WDT - Effect of Grinds Stirring

Beginner and pro baristas share tips and tricks.
User avatar
luca
Team HB

#1: Post by luca »

In my naive quest to try to buy coffee from local roasters to support them during the pandemic, I have ended up with lots of coffee that is undrinkable, so I've decided that I'm going to use some of it for experiments.

Yesterday, I burnt through a 250g bag to try to pull multiple shots to investigate what stirring as part of the WDT does. I dialled it in for 15.0g dose shots using WDT, on a profile that was preinfusion until the puck is saturated, then flat 8.6bar pressure. I pulled 12 shots and discarded 6 for not being dialled in, or because I screwed up and hit tare on the scale at the wrong time so I couldn't measure the dose properly.

I used this distribution tool (Levercraft Ultra) and either shoved the prongs right to the bottom of the basket and stirred 30 times, to stir it very thoroughly, or I shoved the prongs about half way down the basket and stirred once, just to distribute the central mound to the edge. Here is the tool:




Here is what the puck looked like after 30 stirs, before tamping:





I tamped with the The Force tamper, flat base, twice. You can debate whether it's a good or a bad tamper, but for present purposes, it's consistent. I also used the Monolith Max grinder with SSP burrs, which are now called "Low Uniformity", I gather. Again, you can debate whether those burrs are good or bad, but, again, it's not the point. I took TDS measurements:




I ended up with 2 sets of 3 shots to compare. Shot 9 was pretty questionable; I can't remember, but I may have screwed up on weighing that, so perhaps that should be discarded. "Total" in the table below is total time, and you can see for shot 9 it was pretty high. Here are the raw results:




None of this tells you what you should do to make espresso, since higher or lower EY might be better or worse for a particular coffee. What this does do is to provide some evidence that WDT techniques do, in fact, make a pretty significant difference. From the above you can see that fiddling a lot, compared with minimally fiddling, results in a drop of extraction yield in the order of 1.5%. Call it 1-2% to allow a margin of error.

A large limitation with the above is that no one WDT stirs 30 times, right to the bottom, with such a device, though it's fast enough that you could if you felt it was beneficial. The reason why I chose to stir 30 times was to try to exaggerate the impact of stirring. Further experiments should be conducted with more sensible things that people are actually likely to do. For now, this is just a result that gives us some vague insight.

We can discuss that, of course, there are a tonne of limitations to this. The sample size is small. I haven't done stats to get a proper margin of error (and the number of results might not even be statistically significant). Perhaps different grinders that clump more will have different results. Maybe changing equipment or coffee will change things. I also screwed up several times in doing this, not taking proper measurements, hitting tare at the wrong time and - the thing that irritated me the most - I set my synching program to push from my laptop to my tablet, so I inadvertently deleted all of the shot history files that I had hoped to extract to graph. I was really disappointed with myself for doing that, because one of the things that I was really hoping to be able to see from putting the six graphs on the one axis was whether one set of shots sped up more than the other throughout the extraction, which is information that we're unlikely to reliable get unless someone graphs it with a DE or an Acaia. Finally, another limitation of course is that I didn't taste anything, since the coffee was gross.

But what I did want to do on this was to move us towards actually sharing and discussing real data. I'm very sick of people making generalisations that are not based on on either actual taste results in the cup or actual data. Discussing actual data is of course difficult, since gathering the data is a thankless chore. Doing the above took me about an hour just to pull the shots, and it's not a particularly impressive data set. But the corollary of my data not being good is not that the opposite is true. It's that we need better data. I'm posting this here in the hope that it might inspire people to give collecting and sharing some data a shot, even if the data isn't great.
LMWDP #034 | 2011: Q Grader Exam, Brewer's Cup #3, Australian Cup Tasting #1
★★★ Very Helpful

Flair Espresso: handcrafted espresso. cafe-quality shots, anytime, anywhere
Sponsored by Flair Espresso
User avatar
keno

#2: Post by keno »

Nice experiment, kudos! Thanks for taking the time to do this and for reporting the results.

I agree with you about the importance of having solid data and also about taste being the ultimate arbiter. I'd be curious what you think about the taste difference between the two methods, but the main shortcoming is that you used throwaway coffee and so didn't taste it.

My initial reaction was that people may find the data counterintuitive - eg, that WDT should help to increase extraction. But actually I think that the data may make a lot of sense in that without WDT there is more fines migration which slows down the flow (witnessed in the longer shot times for the no WDT arm) hence the higher extraction yield. With WDT the shot may flow a bit quicker and more consistently, which helps with dialing in and repeatability. In my personal experience WDT helps to improve clarity and bring out brighter flavors, so shots with WDT taste less muddy and over-extracted.

Would be nice to repeat the experiment with some good coffee, increase sample size, incorporate blinded taste testing, and get your data on shot flow rate over time.

Jeff
Team HB

#3: Post by Jeff »

Great work Luca!

I'm wishing I had a refractometer when I eliminated paperclips and hooked/looped ends from my list of stirrer contenders.

Did you happen to notice if, when you "shoved the prongs right to the bottom of the basket" if the face of the basket visually showed more of an uneven pattern of extraction than with only going part way down? I noticed distinct unevenness with my early use of the LeverCraft tool. From Review - LeverCraft Ultra WDT Distribution Tool. I have hypothesized, but not been able to support one way or another than it has to do with the spread of the tines.

Quickly stirred to full depth:



More carefully and thoroughly stirred to full depth, then working up to the top.


User avatar
luca (original poster)
Team HB

#4: Post by luca (original poster) »

My initial reaction was that people may find the data counterintuitive - eg, that WDT should help to increase extraction. But actually I think that the data may make a lot of sense in that without WDT there is more fines migration which slows down the flow (witnessed in the longer shot times for the no WDT arm) hence the higher extraction yield. With WDT the shot may flow a bit quicker and more consistently, which helps with dialing in and repeatability. In my personal experience WDT helps to improve clarity and bring out brighter flavors, so shots with WDT taste less muddy and over-extracted.
Yeah, one of the things that I did really want to get an inkling of is if one would speed up faster than the other, so I was super annoyed with myself to have the shot data overwritten.

I should be super clear that these shots were at the same grind setting. Maybe with 30 stirs, you can grind finer to get the same extraction time and bump up the EY? And then, followup question, of course: ... would that taste better or worse?
Would be nice to repeat the experiment with some good coffee, increase sample size, incorporate blinded taste testing, and get your data on shot flow rate over time.
Yep, would be great. Who's paying for it?
LMWDP #034 | 2011: Q Grader Exam, Brewer's Cup #3, Australian Cup Tasting #1

User avatar
luca (original poster)
Team HB

#5: Post by luca (original poster) »

Did you happen to notice if, when you "shoved the prongs right to the bottom of the basket" if the face of the basket visually showed more of an uneven pattern of extraction than with only going part way down? I noticed distinct unevenness with my early use of the LeverCraft tool. From Review - LeverCraft Ultra WDT Distribution Tool. I have hypothesized, but not been able to support one way or another than it has to do with the spread of the tines.
I specifically avoided looking at that, because that's too complex. I wanted a simple question, capable of answer, which was just generating the results in that table.

To be very blunt, I don't know how useful any of that information about what beads where actually is, and I'd prefer to pay attention to the results in the cup than something like that, which is difficult to quantify. Is there some study around somewhere, where people have actually correlated any of that with results in the cup? Like I know everyone just loves to assume that "evenness" = better, but that really needs to be put to the test. It might not make a jot of difference.
LMWDP #034 | 2011: Q Grader Exam, Brewer's Cup #3, Australian Cup Tasting #1
★ Helpful

User avatar
RapidCoffee
Team HB

#6: Post by RapidCoffee »

Luca, thanks for doing this (long overdue) study. I've been meaning to post results on this topic for some time, but it got lost in the shuffle.

So here's a quick & dirty reality check on my system:
DE1+ v1.0 espresso machine, Pavlis water
Baratza Sette 270 grinder, dialed in for ~30s pour time
Black Oak Heartwood blend, 17g dose
EP HQ 14g ridgeless baskets
Decent Tamper v1
fast preinfusion, then 9 bar flat profile at 90C
target weight 34g (brew ratio 1:2)
Atago PAL-COFFEE Refractometer


Procedure:
Grind coffee into two baskets
basket 1: level with finger and gentle shake, tamp
basket 2: brief stir with 4-prong keycap puller WDT tool, brief leveling nutation with tamper, tamp

no WDT on left, WDT on right

Run 1:
No WDT: 26s extraction, Brix 11.13% (21.4C), EY 18.9%
WDT: 31s extraction, Brix 10.55% (22.1C), EY 17.9%

no WDT on left, WDT on right

Run 2:
WDT: 30s extraction, Brix 10.13% (22.1C), EY 17.2%
No WDT: 27s extraction, Brix 10.78% (22.3C), EY 18.3%

no WDT on left, WDT on right

Observations:
* Baskets prepped with WDT take longer to extract to a given brew ratio. I've seen this consistently, ever since I developed this technique. This is probably due to reduced channeling. I do not understand why Luca got shorter pours with WDT preps.

* Baskets prepped with WDT feature significantly increased puck resistance (yellow lines in extraction graphs), for the same reason.

* Baskets prepped with WDT yield visually prettier pours, for the same reason. No WDT on left shows increased spatter.

no WDT on left, WDT on right

* Baskets prepped with WDT give lower refractometer readings (by ~1%EY). This corroborates Luca's results. My WAG: increased channeling on non-WDT baskets causes some overextraction, leading to higher Brix/TDS/EY.

* There were minor taste differences, which (like Luca) I did not pursue. In general, I preferred the WDT-prepped extractions. They tasted less harsh and had more clarity. But this was not blind taste testing, and yes I am biased. ;-)

I originally developed WDT for a ghetto-rigged doserless Mazzer Super Jolly grinder back in 2006. That grinder was a clump monster! So my focus back then was breaking up clumps. With my dosered Robur (and Sette), I use WDT primarily for randomizing grinds distribution. Neither of these grinders needs WDT, but I believe both still benefit from it.
John
★★ Quite Helpful

User avatar
Jake_G
Team HB

#7: Post by Jake_G »

I find it interesting that while both tests showed a lower EY, the big flat shots flowed faster with WDT than without (mine do, too) and the little conical shots flowed slower with WDT than without. Granted there was a nutating tamp added in with the WDT that could have slowed those shots down...

But I wonder if the burrs themselves rather predispose whether stirring will slow down the shot or speed it up? Could particle distribution play a role here?
RapidCoffee wrote:* Baskets prepped with WDT give lower refractometer readings (by ~1%EY). This corroborates Luca's results. My WAG: increased channeling on non-WDT baskets causes some overextraction, leading to higher Brix/TDS/EY.
Them's fightin' words, there, John

The narrative is that channeling can only reduce EY% assuming a zero-sum game of water's ability to extract. That is, if water is over-extracting coffee from region A, it cannot also be extracting regions B, C and D as effectively as if region A did not have channels in it. The idea being that water is lazy and will fail to properly extract the rest of the puck if you have channels anywhere in the puck.

So, you're challenging the narrative.

I like it.

But is there something else that could be going on?

Could it be that the sette extracts more with a faster flow rate, whereas the 98mm LU burrs extract more with increased contact time?

I left my optical refractometer in Oregon, so I can't play along right now, but I do wonder if the grind size had been adjusted to maintain shot times between WDT and non-WDT shots, what the results would have been...

With Luca's results or John's results in a vacuum,we could have easily argued that EY decreased because the shots flowed faster, or EY decreased because the shots flowed slower. Since we can't very well say that EY was decreased because the shots flowed both faster and slower, what then would the reason be for decreased EY in both cases?

I'm curious...
LMWDP #704

Baratza: skilled in the art of grinding
Sponsored by Baratza
User avatar
RapidCoffee
Team HB

#8: Post by RapidCoffee »

Jake_G wrote:Them's fightin' words, there, John
"You'll have to pry this refractometer from my cold, dead fingers..." :lol:

Not hardly. For starters, I appreciate that Luca put the time and effort into this little experiment. There's a tremendous amount of speculation on the coffee fora, and precious little actual data. In fact, I appreciated his work enough to put my time and effort into further experimentation. Which IMHO is the appropriate response.

I've run similar tests in the past, and these EY results corroborated both my earlier work and Luca's. The flow rate discrepancy is surprising, and I do not understand it.
Jake_G wrote:I find it interesting that while both tests showed a lower EY, the big flat shots flowed faster with WDT than without (mine do, too) and the little conical shots flowed slower with WDT than without. Granted there was a nutating tamp added in with the WDT that could have slowed those shots down...
I've gotten similar results from my Robur (hardly a "little" conical). Unfortunately I do not have a big flat for comparison. Perhaps you could try this? No refractometer required; just time your extractions.

My "nutating tamp" is not a tamp. It's a brief nutation, using only the weight of the tamper, in order to level the puck. It's part of my regular puck prep routine, and so I decided to include it.
Jake_G wrote:The narrative is that channeling can only reduce EY% assuming a zero-sum game of water's ability to extract. That is, if water is over-extracting coffee from region A, it cannot also be extracting regions B, C and D as effectively as if region A did not have channels in it. The idea being that water is lazy and will fail to properly extract the rest of the puck if you have channels anywhere in the puck.
As I said, it's a WAG. There's clear evidence in the posted extraction graphs of greater puck resistance in the WDT-prepped pucks. The obvious explanation is reduced channeling. You are welcome to posit other hypotheses. (I'm sure someone will suggest fines migration. :wink:)
John

Jonk

#9: Post by Jonk »

RapidCoffee wrote:* Baskets prepped with WDT give lower refractometer readings (by ~1%EY). This corroborates Luca's results. My WAG: increased channeling on non-WDT baskets causes some overextraction, leading to higher Brix/TDS/EY.
Perhaps unrelated, but I've seen the same effect when measuring pre-infusion vs. no pre-infusion. ~1%EY lower with pre-infusion in spite of seemingly more even extraction. Also not blind-tested but taste has been less harsh with pre-infusion. I've had the same WAG for a while. Repeated tests but small sample size.

pcrussell50

#10: Post by pcrussell50 »

Apologies if this has been covered as I have not read every post in detail. But over time I have come to see the need to differentiate the notion of "distributing" from that of "mixing", where they are not necessarily the same thing.

On purpose built single dosing grinders like my Monoliths and HG1 there is little mixing done by the grinder because there is no mixing or homogenizing device in the flow path. I find that I get best pours from those grinders if I grind into a separate vessel and mix aggressively, before transferring to the portafilter. Think something like the LWW blind tumbler/shakers. Then once in the portafilter, there is still the need to distribute before tamping or using spinny grooming tool or both. I see mixing as a much more aggressive thing than merely distributing a pile in the portafilter before tamp or spin tool.

Having made note of the difference between mixing, and pre-tamp distributing, it is likely possible to do both with one tool in one step especially if your grinder does some degree of mixing like grinders with long paths and static screens (Mazzer type), or rubber flappers (Baratza), or engineered compression chutes ((Sette style), and if you either have a funnel/cut yogurt cup or are not worried about spillage.

Anyway with my Monoliths (Flat and Max), and HG1, I found aggressive mixing to be mandatory, and there was still distribution to be done before tamp or tool.

-Peter
LMWDP #553