DISCLAIMER: WHAT FOLLOWS IS MY PERSONAL ASSESSMENT AND ANALYSIS. THIS IS NOT SUPPORTED OR AUTHORIZED BY LA MARZOCCO OR LA MARZOCCO USA. MODIFICATIONS SUCH AS THIS MAY VOID YOUR WARRANTY. ADDITIONALLY, IF YOU CHOOSE TO ATTEMPT THIS MODIFICATION, DAMAGE MAY OCCUR TO YOUR MACHINE AND ANY SUCH DAMAGE OR THE RESULTS OF SUCH MODIFICATIONS TO YOUR MACHINE ARE AT YOUR PERIL ALONE. IN OTHER WORDS, DON’T SUE ME, I HAVE ENOUGH SHIT TO DEAL WITH IN MY LIFE. ALSO, CALL YOUR MOTHER AND TELL HER YOU LOVE HER.
There’s no doubt: the La Marzocco Strada EP is a fantastic espresso machine. Aside from the beautiful design (particularly the exposed groups) and standard Strada features, the EP version includes a few extra bells and whistles that justifies the premium price.
The steam wands are regulated by a special solenoid valve, rather than a mechanical valve, which for reasons I’m not 100% clear about, seems to result in a “drier” steam that adds less water weight to the milk. Rather than the paddle-controlled mechanical valve of the standard MP version, the EP features an analog electronic paddle. Each of the groups is driven by an internal gear pump, and you can program in four different pressure profiles. This allows for unprecedented control over the brew water pressure as each shot progresses.
That said, there’s one little thing about the Strada EP that I don’t really love, and I’m thankful that I’ve come across a modification that resolves the issue. Before explaining it, some background is in order.
When talking about coffee-making equipment factors like “brew water temperature” or “brew pressure,” need to know exactly what we’re talking about, and exactly what information the machines and accessories are providing us.
When we have a thermostat in our homes, it’s important to know that the thermostat is measuring the temperature of wherever the thermostat is mounted. Sometimes it’s mounted in a good spot that is a good representation of the temperature that is most relevant to you. Sometimes, it isn’t, and your heating or cooling is a constant source of discomfort and annoyance.
Similarly, “brew water temperature” could be measured in a number of different spots in the machine, with each spot being a different specific temperature at any given moment, with a wide range of temperatures that would surprise many people. The best and most relevant spot to mount a thermocouple (a certain type of digital thermometer) would be right at or above the portafilter basket somewhere. However, that’s a physically difficult place to mount such a thing. So instead, they’ll mount the thermocouple in a more convenient spot, and program in an offset to make up for the typical discrepancy between the point of use (shower screen) and the thermocouple point. That offset can be as much as 10°F (5.5°F) or more.
Pressure is a little easier. If the water pressure is at 123 psi (8.5 bar) in one part of the open system, it’s going to be 123 psi in a different spot in the same system. Bends and tubes and narrowing and such can change that a bit, but in general, pressure is distributed evenly. For an espresso machine, this is pretty much true everywhere in a brew group between the pump and the coffee in the portafilter. But what about that coffee in the portafilter?
In that coffee “puck,” there’s a pressure gradient. Below the portafilter basket, (at sea level) the pressure is 1 bar (14.5 psi), since it’s in “normal” atmospheric pressure at that point. Above the coffee puck, let’s say it’s 8.5 bar. Within the puck, there’s a gradient that transitions from the 8.5 bar to 1 bar. It’s not evenly distributed downward through the puck, instead the majority of the transition happens mostly at the very bottom of the puck. But that’s all with coffee in a portafilter.
If you had, instead, a blind filter (basket with no holes) in the portafilter, and you turned on the group, the resulting pressure would be a little higher than 8.5 bar. Because there’s no pressure drop out of the portafilter, your net pressure would be higher. Not a LOT higher, because of the way the pumps work.
On the Strada EP, rather than a vane pump like every other La Marzocco on the market, each group has a gear pump, and a pressure transducer (pressure measurement sensor). When you program in a pressure profile, the software takes the data from the pressure sensor, and saves it into memory. When you playback a pressure profile, the software works to replicate that same pressure sensor data by controlling the pump, which in turn it controls by adjusting the voltage sent to that pump. That makes a lot of sense, doesn’t it?
There’s a different way that the machine could work. Instead of having the software replicate the same pressure data, it could just replicate the pump voltage.
Let’s go back to the normal EP setting, where it works to replicate the pressure data. You dial in the pressure with a particular coffee, roasted a particular way, ground on a particular grind setting, a particular dose (amount of coffee grounds), and a specific lateral distribution. As you replicate that pressure profile throughout the work day, you’ve very often changed one or more of those coffee variables.
If you change only one variable: use less coffee, the pump will have to work harder to create a little more pressure to make up for the slightly lower resistance from the coffee. If you grind finer, then the pump will generate slightly less pressure, since the coffee has a higher amount of resistance to the water flow.
So what happens if your distribution develops the fearsome “channeling?” If, with all other things being equal, there’s an area of the puck that results in a “channel,” or a path of less resistance through which more water flows through than the other parts of the coffee puck, what would happen? Well, on an average espresso machine, the pump being “dumb” and not directly responsive to changing conditions, there will be a bit of overextraction of that part of the coffee mass, and a corresponding underextraction throughout the other areas. But the Strada EP is not an average espresso machine.
So what does the EP do when it encounters a channel? The pump will generate more pressure to make up for the pressure loss, effectively making the channel worse.
All of this background is to set this up: there’s a modification that changes this. MORE DETAIL HERE
If you change these control board jumper settings (you need one extra jumper), it effectively defeats the transducer-pump feedback loop and the pressure profile that you program in controls the voltage of the gear pump only.
To be clear: because the gear pump does not work to reproduce a specific pressure anymore, differences in your coffee puck will result in different numbers on the pressure LCD display. However, you might choose to relax a bit, since that’s the way pretty much every other espresso machine actually works. The group pressure transducer gives us a bit of information that we’d otherwise never have access to, so we really have to manage our expectations about how that information is going to look.
At our Wrecking Ball Coffee bar in San Francisco, we’ve been running our 2-group Strada EP this way for almost two months now, and the machine is much more user-friendly. We still have unprecedented pressure profiling, but without the additional element of the feedback dynamic. When there’s channeling, it’s a typical channeling. When we make coffee-related adjustments, the “peak” pressure on the display is often different than before. But, most importantly, the coffee is more consistently delicious.
If you’ve read this far, you’re a freaking nerd and you need to get a life, dude.
Despite the disclaimer that this post started with, thanks to Scott Guglielmino from La Marzocco USA for providing me with the jumper settings. If you choose to do this mod, and you like what the results are, and you’d like to show any appreciation, please do so with a small donation to Food for Farmers. Also, I’d love to hear your results.