Pressure Profiling on the Decent Espresso Machine
I've had a DE1+ at my house for the past few weeks and I've already learned a ton. In this post, I'd like to introduce readers to the "pressure" and "flow" modes of the Decent. In the next installment we'll discuss the "Advanced" mode and I'll introduce some new ideas about espresso extraction that I've learned from the machine.
The DE1+ comes with a tablet computer and quite a few sensors. There are so many sensors that the sensors are literally monitoring each other to ensure they are as precise as possible. Instead of a boiler the DE1+ has a "thermocoil", or continuous water heater (the De1+'s temperature profiling would be impossible with a traditional boiler), the machine measures temperature just above the shower screen (not at the boiler, a major improvement), and it mixes hot and cold water continually to maintain precise water temperature at the screen. The steam runs extra hot in order to squeeze the most juice possible out of standard home electricity. On the tablet you can program the hot water tap to dispense water at any chosen volume and temperature. Within five minutes of turning it on in the morning, the machine is ready to make coffee at a precise temperature -- no sink shots required. When using a bluetooth scale, the DE1+ can stop shots gravimetrically.
Any one of those features would probably cause the professional coffee community to get excited about the machine. But none of those innovations are what makes the Decent the best espresso machine in the world. What's amazing is that it can brew espresso using pressure profiling, flow profiling, or a combination, and the barista can see the pressure, flow, and temperature curves in real time during a shot. The feedback provided by those curves is invaluable. It's like Cropster for espresso, and once you see it, you'll never want to pull a shot without it. After pulling hundreds of thousands of shots over more than two decades and learning quite a bit along the way, I've probably learned more about espresso extraction in the past few weeks than I had learned in the past ten years.
The pressure mode is somewhat like that of other machines that offer pressure profiling, but the DE1+ allows the barista to see the results of his or her efforts and adjust accordingly. Given that we can taste only so many espressos per day, one can progress only so quickly by pulling shots, tasting, adjusting, and repeating. With the Decent, it's obvious which shots are worth tasting, which need a finer or coarser grind, and how much each shot channeled. That means I can dial in a shot nearly perfectly before bothering to taste it. My palate is grateful for the assist.
Programming in pressure mode is simple and Intuitive. You can program preinfusion to end based on a particular time or pressure target. Contrary to popular belief and what other machines' pressure gauges indicate, one does not preinfuse at a particular pressure. This is because no matter how hard the pump works, the puck must provide back pressure before the system is pressurized. Preinfusion works at atmospheric pressure until the headspace above the grounds is full of water, then pressure ramps up as the grounds absorb water, swell, and provide increasing amounts of back pressure.
In the example below, I have asked the machine to preinfuse at a flow rate of 4 ml/s until 15 seconds has elapsed or the pressure reaches 6 bar. As soon as one of those goals is met, the machine moves on to the "rise and hold" phase, in which I've asked it to rise to 8.2 bar and hold that pressure for 10 seconds. Next the machine will lower down the pressure to 5 bar over 30 seconds.
Below is the resulting shot.
The green line is the pressure curve and the blue line is the flow curve. The curves offer a treasure trove of insights:
The volatility in the green curve indicates channeling (note the channel near the top/right of the red circle.) The volatility of the pressure curves on the DE1+ come from two main sources, as far as I can tell: clumped grounds and poor puck prep. In this case, I'm using a grinder that is producing an incredible amount of clumps. The grinder hasn't been aligned or fully seasoned and I'm hoping that I can improve the grind quality soon and the volatility will decrease. Bigger, better, sharper burrs generally produce smoother curves-- that's obvious when I pull shots from two different grinders. As a side note, one remarkable thing about the Decent is that in flow mode it "fixes" channels. More on that in the next post.
The blue curve shows that the flow rate dipped after preinfusion and took a long time to level off. This is what John refers to as a "slow-to-develop shot." We think this happens due a combination of possible reasons: the grind is too fine, the puck is too compressed (more on this in a later post), or the puck is still absorbing water during the 15--20 seconds after preinfusion ended because preinfusion didn't fully saturate the puck. We have generally preferred espressos that didn't have such a dip in flow rate, and we're still working on the significance of this. Speculations are welcome. (For the record, we have preferred shots where the flow is steady almost immediately after preinfusion.)