is not manually controlled. I think it could be, and I have been using this idea to great effect recently.
As a result of thermal pre-infusion, I have been able to drop the temperature on my lever to much lower. Typically, I pull shots between 80C and 90C. The challenge is that the boiler is not hot enough to cause significant pressure during the start of the shot or too much pressure.
I had a lot of trouble with this issue during the summer. I bent a shower screen because when I pulled up on the lever to open the chamber above it, no water came out, and the vacuum pressure pulled hard on the screen. Later, I figured out that I could turn the steam wand open which would allow water to come out, but much slower.
However, I did find out something cool. If water comes into the grouphead very slowly, you have full control over moving the water in or out of the puck. You can push the water through the puck, pause, and suck the water back into the chamber. I don’t think this is ideal, but it was interesting considering most machines don’t have a negative pressure concept.
I later realized I could use the steam wand to drop the pressure in the tank. I increased my start temperature to 90C, and when I start the shot, I open the steam wand into a glass bottle which drops the pressure in the tank and slows the water flow almost to a stop.
So let’s design a new machine with two levers:
- One lever for the boiler
- One lever for the grouphead
This would allow me to fully control the pressure of the water going into the grouphead without being dictated by water temperature. This means I could use a lower temperature in my setup. I could also use negative pressure to suck water back up.
Here is a diagram for how the levers would work. The boiler lever, when up would be open, so that the boiler doesn’t have any pressure as it warms up. For this design, no springs are used unlike the Kim Express.
After the grouphead is open, you close the boiler lever to start pre-infusion, which pushes water through the puck. When the filter covers, you can pull back up on the lever to start to pause the flow or cause reverse flow. I’m not sure how that can be best utilized because there isn’t a machine capable of doing that functionality on purpose.
Once one wants to end pre-infusion, they can start pushing down on the grouphead lever.
This design will allow more control. This isn’t always great for workflow in a cafe, but in the world of refining the control we have over coffee processes, this double lever design allows full lever control of the shot.
If you like, follow me on Twitter, YouTube, and Instagram where I post videos of espresso shots on different machines and espresso related stuff. You can also find me on LinkedIn. You can also follow me on Medium and Subscribe.
Further readings of mine:
My Second Book: Advanced Espresso
My First Book: Engineering Better Espresso
