WLL Grinder Retention Test

Grinders are one of the keys to exceptional espresso. Discuss them here.
Fluffeepuff
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#1: Post by Fluffeepuff »

Just saw this on YouTube.
I like his challenge at the end. Any takers? :mrgreen:

thecoffeefield
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#2: Post by thecoffeefield »

I saw that too and I thought it was interesting considering that I have less than 1gm retention. 4gm with the mini sounds off

mitch236
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#3: Post by mitch236 »

I wish they would have included the Monolith (either burrset) and the EG-1.

I had a Robur-E and can attest to the immense retention Mazzers have. The basic design that they all share isn't designed for single dosing.

CwD
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#4: Post by CwD replying to mitch236 »

Probably left em out because they don't sell either of those.

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iploya
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#5: Post by iploya »

I always enjoy WLL's videos. I love that they performed the experiment and shared the results. But I must say I am a little skeptical about the methodology - cleaning the grinder completely, grinding just one 18g dose, weighing the grounds dispensed, and subtracting the difference. That's just one dose starting from a full clean. In the real world, the retained grounds accumulate over time and many doses. Just see photos I posted in the E6P thread by way of example. So I suspect the dynamics are a little more complicated in terms of how each subsequent shot is tainted by multiple (not just one) prior dose. I would expect that, a glob of retained grinds in the chute "feed" into the new coffee being ground, and the extent and rate that the old, retained grinds infuse into the new grinds would be unpredictable, and that it might take the equivalent of several doses of new coffee being run through before all the old grounds are flushed out. But then, I operate my grinder in hopper mode and not single-dose mode. If you take the trouble to fully clean out between shots then the methodology in the video would be more applicable, but that approach is mostly impractical.

allwooba
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#6: Post by allwooba replying to iploya »

Agreed .. but wouldn't the conclusions still be valid? Maybe worse in the real world, but not better.

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iploya
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#7: Post by iploya »

What I am trying to say is, I am not sure what conclusions can be drawn from this test methodology, except maybe Mark's conclusion at the end of the video: "with the exception of the Mazzer, you don't need to grind out and throw away coffee to get a fresh [for practical purposes] dose."

The reason I say this is, he runs 3 tests for each grinder, and averages the result. For most of the grinders, the amount retained after one dose is a fraction of a gram. BUT, he completely cleans the grinder before each of these 3 tests. My observation is that the amount of retained grinds is cumulative, over several or many doses, assuming you do not take apart and clean your grinder between each dose. To make up an example, maybe on dose 1 you only accumulate .5g. Dose 2 might accumulate an additional .4g (.9 total retained). Dose 3, another .3g (1.2 total retained), and so on. After some number of doses, you will probably max out on some number - let's say, 5 total grams, once the chute, the gap between the burrs and chassis, and all other space has been filled.

THEN, the big question is, how much of the cumulative retained grounds ("stale") are released into each new ("fresh") dose? Because of the design and geometry, one would expect that not ALL the old grounds are pushed out first, before new grounds are dispensed into your portafilter. If you look at the geometry of my e6P, for example, the large, rectangular chute is covered by an anti-clumping screen that leaves only a small slit at the bottom. So, as new grounds are dispensed, the entire volume of that chute is NOT going to come out first. It will likely stay there and bleed out to some extent over time.

If you want a way to confirm this, run your home grinder until no more coffee comes out, then run some of those yellow Grindz cleaner pellets through it. Initially you will not see yellow grounds. You will see brown, stale coffee grounds come out first, followed gradually by a mix of brown/stale and an increasing amount of yellow grounds, until eventually you get mostly yellow grounds out. And when you refill your hopper with coffee after using Grindz, the reverse will happen -- you will have to run your new coffee through the grinder for some amount of time before you stop seeing yellow mixed in.

So, to me, a more useful test would be to do just that -- run a bunch of coffee through each grinder until max retention is likely to have occurred. Then with the hopper empty, grind until nothing more comes out. Next, run yellow Grindz through as a tracer, and monitor the total time it takes before you no longer see ANY brown coffee grounds included in the yellow Grindz grounds.

Another, even more meaningful test would be to run a bunch of coffee through each grinder until max retention is likely to have occurred. Then with the hopper empty, grind until nothing more comes out. Next, refill the hopper and immediately dispense an 18g (double) dose. Finally, analyze that sample to determine the percentage of yellow Grindz inside the total 18g dose. That percentage represents the total stale coffee in your "fresh" dose.

mrjag
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#8: Post by mrjag »

iploya wrote:... I suspect the dynamics are a little more complicated in terms of how each subsequent shot is tainted by multiple (not just one) prior dose. I would expect that, a glob of retained grinds in the chute "feed" into the new coffee being ground, and the extent and rate that the old, retained grinds infuse into the new grinds would be unpredictable, and that it might take the equivalent of several doses of new coffee being run through before all the old grounds are flushed out.
WLL's argument is based on the assertion that you can't taste a difference between true zero retention (18g in, 18g out) and nearly zero retention (18g in, 17.25g fresh/0.75g stale out). If you take that as a given, then it doesn't matter how long the retained grinds stay in the system.

DaveC
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#9: Post by DaveC replying to mrjag »

The big problem is his tests are meaningless. He clearly said he cleaned the grinders, then put in ,a measured dose, weighed what came out and then repeated the process including the entire deep clean. This does not properly test

retention
exchange (old for new coffee)
dose consistency

A grinder will continue to retain coffee for more than just 1 double shot. use a grinder for 10 or 20 shots and the retention in the grinder is larger than after 1 shot. It reaches a maximum point, but that point is not reached after a single grind through. Worse still he gives you the average of the 3 cycles, not what each cycle was, so even for an invalid test, you can't see the variance.

To properly make statements about retention, exchange and dose consistency, the grinder has to have real world testing parameters and the potential for exchange fully explored. This can only be possible by properly measuring retention by weighing what's left in the grinder (after at least 3 shots, preferably much more, like a days use)...not sweeping it all away with big brushes and vacuum cleaners. doing this gives you the potential for exchange and then dose consistency average, gives you the likely minimum value for exchange.

A nice video with an easy message, it looks very impressive but unfortunately not a correct message.

it tells you what might come out of a totally cleaned grinder on the first 20g shot (although they may not have been completely cleaned, difficult to tell), but even then, you only get an average, rather than the 3 figures, so you can't even make a stab at whether it's + or - n gram

InspectorGadget
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#10: Post by InspectorGadget »

It seems comments on the Mazzer Robur must apply to the E model if you are talking retention even though I saw a good article on this forum demonstrating very little retention on the Robur doser model.

I use the Doser Rober and honestly retention is small to non-existent. I struggle to see how it can retain unless people are in some sort of high humidity environment where something sticks and simply won't shift.

I would say that the Robur retains less than any other grinder I have owned including the Macap M4D and others.

I don't think I'm being retentive here anally or otherwise and yes some grinders maybe do retain more than others because of anti-static screens and other design factors.

It appears here maybe it is some design feature of the Robur E if retention is a problem with the E model. Retention is definitely not an issue with the Robur doser model though.

I enjoy the doser too.

I just watched the video and not a single Doser grinder tested. This is interesting as if you look in a cafe there are still plenty of Doser grinders and not only that they are often a much cheaper option than the doserless. The doserless options require more tricks to try to minimise clumping maybe whereas a doser grinder thwacks clumps pretty well. I get zero clumps on the Robur doser.

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