Posted Tue Nov 13, 2012, 2:23pm Subject: Grinder Assessment Using Sieves
So, I thought I'd take a quick look at grinder settings (LIDO) and a couple of sieves.
First characterization for a grinder would be "average" particle size. Second characterization would be distribution of grind. Finally, an assessment of fines (particles <150 microns) would be nice.
I figured that the first bit of info to know is what the different settings do for average particle size - and the easiest way to do that would be to find the setting of the grinder where 50% of the grounds would be retained on a particular sized sieve after several minutes of shaking.
Is it ever that easy?
Of course not. LOL
On average, I've kinda gotten (small sample sizes) settings of 1.5, 1.75 and 2.0 for the LIDO to get approximately 50% pass through a 710micron particle sieve. However, the amount passing through a 500 micron sieve varies - with less passing through for the 2.0 setting vs the 1.5 setting.
Something curious is going on. By taste, I really like the balance of steep time and draindown in a CCD with 1.75. 1.5 can get a twinge of bitterness if left a bit too long (about 3 minutes before drawdown). 2 and above end up with a handful of stubborn particles floating that take some time to submerge - and the draindown is quicker (an expected effect).
This implies that the changes in the settings for this burr set may not affect the overall average particle size so much as the distribution of particles. What is even more curious is when the average particle size drops - this doesn't leave a lot of room in the adjustment to go from average particle sizes of 700microns at 1.5 to very fine (200 or so microns) expected at setting=0 (or "Turkish).
Hopefully, when I get some more time next week, I'll grind through (pun intended) the settings on my grinder(s) to achieve 710 micron, 600, 500 and 425 micron 50% passthrough (by mass). Though, ideally I'd like to know the full particle count and distribution - I just don't see a laser differentiometer in my short term budget...
------------------------------------------ ----------------------------------------- Le café doit être noir comme le diable, chaud comme l'enfer, pur comme un ange, et doux comme l'amour.
"There is no right answer with coffee. There is only the elixir in your cup at the moment you partake."
"...I often say that when you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind;..." - Lord Kelvin RECIPES thread => http://www.coffeegeek.com/forums/coffee/machines/585708
Most likely this is the case. So I don't plow through kg of coffee, I was initially trying to do this on 5g samples - I figured with 500 discretion points it would work good enough. 2.3-2.5g retained on the screen for all three settings, but also lost a couple hundredths with static (using a small 2" plastic sieve, some gets trapped in the gasket) and repeatability was an issue, and they didn't exactly correlate to the grinder setting. Gonna have to re-do it anyways, and Revolution was coming on... :D
Surprising amount of clumping on 500micron.
I'll probably increase this to 25g samples.
Also, I looked at the designation (labeled as OPN) incorrectly. It wasn't a 710 micron - it was the 850 micron. They label the sieves in thousands of inch "OPN", but equivalent is ASTM-E11. I looked at the 30 OPN and assumed it was 710 micron, because 0.03/25.4~760ish, but what they label as "30 OPN" is ASTM-E11 #20 which is .0335" opening or 850 micron.
I don't understand why they can't just use METRIC!!!
Found that data last night. I think that 30 seconds isn't enough vibration. I think on MPE Chicago's site, they mention requiring a 5-minute vibration. Just shaking 5g samples until the resulting amount in the pan stabilized took several minutes.
Anyways I don't think my measurements are that far off from their findings.
I re-plotted their data as cumulative - what I was intending to do eventually (running grounds through the sieve series, developing the cumulative distribution, etc.)
Note that the Ditting has a steeper slope - on a cumulative distribution plot with a probability distribution, steeper slope means smaller sigma (less variation).
Running a whirlyblade for ~12 seconds can give you about 35% pass through a 500 micron sieve but 50% pass through an 850 micron sieve. That's the "boulders and dust" effect.
(Click for larger image)
------------------------------------------ ----------------------------------------- Le café doit être noir comme le diable, chaud comme l'enfer, pur comme un ange, et doux comme l'amour.
"There is no right answer with coffee. There is only the elixir in your cup at the moment you partake."
"...I often say that when you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind;..." - Lord Kelvin RECIPES thread => http://www.coffeegeek.com/forums/coffee/machines/585708
Posted Wed Nov 14, 2012, 6:51am Subject: Re: Grinder Assessment Using Sieves
Here's a look at OE's data (cumulative retained for each of the sieves) for the three settings I quickly investigated.
My data location is circled in red. X-axis is millimeter sieve opening, Y-axis is fraction retained on the screen.
(Click for larger image)
------------------------------------------ ----------------------------------------- Le café doit être noir comme le diable, chaud comme l'enfer, pur comme un ange, et doux comme l'amour.
"There is no right answer with coffee. There is only the elixir in your cup at the moment you partake."
"...I often say that when you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind;..." - Lord Kelvin RECIPES thread => http://www.coffeegeek.com/forums/coffee/machines/585708
Posted Wed Nov 14, 2012, 8:56am Subject: Re: Grinder Assessment Using Sieves
This should be fun. I have a Fisher 850-micron sieve, too--wrote about it here a while back (with pics).
Netphilosopher Said:
I think that 30 seconds isn't enough vibration. I think on MPE Chicago's site, they mention requiring a 5-minute vibration. Just shaking 5g samples until the resulting amount in the pan stabilized took several minutes.
Did you really achieve "stabilization," as you said? In my limited experience sieving I found that the more I shook the more coffee passed through the sieve (hence the need for a more consistent method of agitation), but then again I never went at it for more than a minute.
Posted Wed Nov 14, 2012, 10:17am Subject: Re: Grinder Assessment Using Sieves
jbviau Said:
This should be fun. I have a Fisher 850-micron sieve, too--wrote about it here a while back (with pics).
Did you really achieve "stabilization," as you said? In my limited experience sieving I found that the more I shook the more coffee passed through the sieve (hence the need for a more consistent method of agitation), but then again I never went at it for more than a minute.
Yeah, eventually no more particles will pass through the sieve. I assumed that as long as I wasn't using the sieve to "grind" that eventually all the particles would be segregated.
Some can get stuck in the mesh, tho. I've wondered if I took a fine brush and kind of back-picked the mesh every once in a while (to push-back any lodged particles).
------------------------------------------ ----------------------------------------- Le café doit être noir comme le diable, chaud comme l'enfer, pur comme un ange, et doux comme l'amour.
"There is no right answer with coffee. There is only the elixir in your cup at the moment you partake."
"...I often say that when you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind;..." - Lord Kelvin RECIPES thread => http://www.coffeegeek.com/forums/coffee/machines/585708
Posted Wed Nov 14, 2012, 12:15pm Subject: Re: Grinder Assessment Using Sieves
So, I took a closer look at OE's sieve data. Interesting.
If we make the assumption that the sieve levels are essentially cumulative distribution points, then we can fit that with a calculator for a normal distribution CDF, or use a Weibull (less intuitive - you get a k and lambda, but to many people these parameters are less intuitive than mean and sigma) distribution.
In the end, it looks like a normal distribution is plenty fine for using the experimentally gained Cumulative Probability function, which yields a mean and sigma. Keep in mind that because the particle bins for the data histogram are large, the histogram won't look correct. This is an artifact of the data - just because the 1mm to 1.4mm bin is so big doesn't necessarily mean that the average particle size lies within that block. The data is VERY useful, though, to treat as a cumulative distribution.
All we need to do is fit the CDF (obtain the Xbar and Sigma that matches the CDF). If the error is small enough (by judgement) this implies that a normal distribution is acceptable.
Here's the Ditting (undisclosed setting).
(Click for larger image)
------------------------------------------ ----------------------------------------- Le café doit être noir comme le diable, chaud comme l'enfer, pur comme un ange, et doux comme l'amour.
"There is no right answer with coffee. There is only the elixir in your cup at the moment you partake."
"...I often say that when you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind;..." - Lord Kelvin RECIPES thread => http://www.coffeegeek.com/forums/coffee/machines/585708
Posted Wed Nov 14, 2012, 12:17pm Subject: Re: Grinder Assessment Using Sieves
And here's the semi-equivalent mean setting (Lido set to 1.75) but shows slightly more variation:
(Click for larger image)
------------------------------------------ ----------------------------------------- Le café doit être noir comme le diable, chaud comme l'enfer, pur comme un ange, et doux comme l'amour.
"There is no right answer with coffee. There is only the elixir in your cup at the moment you partake."
"...I often say that when you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind;..." - Lord Kelvin RECIPES thread => http://www.coffeegeek.com/forums/coffee/machines/585708
Posted Wed Nov 14, 2012, 12:20pm Subject: Re: Grinder Assessment Using Sieves
And here is the CDF data fit for the LIDO set at 0.75.
Note the appearance of the histogram - doesn't "look" right, but it is fairly spot on if you consider it a cumulative distribution sorter.
(Click for larger image)
------------------------------------------ ----------------------------------------- Le café doit être noir comme le diable, chaud comme l'enfer, pur comme un ange, et doux comme l'amour.
"There is no right answer with coffee. There is only the elixir in your cup at the moment you partake."
"...I often say that when you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind;..." - Lord Kelvin RECIPES thread => http://www.coffeegeek.com/forums/coffee/machines/585708
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