Bluecold wrote:Doesn't this effect invalidate flow profiling as a concept? If you want a given flow, but you have two pressures to reach that flow, it's impossible to reproduce a shot if you only have flow information.
I find flow profiling absolutely essential during preinfusion, when there is no pressure on the puck.
Purely pressure-based espresso machines that describe preinfusion with terms like "3 bar" are giving you some sort of flow rate, dependent on the flow constrictor, and not 3 bar on the puck. The pressure that exists during preinfusion is only that of the flow constrictor on those machines. During preinfusion, the puck is not yet providing backpressure. Only by getting your scale out can you figure out what flow rate those machines are giving you.
I've found that pucks can absorb between 3.5 ml/s to 4.5 ml/s of water. If you go faster than that, you compress the puck before it's fully saturated. This can be a useful technique, for example to create a very thick espresso with a dark roast, but generally I prefer the taste of espressos that have a complete preinfusion (fully saturated puck) before rising in pressure.
The "Pressure profiled shots" on the DE1 are in fact flow profiled during preinfusion, and then switch to Pressure profiling, now that the puck is actually providing pressure. Here is our Default pressure profile, annotated to describe this:
I also use Flow profiling to make pour overs and tea, as well as Allongé espresso, where flow is more important than pressure. Otherwise, I usually use Pressure profiling.
But others are welcome to disagree, which is why Flow profiling is in the DE1 as well.
Bluecold wrote:The graphs and discussion above would lead me to conclude that if you had left the pressure at 6 bar, you would perhaps have slightly less volume, but a much more similar shot.
It's counterintuitive, but it's usually the case that a 6 bar shot will flow faster than an 11 bar shot.