I start the day with mediocre coffee. Yes it’s now 9 bar blabla; I still don’t love it. I’m thinking. I’ve created the profile I’m using to recreate what the unmodded machine was doing, at a different pressure level. It comes as no surprise that the result doesn’t change much.

There is a collection of community profiles for the Gaggiuino mod. I read through the descriptions and pick the LMD 9-8 v1.5 profile, mostly because it’s the only one that mentions “darker roasts”.

Designed for medium to medium-dark beans, the goal is to optimize for even extraction while minimizing the overextraction that can be common with darker beans. This is done by transitioning from a pressure target to a flow target during extraction.

I don’t understand any of the nonsense about flow targets, but the overall description sounds good. Let’s give it a shot (no pun intended). I don’t even know how to properly import profiles, so I just manually program them into the machine reading the JSON file.

The profile has a pre-infusion phase. Premium stuff. After 6s it starts the extraction. The coffee comes out thick and syrupy. I taste it. Damn that’s good. Easily the best shot I’ve ever pulled. And I haven’t even started dialing it in.

I get excited. I change the grind setting one whole tick finer (one tick is a lot on my grinder), because I feel like the shot is a bit sour. Second pull. It flows even nicer. I taste it. Crazy. This is it. I made it. That’s so close to the one shot in Vienna that started all of this. My girlfriend confirms the victory. What a day.

WTF just happened?

Let’s get to the bottom of this. I think I need to explain how the LMD profile works. Profiles in general are separated into phases. The machine uses stop conditions to decide when to transition from one phase to next one. Finally, you can set a global stop condition that will end the shot (like 36g of coffee created, or 25s of overall shot time, etc.).

Each phase has a target. The target can be either pressure or pump flow (the amount of water being pushed by the pump per second). You can make the target a function from x to y, or you can set a fixed value.

The LMD profile starts with a pre-infusion phase. It fills the puck with water and then waits 6s for it to soak. Then, it ramps up the pressure from 2 to 9 bars in 4-5 seconds, only stopping if there’s too much flow. From there, it reduces the pressure to 8 bar during 4s. Finally, it holds a steady flow rate until the shot is done. In other words, it does a pre-infusion, ramps up the pressure and then tries to maintain an even flow rate.

Pre-infusion

Pre-infusion means soaking the coffee before starting the real extraction with high pressure. It has two big effects.

1. It helps the extraction, because the solubles in the coffee start to dissolve during pre-infusion. This makes it easier to extract them in the high pressure phase.
2. It helps against channeling. Channeling happens when the puck is not evenly dense, i.e. when it has “holes”. During the soaking, the puck expands which evens out the density and closes the holes.

Other machines achieve this using a neat mechanical trick. They have a flow restriction device built-in. This is basically a part of the tube between the group head and the boiler that’s way thinner than the rest. When the system gets pressurized, the flow of water into the grouphead is restricted. This makes for a gradual increase of pressure until the system pressure is reached. It’s debatable if this counts as pre-infusion or if it is part of the pressure profile of the machine though.

Steady flow

After the initial pressure ramp, the profile keeps the pump flow steady. This results in a slight pressure drop, but keeps the espresso flowing very evenly. In my opinion this helps against channeling too, because a fixed pressure works against the puck, while a pump flow target lets the puck lose it’s resistance without forcing more and more water onto it.

Conclusion

So all in all I think that the LMD profile does one thing essentially: It avoids channeling. Every phase contributes to this goal. The taste of my previous shots were thus dominated by channeling effects. This explains why I had such a hard time determining what exactly was wrong in the coffee. The taste was so muddy compared to the new one.

There’s some more reading about pressure profiling. I’ve found this resource that talks in very technical terms about the subject. Also, there’s this wonderful video of James Hoffmann that explains the basics very well.