Optimum flow rate w/o portafilter (water debit)

(Alexander Buzath) #21

… maybe it’s just a matter of avoiding extremes?

extreme 1: too much fast flowing water hitting the puck very hard

extreme 2: water needs too long to reach the lower regions of the puck

(Troy) #22

Is it?

I would argue that with respect to espresso extraction, “evenness” is somewhat of a fallacy anyway. The temperature, concentration and even density (and thus velocity) of the fluid will likely all vary spatially through the puck. Extraction rate must therefore vary also. Let’s not also forget that the process is dynamic (so it varies with time also). It is thus inherently uneven.

Thinking about the mechanisms of diffusion (and washing) I wonder how much it actually matters which portion of water a given fraction of the extractable material is “extracted” into anyway.

However, my thoughts otherwise align with Alexander’s (@lakesidecoffee) comments - reducing the flowrate early in the shot increases the residence time, which would likely increase the concentration of the fluid in the puck. The effect of this would be an increase in the viscosity and therefore in the resistance to flow - meaning you get the same pressure drop, at a lower flowrate. If your objective is to prevent channelling, seems like a reasonable approach.

(Scott Burlington) #23

There will always be one end of the puck getting hit with water for longer than the other. The lower pressure at the beginning just minimizes that effect. Right?
It allows water to saturate the puck in a “low extraction” mode so that the flow of the higher pressure (higher extraction mode) takes place with the entire puck in its stream.
The only way I see to combat that uneven extraction would be to have some sort of 360 degree shower screen that hits the puck from as many angles as possible. Hopefully at first with low temp/low pressure water and ramp both up.

(Anthony) #24

What are people’s take on installing slower flowing gicleur on machines with fixed pre-infusion times? It seems like you would be giving up on the pre-infusion in exchange for the lower water debit. 1 example is on the Linea Mini with a 1second on and 1 second off preinfusion.

(Chris Bodnar) #25

I’ve read that a lot of people have had great success in swapping gicleur sizes on their machines (Linea’s in particular), especially if pump pressure is adjusted to 7 or 8 bar. There’s one particular forum that has a ton of write up on the LMLM in particular - a quick Google search will reveal of a wealth of info for that specific example!

(Anthony) #26

I assume youare referencing Home Barista. There is a thread dedicated to this for the mini but not one person raised a concern on how that might be affecting preinfusion unfortunately.

Weird flow on Aurelia II
(Emanuel Greucean) #27

@MattPerger This topic is very helpful to me and it motivated me to get Flow Restrictors for my brand new Rocket R9 that we got for our coffee shop.

I now have 0.5mm Gigleurs, and with the machine set at ~7bar I get a 200ml/30s water debit w/o the portafilter.
That is awesome, and before I got my refractometer I was extracting better espresso shots with a 20/40 recipe at 30s. Depending on coffee I would change the yield to adjust for taste. For example my Guatemalan origin would taste better with a 20/37 recipe.

I recently got my hands an Atago PAL-Coffee refractometer and started working on my recipe again to try to make it better, and get a better Extraction.
This is nice, but I discovered that I can do better, problem is that I can’t get my extraction above 17,9%.

This is my last recipe attempt:
IN: 20g; OUT: 40g (volumetric + scale)
Temp: 92,5 C; Time: 35s
TDS: 8,95%; TDS (g): 3,58 g
Ext Yield: 17,9%

How high is to high for the extraction time?
I’m thinking of changing my Pressure up a bit to get ~230ml/30s.

The coffee I used is a Panama Bouquet from Casa Ruiz, a medium omniroast.
The grinder is a Quamar Q13/75 E.