Historically, there has been a lot of discussion in the coffee community suggesting that a straight, flat flow profile is best in all cases. However, that does not seem to be true in practice. Completely taming the acidity by straightening out the line can make the coffee taste flat and boring, much like a wine that lacks acidity. Allowing the flow rate to dynamically change rather than forcing it flat preserves the essential acidity that keeps a cup interesting.
If you dial in a starting flow rate as slow as 0.5 ml/s and allow it to increase to around 1.2 or 1.5 ml/s, you are pulling what is considered an "ultra-thick" shot. This style is characterized by extended water contact time, high total dissolved solids (TDS), massive body, and a texture reminiscent of chocolate syrup or mayonnaise. A typical lever machine operator wouldn't let the shot speed up; they would purposefully jam the puck with an immediate surge of water and then back off the pressure to keep the stream thick and gloopy.
For these ultra-thick styles, it is best to configure a more severe pressure decline over a longer extraction window, sometimes lasting up to 50 seconds, to ensure you get a sufficient volume of liquid in the cup. Slide the end pressure setting on the default profile down from the standard 6 bar down to 3 bar, or even all the way down to 0 bar. Ending at zero pressure mimics traditional lever machines where the mechanical spring completely gives up at the end of the pull, allowing you to simply pull your cup away once you hit your target yield.
If you want to move away from heavy, chocolate-bomb profiles and want the subtle flavors of your dark beans to open up, you can try two different methods:
For baristas who naturally prefer a balanced, chocolate-heavy profile but want to start exploring medium-to-light roasted coffees, blending is a highly effective stepping stone. You can pick up a small bag of natural-process coffee beans featuring fruit notes that complement chocolate (such as strawberry, passion fruit, or tropical flavors). When weighing out a standard dose, replace just 2 grams of your usual chocolatey beans with the natural-process light roast to complexify the cup without overwhelming it with acidity.