I started using my Lelit Mara X back in April and thought maybe I would try my hand at flow profiling so I bought Lelit's flow control system. Not sure if it matters or not, but I also just switched to an IMS Precision Shower Screen and a VST Precision Filter Basket.
Up until this morning, I noticed the shots I've been pulling with the dark roast have been pretty bitter. So I read on here about adjusting to a coarser grind.
With the smaller grind, I noticed both the pump pressure and group head pressure were both around 9-10 bar and the shot had a decent amount of crema.
When I switched to a coarser grind, I noticed less bitterness in the shot but the pressure at the group head was only at 2 bar (pump pressure was still at 9-10 bar) and there was barely any crema.
Is the lack of pressure at the group head and lack or crema normal / directly related to the coarser grind setting?

Thanks!
Chris

Maximus146 wrote: Is the lack of pressure at the group head and lack or crema normal / directly related to the coarser grind setting?

Yes.
You'll want to find a grind somewhere in between the "fine enough to make it bitter" and so coarse the water basically falls through without creating more than 2 bar pressure... Once you have a grind and dose that repeatedly gives a pressure of about 8 - 8.25 bar on the gauge you can try throttling your flow with the flow control to get most of the shot flowing at just under 8 or 8. and see what you think of that. (This is the most basic of answers)

Because you have the flow control on your machine, you could try keeping it coarse where it is, but giving it a very long pre-infusion with the flow almost completely cut off. When the grounds are thoroughly wetted and have expanded as much as they're going to, slowly ramp up the flow so as not to disturb the puck, all of the resistance to flow will be from the puck and you will produce the crema you're looking for.

Ok so two different options to try out.

As far as the second option goes, how long of a pre-infusion do you think it would take for the puck to be wetted enough before I slowly ramp up the flow?

Thanks again,
Chris

"Bitter" is often a sign of extracting more from a coffee than one's taste might enjoy. Grinding coarser is one approach to reducing this kind of bitterness. Another is to cut the shot short of blonding, often with a shorter ratio (below the typical 1:2, even as low as 1:1).

Increasing soak time with flow control is often done to increase extraction. In my experience, extended soak time makes a "comfort" espresso unacceptably bitter. What it would do to a dark roast could be even more starkly bitter.

If you're not familiar with the basics of adjusting by taste, Espresso 101: How to Adjust Dose and Grind Setting by Taste is a good introduction.

At least from my experience, the only thing I'd do with flow control and a dark roast would be a lever-like declining pressure during extraction.

Ok I still have to re-adjust my grind size so the water isn't just running through the puck producing no pressure at the group head and no crema correct?

Grind/dose should be enough to generate 4-6 bar of pressure or, for a more classic profile, 8 bar. Below around 4 bar you can get a tasty drink but, for many people, it isn't "espresso" but something starting to have more of a filter coffee flavor profile.

Crema is a byproduct of extraction. It's similar to beer foam. The amount and texture of crema is not an indicator of how well the espresso was extracted in terms of taste.

I don't pull much darker roast, minus stuff like Chromatic Opus which is leagues beyond what almost any roaster does for dark roast. But even med dark, I'll pull normally at 8.5 bar where I have opv set anyway but if profiling I'll start dropping it at points like to 7 bar, than 5 bar etc to finish. Chromatic is delicious period, but I've had even medium roast that had bitterness I couldn't shake and profiling down like that makes quite a difference.

Opus though is king for me for dark roast, it's amazing straight, milk, normal ratios or ristretto. But I've had other beans where I've had to play profiling.

Maximus146 wrote: As far as the second option goes, how long of a pre-infusion do you think it would take for the puck to be wetted enough before I slowly ramp up the flow?

To be honest, I don't have a clue how long in terms of seconds. I'd try times that would kind of reproduce how long it takes a plumbed in machine to pre-infuse and drip the first drop, so like 7+ seconds. I'd try longer to see how it mattered, because knowing the coffee puck isn't the actual restriction with the flow control, surely 7 seconds wouldn't be enough. My experience with flow controls is very little. I don't own one. I have had very simple training on how to use them. I play with them on customers' machines because I want to get to know them.

Jeff wrote: Increasing soak time with flow control is often done to increase extraction. In my experience, extended soak time makes a "comfort" espresso unacceptably bitter. What it would do to a dark roast could be even more starkly bitter.

What he said.

Flow control is primarily useful for light roasts that are difficult to extract. It allows you to grind much, much finer and increases contact time. That's not what you want with a dark roast. Dark roasts extract easily, so if you use long, slow preinfusion, the coffee will be over-extracted and bitter.

For the best tasting shot from a dark roast, grind coarser, increase the dose and/or pull shorter (Ristretto). This reduces surface area of the grinds and contact time. You can also try reducing the temperature.

Never thought about reducing temp....I'll give that a shot also