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.
