Opinion on grind fineness to flow rate needed. I am trying to do a simple spreadsheet with the variables in pulling a espresso shot.
Dose in grams
Filterbasket hole size/number
Pressure
Time
Weight out
Volume out
Grind fineness
Then I can vary one parameter and see the effect on the others....at least in the speed sheet

My question is - is there a way to measure grind fineness? If not, then do we think that a grind that is 10% more fine flows water 10% slower? Is it a linear relationship?

If we knew the area of the flow path then Bernoulli Equation would be easy to apply. We can assume the same tamp pressure. I know there are many other variables like bean type, oil content, freshness, environment, consistency of grind, etc. The goal is not to get a exact answer but to make a sheet that would show trends and come close to quantifying the changes that happen when one variable is changed in the brew process. That way a person could play on the sheet and get an idea what happens to his shot time if he increases his dose 2 grams.....or what what volume out he can expect if he lowered the grind 10% but pulled the shot the same time.....you get the idea.

Thanks
Jeff

There is a way to measure fineness of grind, but I'm not sure... Well, anyway it's the Kruve Coffee Sifting System.

With a 50 micron difference between sieves at best, I don't think 10% is even close to being in the ballpark?

If accuracy was the highest priority, it would require a scanning electron microscope. I think even with a Ro-Tap sieve, if you're looking at espresso grind fineness, the lack of precision and accuracy will be far too great. Even laser particle analysis has problems, due mainly to the variability in the 3D shape of the particles if I'm not mistaken.

John Weiss is very strong on this topic, maybe he'll chime in.

IMHO, laser particle sizing is still the gold standard, despite issues with grind particle shape.

My suggestion:
1. Abandon your spreadsheet. It is unlikely you will find a linear relationship between grind setting, particle size distribution, dose, and flow rate. A certain amount of trial and error is part of the espresso process. Get used to it.
2. Pick a reasonable dose for your basket (e.g., 18g for an E61 double basket).
3. Adjust grind to achieve the desired desired brew ratio in 25-30s.
4. Vary other parameters (coffee dose, brew temp, extraction time, etc.) until you find a sweet spot for taste. This may involve further grind adjustments.
5. Repeat for each new bag of espresso beans.

For example, if you want a brew ratio of 50%, adjust the grind (by observation/trial and error) until you extract 36g in 25-30s. Ideally, blonding should occur at roughly the same time as your shot terminates.

Hi John,

What you described is exactly what I now do. It works well.

If one wants to quantify something additionally, a refractometer could be employed.