Mypressi Twist - Technical

[kkyoon]

Blind Test Extraction Measurements

Tests were done with a Mojo Refractometer. Coffee dose was measured using a 0.1gm scale before tamping. Espresso was pulled into a cup sitting on the scale and the cup was pulled when the shot approached the target beverage weight. Measure results show that extraction is in the ideal 18% range and is very consistent across both devices and from shot to shot. Both the "steam" and "soak" preheat performed identically in this test.



Brew Temperature Measurement / Preheating

The brew temperature was measured with a quick responding 30 gauge fine wire thermocouple, inserted over a plastic block machined to fill up almost the whole filter basket. This ensures all water flows down the hole in the middle past the thermocouple. A fine hole was drilled in the bottom of the block to simulate the correct water flow rate of espresso extraction. This resulted in the emptying of the water chamber ( filled to the top, around 80ml ) in 25 seconds - see sudden drop in temperature graphs . A calibrated thermometer was used and connected to data acquisition software on a PC via RS232.





To ensure correct brewing temperature of 90-94 degrees, it is necessary to preheat the water chamber. Three preheating methods were tested:

Steaming ( top of Mypresso handle and water chamber put in kettle above water level, 2mins above boiling water)




Soaking ( filling water chamber with boiling water and soaking for 20 seconds, then repeating once, then fill and pull )




Steam wand preheat ( filling hot water in water chamber and heating it with another espresso machine steam wand ).




All three resulted in consistent and acceptable brew temperatures. Brew temperature hardly dropped during the pull - very good temperature stability. Extraction measurements and taste confirm correct brew temperature compared to a commercial machine.




My theory about the consistency of brew temperature is that we are starting from a know reference temperature, which is 100 degree rolling boiling water. If you preheat the device for the same amount of time every time, each pull will be very close in temperature. As for stability, I believe that the water chamber temperature will reach equilibrium with the filled boiling water quickly, after which the temperature of the whole device will only drop slowly. As it is a gas which is pushing the water down, there will be minimal drop in temperature ( compare with room temperature pumped into the boiler of entry level single boiler machines! ). You can experiment with lower temperatures by varying the wait time before pulling - open you find the sweet spot for a specific coffee just repeat the same wait time and you will get the same results.

[kfchan]

Excellent review guys.

I think the only reasonable pre-heating method is via soaking. The other 2 methods of steaming and soaking are way too much hassle.

Your experiment shows that the Mypressi Twist is a formidable espresso making product in a controlled environment. In any home brewing (aeropress, syphon etc), the small electrical kettle that give fast boiling water on demand is an absolute necessity. Count down from a rolling boiled water is the best way to control temperature. Even without a thermometer, it is still reasonably accurate and reliable.

What happened when you are not at home? Based on the "ease of use" mantra...
Using water from the following:-
1. Using those thermos water heater (not sure if that was the description) that supposedly can maintained temperature at 98 celcius.
2. Thermos flask

What level of acceptability would the espresso be?
Compare to your review of 4.5, I would say if using uncontrolled temperature devises as above and can reach 3.0 on espresso quality, then it would really be a worthwhile investment.

[CuppaMun]

Great work!  There was a referral to your temperature chart from the maker of mypressi TWIST!  Check out the short comment at www.facebook.com/mypressiTWISTMalaysia.