Coffee Data Science
Decent Espresso DE1Pro vs Kim Express: Round 1
Kim is the Reigning Champ
I bought a Decent Espresso (DE) in January, and I worked through making the best profile I could. I bought the DE1Pro model. I thought it was time to do a head to head comparison with my beloved Kim Express.
The Kim didn’t just win; the Kim destroyed. This made me question what did I even know about espresso?
We can comeback to that question another day, but today, let’s focus on how different the performance was and some initial thoughts as to why.
The Kim Express is a manual lever produced from the 1960’s to the 1980’s, and then the company went out of business. There are a few still around, but there is no other information about them. The Kim is a spring driven lever machine, and the key difference between the Kim and other lever machines is that the grouphead is inside the closed boiler. Other levers have the grouphead inside the boiler, but the boiler is open.
This design allows for some amazing temperature control between the boiler and the grouphead. The temperature is still not controlled in a control loop, so some temperature surfing is necessary by manually turning off and on the switch. The water temperature can go higher than a pump machine because most pump machines like E61 or DE have a 105C limiter.
My Kim has a slight modification on the pressure relief valve so I can go to 126C. Usually, I pull shots between 116C and 120C.
This is one of the biggest differences compared to the DE. I have tried changing the temperature calibration on the DE to get closer to 120C, but the best I can do is 113C. This is not recommended by the company, and I don’t recommend it either. I used that temperature for these experiments as I was trying to close that gap, but I theorize that some other key difference was missing.
Equipment/Technique
Espresso Machine: Decent Espresso Machine and the Kim Express
Coffee: Home Roasted Coffee, medium (First Crack + 1 Minute)
Shot Preparation: Regular Shots
Pre-infusion: Long, ~25 seconds
Infusion: Pressure Pulsing
Filter Basket: 7g VST over packed to 14g
Other Equipment: Atago TDS Meter, Acaia Pyxis Scale
Metrics of Performance
I use two sets of metrics for evaluating the differences between techniques: Final Score and Coffee Extraction.
Final score is the average of a scorecard of 7 metrics (Sharp, Rich, Syrup, Sweet, Sour, Bitter, and Aftertaste). These scores were subjective, of course, but they were calibrated to my tastes and helped me improve my shots. There is some variation in the scores. My aim was to be consistent for each metric, but some times the granularity was difficult.
Total Dissolved Solids (TDS) is measured using a refractometer, and this number combined with the output weight of the shot and the input weight of the coffee is used to determine the percentage of coffee extracted into the cup, called Extraction Yield (EY).
Intensity Radius (IR) is defined as the radius from the origin on a control chart for TDS vs EY, so IR = sqrt( TDS² + EY²). This metric helps normalize shot performance across output yield or brew ratio.
Paired Shots
I looked at 10 paired shots with similar output ratios across 7 roasts. Aside from one outlier, all the Kim shots tasted better.
The Kim shots tasted better because they had a higher extraction as well as TDS.
When looking at the individual metrics, there were large gaps except for bitter flavors.
I applied a two-tailed t-test, and they showed the differences were statistically significant. This seemed obvious by the data, but a t-test doesn’t hurt. This data set is small but interesting given the large gap.
I did not run this comparison to bash the DE. The DE is an amazing machine, and the profile was made by me after 53 profile iterations and over 100 changes. So there is something fundamentally different between the profile I made and the machine I was trying to emulate. I’ll publish my findings in the coming weeks as I believe I have found an overlooked variable that has not been discussed in the espresso community before.
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