Coffee Data Science
Catching the Coffee Sneeze in Espresso
A tissue please?
After a comparison between my Decent Espresso (DE) machine and the Kim Express, where the Kim won handily, I started wondering what about the Kim made the machine so unique. The main parameter is water temperature, but there is something else in the machine design that is giving a clue.
The Kim can operate at 10 C higher water temperature than the DE. The maximum range for the Kim is 123C to 127C, and I have found the range 116C to 120C to be the best for espresso.
At this temperature, the water is instantly vaporizing when one starts the shot until the puck is pressurized. This causes the coffee to be steamed for a split second before water flow starts. This happens because the design of the Kim Express as a lever machine.
As the lever is pushed down (allowing water into the chamber), the chamber above the shower screen is at or below 1 bar of pressure. When the water enters the chamber, it first turns to steam until the chamber is pressurized and shoots the steam into the puck, which I found causes a coffee sneeze.
Once the puck is pressurized, the main advantage to the Kim is a high water temperature. So I wanted to see if I could replicate this effect on the DE by understanding it on the Kim.
How Fast is a Sneeze?
For the DE, I could use above 100C water, and if I used a slow enough flow, it would mostly turn into vapor at the very start of the shot. Then I wanted to determine how quickly this happens for the Kim.
I took some slow motion videos at 240 fps or 1 frame for every 4 ms or so. Based on these videos, the sneeze lasts 12ms or 0.012 seconds.
From these frames, I cut the shower screen so you can better view the water vapor.
Even then, it was hard to see, so I adjusted contrast.
I’m currently experimenting with 0.2 ml/s flow at 10 bars of pressure for 3 seconds at the maximum machine water temperature (105 C). This has been very interesting because this small amount of steam has eliminated the typical side channeling that has caused the donut effect as seen from the bottom of the filter.
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