Deep Dive on Water Grinding Espresso (the Hendon papers)

An in depth look (and replication) of the big result from the recent papers published on adding water during coffee or espresso grinding to reduce static (sometimes referred to as RDT, Ross Droplet Technique). Does it work? Eh... not for me.
First paper: www.cell.com/matter/fulltext/...
Second paper: arxiv.org/pdf/2312.03103.pdf
=== Timestamps ===
00:00 Introduction
01:41 Fair Warning...
03:50 Why is this important?
04:20 My main concern
09:30 Material impacts on static
12:15 Roast level and static
18:08 Wherein I rant about "RDT"
21:43 Charge suppression by water
26:40 The big main result... Time/Extraction
32:14 Alternative hypotheses for the effect
36:36 The second paper...
38:23 Charge passivation strategies
40:17 Water isn't just about static...
45:03 A chart I'd like to see
47:47 Implications for normal people
49:56 Test: Replicating the paper
52:39 Test: Data and results
55:35 Conclusion

[@mulullama]

Now this is the level of coffee deep dive i can get behind🎉

[@robertebob]

nice video. thank you. i made it through the whole thing. grinders and burrs are everything and I'm going to guess RPM is also a factor with all the business of static. So many variables that would affect results. Meanwhile, I enjoy my home roasted beans and espresso, and I do add a couple of mist squirts to my 18g dose for grinding in my 1ZPresso K-Plus manual. I just strive for a repeatable work flow and hope for the best.

[@justinbouchard]

did they do pre infusion in the paper?

[@TechDregs]

Yes, two seconds.

[@justinbouchard]

and you ran at static 7 bars of pressure?
i also think they don't discuss the basket used at all as far as I can tell, they also don't discuss the flow rate the machine they used can provide at 7 bar of pressure. These are substantial factors that can't be reproduced without knowing these variables.

[@TechDregs]

I adjusted my machine to max at 7bar, but it really only peaked there and flowed more like 5-6 through a lot of the extraction. Flow rates are mostly dictated by shot time and result mass and are going to be pretty comparable no matter what machine you use... they have to be if you're pulling the same amount of expresso in the same amount of time. Slight nonlinearities can happen, but during the bulk of the shot time, flow is actually pretty linear.
IMO, none of the little details should matter that much. The basically treatment is what should drive the result, and if relatively normal puck prep and extraction methods can't reproduce their result, that tells me that it's probably just not a general result, and may actually be unique or specific to their exact setup. And that gets back to "maybe static isn't really that big of a deal".

[@justinbouchard]

i think that flow rate at 7 bar of the machine used and porosity of the basket are massive variables for reproduction.
to make a moderately facetious argument, if a pressurized basket was used to try and replicate this test, particle size is now irrelevant. as well as, if my machine could do 5g/s flow rate at 7 bar, the particles again do not matter.
for the every day hyper coffee nerd, taste is what matters, and if reduction of static during grinding makes more a more consistently even grind this must affect taste.
so for me, i don't think trying to replicate the tds and flow rate results are necessary, nor are they reproducible without the machine being used having the same capable flow rate under pressure, and the basket having the same porosity as that tested in the paper.
i actually think the addition of the possible affects during espresso brewing was a mistake to add in the paper, and definitely needs it's own research done just on that piece alone.
i think people are getting too excited for new coffee science in espresso so this got jumped all over immediately. the paper was about static during grinding. I think the major flaw of this paper in the sense of it as a whole is attaching "less staticy coffee makes higher extracted espresso".
it's clear that the coffee has basically zero charge positive or negative a short time after grinding. so to me, the static has absolutely nothing to do with espresso extraction. it has everything to do with grinding and how it affects particle size during this process.
so for me, everyone getting caught up on "rdt before grinding gives you higher espresso extracting" is a failure of the paper, and of the understanding of the paper.
if you're not having the same density of bean, ground at the same particle size, extracted under the same flow rate at the same pressure through a basket of the same porosity, this cannot be replicated at all.

[@TechDregs]

I think we're mostly in agreement. I think their conclusions re: shot time and extraction are much weaker than the rest of their paper. Their results on those attributes do not seem general at all, and a lot of people are probably going to be wasting their time worrying about static for no good reason.