My typical process of dialing in a bean goes something like this:
1. Adjust grind to achieve a 1:2 (dose : yield) ratio in ~30 sec.
2. Pull another shot, stopping short for a 1:1.5 ratio.
3. Pull another shot, stopping long for a 1:2.5 ratio.
4. Taste each of the three shots, and pick the ratio I prefer based on taste.
5. Keep selected ratio constant, adjust grind (finer or coarser) to get desired taste.
The above process assumes a static preinfusion pressure.
Where does the digital preinfusion capability of the LR fit? Do I arbitrarily pick a preinfusion pressure to start with? If so, what pressure? Do I adjust preinfusion pressure after step 5?
How do I know if my preinfusion pressure is too high? Too low?
I appreciate the help as I'm new to the LR. Previous experience has been E61 machines where my I had no ability to control preinfusion pressure.
i tend to take a simpler approach, using the machine to make life easy as i have designed it that way
a dark roast likes a shorter shot, as they extract more readily, and the opposite for a light roast
my machines take care of this for you as a change in pre-infusion pressure moves all the parameters in the correct direction
so use a constant dose to get started, typically 18g in our 18-20g IMS basket, and just vary the pre-infusion pressure
the LR comes set to 3 bar at the puck out of the box (ensure the offset is -1.0 bar not -1.4), and this isnt a bad place to start
if you have a dark roast you are going to be dialling the pre-infusion right back to boiler pressures that we had on the L1(2012-16), eg 1.3 bar and the lever will grab much higher and the shot will be much short to prevent over extraction and it all works in harmony to get you an optimal extraction
you might even drop down to 1.0 bar pre-infusion
i would define a dark roast as one having oil on the surface of the bean - bear in mind that a relatively dark roast will not have much more than pin pricks of oil on the surface of the bean when first roasted; the oil comes to the surface with the passing of time
the lighter the roast the more pre infusion pressure you give it
this automatically gives you a higher brew temperature at all points on the curve, brings much needed body to light roasts, and increases the shot volume (i.e. it automatically extends the brew ratio for you - you dont have to worry about any of that fluffing around)
does it taste burnt or sour (a slightly queasy taste), or sweet?
if it is sweet you are bang on; dont change anything
more likely you will be under or over on the first shot though, so if it is sour go up 1 bar and try again using the same dose, grind, tamp, etc
if it has burnt notes then drop 1 bar and try again
if a movement of 1 bar takes you too far, ie. a sour roast now exhibits burnt notes or vice verse, split the difference, i.e. drop back 0.5 bar back towards the pressure value that you started with
keep splitting the difference in this way until you get it just the way you like it
be aware that the taste of a coffee shifts as it ages, with the CO2 gassing off in particular in the early days post roast really moving the taste around, so you can expect to have to tweak the pre-infusion pressure every day if you insist on drinking coffee that is too fresh
Thank you very much for your helpful reply. I discovered that my machine's offset was -1.7, so I reset it to -1.0 as you directed.
I'm using a med-light roast (Goshen Coffee's Bona Fide espresso blend) and kept a constant dose, and started with a 3.5 bar preinfusion pressure. I then brewed shots at various pressures, and here's what I found:
2.5 bar = more sour
3.5 bar = sour
4.5 bar = less sour
5.5 bar = sweet; slight hint of sourness
I ran into some pump-related issues at 4.5 bar and higher, which I posted about under the LR help forum, so I wasn't able to establish a relationship between preinfusion pressure and preinfusion time.
I'm still undecided about where to insert preinfusion adjustment into my dialing in process (before or after determining brew ratio), so I've got more experimenting to do.
just getting my daughter off to school and will reply to both your posts more fully in a couple of hours, but your data above suggests to me that your coffee remains 'sour' or 'slightly sour' at such high pre-infusion pressures because either your puck prep has scope for improvement, or you have some silicone grease in your shower screen, or both; but i am almost certain you have some channelling going on and for this reason the shot will remain sour regardless of the pre-infusion setting
can you post a short clip of an extraction and another with the portafilter removed from the group and a short flush of the group so i can observe the water fall pattern through the shower screen for any signs of jetting