Coffee Data Science
9 Bars of Pressure, Really?
A nearly impossible and unnecessary feat of strength
For years, I have been using the Cafflano Kompresso for portable espresso. Based on my routine, I have not found a case where I hit anywhere near the maximum pressure possible, but I have been curious. They have claimed you can pull a 9 bar pressure shot with their device, and I have previously looked at using a scale to see what pressure I could get the device up to. I failed to hit 9 bars, but I decided to give it another shot using a digital pressure gauge to tell me what’s going on inside.
For this experiment, I modified a Kompresso basket to include a Pressensor to measure the pressure build up inside the basket.
The first shot I pulled ended up at a very low pressure, and this is similar to the type of shot I would normally pull.
So I ground much finer. I went from a 200 um burr gap on the Zerno to 100 um. 200 um is the typical burr gap I use for pulling shots on the Decent Espresso machine. This caused a lot of channelling as one can see by the dark spots in the spent puck.
For this attempt, I had the device on the counter, and I tried multiple times to get to 9 bars of pressure, but I failed.
So I tried again, but this time I put the Kompresso on the floor where I could use my full body weight. After the first push failed to hit 9 bars by a smidge, I had to add more water. Afterwards, I was able to get over 9 bars.
However, the amount of effort was very large. As you can see from the photos, the black plastic part was bending when I hit 9 bars of pressure, which is not safe.
The device can hit 9 bars as advertised, but I would never go over 4 or 5 bars simply because the user experience isn’t great. Also, between thermal pre-infusion and blooming, it doesn’t need high pressures to make good espresso using Kompresso. Usually 2 bars or lower works just fine.
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Further readings of mine:
My Second Book: Advanced Espresso
My First Book: Engineering Better Espresso
