Coffee Data Science
After receiving CoffeeJackI went to work comparing it to other machines, especially the Kompresso, because my goal was to compare it to a standard travel coffee machine. I was pleasantly surprised by how well the CoffeeJack performed. So I want to discuss some of the mechanics of the machine and data from extended employ.
Disclosure: Ashley from CoffeeJack sent me the device because he was interested in my expertise in conducting technical reviews. The people at CoffeeJack will not see this review before it is published, but I have shared my criticisms of the CoffeeJack presented here, as well as my experience. Ashley was very open and willing to discuss design, so I have high hopes for CoffeeJack.
Here’s a video of me doing my typical shot on this machine:
Brief Summary: I like the CoffeeJack enough to replace the Kompresso as my go-to travel coffee maker. Despite some design flaws, its performance outperforms them thanks to its inventive design.
The CoffeeJack is designed to be a portable espresso machine that anyone can employ to make espresso in a variety of settings. I first evaluated the subunits of the machine before collecting further data to look for any flaws.
Pressure:The goal of the CoffeeJack is to be able to produce 9 bars of pressure for espresso or what some consider proper espresso. I don’t employ as high a pressure as the data suggests, lower pressures extract as well or better. So the CoffeeJack was quite effective for me. As a result, I didn’t do any work to test the pressure capabilities and only pressed the mechanical pressure limiter twice.
Temperature: I experimented with boiling water and found that the temperature dropped to 84-88°C after adding it to the chamber. However, even with preheating the machine with steam, the temperature of the water barely rose above 88°C after adding the water. I compensate for this by pre-infusing for a longer time, since I usually employ 100°C or higher in my lever machines.
Shower screen: The water pump goes straight into the shower head, causing the water to flow through the centre of the shower head until pressure builds up in the chamber. This is what bothered me the most and I am surprised there are not more centre channels. I suspect that placing a dispersion strainer between the pump and the shower head would assist.
Filter basket:The first drawback is that the bean logo is right in the middle. This interrupts the flow. But the main advantage of the filter basket is that it has twice as many holes as typical espresso baskets. The same goes for the shower head. I think this design choice allows the CoffeeJack to overcome other issues in terms of performance.
Filter holder: It has a valve, but you can unscrew it. So you could make it pressureless. But it’s not bottomless. That makes some types of bottom-of-screen failure analysis impossible. But they could make a bottomless basket design for people who don’t have to change the machine itself. I’ve worked around that and I think it wouldn’t be a problem for most people.
Coffee machine: CoffeeJack
Coffee grinder: Zero niche & VSSL
Coffee: Home Roasted Coffeemedium (First crack + 1 minute)
Shot preparation: Regular shots and staccato tamped
Preinfusion: long, ~60 seconds
Infusion: low pressure
Other equipment: Atago TDS meter, Acaia Pyxis scale
To assess the differences between techniques, I used several sets of metrics:
Final result is the average of a scorecard of 7 metrics (pointed, opulent, syrupy, sweet, sour, bitter, and aftertaste). These ratings were of course subjective, but they were calibrated to my tastes and helped me refine my shots. There is some variation in the results. My goal was to be consistent across each metric, but sometimes the granularity was challenging.
Total Dissolved Solids (TDS) is measured using a refractometer and this number, combined with the output weight and input weight of the coffee, is used to determine the percentage of coffee in the cup, called Extraction Efficiency (EY).
Intensity Radius (IR) is defined as the radius from the origin on the control chart for TDS vs EY, so IR = sqrt( TDS² + EY²). This metric helps normalize shot efficiency across the entire output efficiency or brewing ratio.
Soil TDS (gTDS) is measured by placing coffee grounds on a refractometer with a little water to measure the amount of solubles left in the coffee. More extraction during espresso leads to a lower gTDS reading.
I started with one shot and took a few core samples. I used them to determine which parts of the coffee were not extracted. In this case, the core was not extracted as well, but that is an outlier compared to the other data.
