Coffee Data Science
Does WDT Migrate Fines to the Bottom of the Espresso Basket?
The Weiss Distribution Technique (WDT) has been around for a few years now. WDT generally helps with good distribution and has been found to improve coffee extraction. One difficulty people have had is knowing how long to WDT. If you WDT too much, do finer particles migrate towards the bottom of the filter basket from the general mixing and movement?
I theorize that the finer particles stick to larger particles due to static. My previous experience with sifting showed that simple vibration was not enough to cause particles to separate enough. I had to intensely sift indicating that ground coffee didn’t act like dry sand.
To test this, I looked at the grind distribution on a few samples after some WDT, more WDT, and too much. For each iteration, I would tamp the puck afterwards and pull a core sample. I used freshly ground coffee as well.
Then I would continue to WDT the coffee.
I ended up with these three core samples. These samples were pulled from the center of the puck.
Using image processing, I measured the distributions for starting distribution, first WDT application, second and third. For each of these, I measured the distribution at the top, middle, and bottom of the puck.
I did not see a shift in the distributions that indicated a distribution change.
I looked more closely at the fine layer, and while there is some movement, it doesn’t match the expectation of a migration. For example, I would have through the top could have had a decrease in particles less than 200um, but it had an increase over time.
I look at the coarser particles as well, and I looked at them in reverse so I could understand any changes going on. There wasn’t any apparent trend.
From this set of experiments, I did not find evidence that WDT causes finer particles to migrate during shot preparation. It is quite possible due to my technique, but I don’t have data to support a different conclusion.
So if you’re worried you’re doing too much WDT, take a breath.
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