"A better way to grind coffee" from Washington Post - "Moisture-controlled triboelectrification during coffee grinding"

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romlee
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#1: Post by romlee »

Washington Post wrote:Grinding coffee is a messy business. Static electricity builds up on the grounds, leaving a clingy mess stuck in the grinder. Now, a team of chemists and volcanologists at the University of Oregon have unraveled precisely how moisture affects the buildup of static - and they've come up with a simple solution.

According to the researchers, adding a spritz of water to the beans before grinding cuts static. It also happens to create a more consistent, stronger-tasting shot of espresso.

(cont'd)
https://www.washingtonpost.com/science/ ... c-droplet/

This will come as no surprise to many here.
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baldheadracing
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#2: Post by baldheadracing »

tl;dr: RDT works.

Source paper: https://www.cell.com/matter/fulltext/S2 ... 23)00568-4
Moisture-controlled triboelectrification during coffee grinding
Joshua Méndez Harper, Connor S. McDonald, Elias J. Rheingold, Lena C. Wehn, Robin E. Bumbaugh, Elana J. Cope, Leif E. Lindberg, Justin Pham, Yong-Hyun Kim, Josef Dufek, Christopher H. Hendon

Highlights
• Identifying the coffee properties that govern triboelectric polarization of coffee
• Whole-bean moisture content below 2% causes negative particle charging
• External water passivates surface charging but does not create clumping
• With fixed espresso brew parameters, charge reduction increases coffee extraction

Progress and potential
Coffee grinding produces large quantities of static charge due to both fracturing and rubbing. Charge causes particle aggregation and discharge, a familiar problem in industrial coffee production. This study demonstrates that the magnitude of charge depends on the roast profile and, more importantly, the internal moisture content of whole-bean coffee. In an effort to control the charge, we demonstrate that the addition of external water mitigates its accumulation during grinding and promotes particle declumping. Notable differences in brew parameters are achieved. Implementation of our findings directly addresses a key issue of static accumulation and particle clumping and highlights the challenges of making physical property predictions based on bean color.

Summary
Granular materials accumulate surface charges through triboelectrification and fractoelectrification-charging resulting from material friction and fracture, respectively. These processes occur during coffee grinding and impact coffee production at both the enthusiast and industrial-length scales. By sourcing commercially roasted coffee as well as roasting our own, we find that roast color and grind coarseness impact the charging; fine, darker roasts acquire charge-to-mass ratios comparable to those inferred from particles in volcanic plumes and thunderclouds. Furthermore, we elucidate the influence of residual internal moisture on electrification, concluding that moisture can tune both the magnitude and polarity of charge. In addition to possible technological applications, we demonstrate that the addition of external water simultaneously suppresses surface charging and clumping of ground coffee and results in notably different flow dynamics in espresso formats, likely yielding markedly different taste profiles and more concentrated extracts.
-"Good quality brings happiness as you use it" - Nobuho Miya, Kamasada

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yakster
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#3: Post by yakster »

I became aware of a scientific paper regarding moisture and static during grinding: "Moisture-controlled triboelectrification during coffee grinding." I haven't had time to read this, but it should make for an interesting read.

https://www.cell.com/matter/fulltext/S2 ... 23)00568-4

They do mention the Ross Droplet Technique in the paper but appear to stop short of crediting David Ross specifically.

Previous closed thread for reference: Ross Droplet Technique-Eliminating Grinder Static
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randytsuch
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#4: Post by randytsuch »

Did a quick read, found this section interesting, where the pulled shots and compared with and without adding water before grinding.
I bolded the sentences highlighting the differences.

The impact of the water addition during grinding was demonstrated by brewing some espresso. There, all espresso parameters were kept constant (18.0 g dry mass coffee was used to produce 45.0 g liquid coffee extract, ground at setting 1.0, tamped at 196 N, and brewed using 94°C water, kept at 7 bar static water pressure with a 2-s pre-infusion), and shot time and flow rate were hence dependent on the particle size and permeability of the espresso bed. From the data presented in Figure 7, several physical differences are noted. First, the shot time is nearly 50% longer for coffee produced using the addition of water. We understand this to be due to increased bed density; because the fines and boulders are not electrostatically attracted to one another, the average particle size is smaller. Second, despite this, the first drops of coffee make their way to the cup at approximately the same time (10 s). At the end of the shot, the espresso prepared without water added to the whole beans produces a cup concentration of 8.2% total dissolved solids (TDSs), while the addition of water yields a cup with 8.9% TDSs. Perhaps the increase in concentration could simply be attributed to elongated contact time, but as we highlighted in an earlier paper,26 shots with the same degree of extraction but different time parameters should have markedly different flavors.

Randy

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HB
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#5: Post by HB »

Ref: Ross Droplet Technique-Eliminating Grinder Static
Now, a team of chemists and volcanologists at the University of Oregon have unraveled precisely how moisture affects the buildup of static - and they've come up with a simple solution.
Wow, it only took them 11 years. :lol:
Dan Kehn

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gonzomup
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#6: Post by gonzomup »

HB wrote:Wow, it only took them 11 years. :lol:
It probably took that long for the grant application and funding to get approved. :lol:

Mat-O-Matic
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#7: Post by Mat-O-Matic »

Making the rounds in news media today, a paper in the journal Matter upholds RDT and looks at several other espresso topics, including describing espresso brewing as being very similar to volcanic eruptions. :D

Summary at the Guardian.

Journal article.

A search of Matter shows several older espresso-related articles that, I assume, have already been posted.
LMWDP #716: Spring comes, and the grass grows by itself.

Mat-O-Matic
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#8: Post by Mat-O-Matic »

I like that espresso brewing is very similar to volcanic eruptions.
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jpender
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#9: Post by jpender »

Moka pots too. The final sputtering stage has been termed the "strombolian phase".

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yakster
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#10: Post by yakster »

The don't appear to mention the use of ion generators / ionizers like the Acaia Ion Beam in the paper. I'm a bit surprised.
-Chris

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